INTERNSHIP REPORT POWER GENERATION, TRANSMISSION, DISTRIBUTION AND PROTECTION SYSTEM EQUIPMENT OF DUTCH BANGLA POWER & ASSOCIATES LTD.

Transcription

1 INTERNSHIP REPORT ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND PROTECTION SYSTEM EQUIPMENT OF DUTCH BANGLA POWER & ASSOCIATES LTD. (DBPAL) By DEENA FARZANA ( ) AMENA BEGUM ( ) Submitted to the Department of Electrical and Electronic Engineering Faculty of Sciences and Engineering East West University In partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical and Electronic Engineering (B.Sc. in EEE) SPRING, 2012 Department of Electrical and Electronic Engineering, East West University 1

2 APPROVAL LETTER Department of Electrical and Electronic Engineering, East West University 2

3 ACKNOWLEDGMENT At the very outset, we wish to convey our heartfelt gratitude to Almighty Allah for His help to complete the Internship successfully. We also thank the management of Dutch Bangla Power & Associates Ltd (DBPAL) for providing us such opportunity to accomplish our industrial training. We would specially thank Engr. MD. Anharul Islam, Managing Director of DBPAL who gave us the permission to do internship work. We want to thank all those people who helped to complete our internship report successfully. In this process our special thanks goes to Superintendent Engr. Humayun Kabir (O&M), Engr. Kamal Hossain & Executive Engr. Shyamal Kumar Das who coordinated our internship program and helped us to get acquainted with other engineers. They helped us to learn the scheduled topic which was present in our internship training schedule. We also want to thank each and every employee of DBPAL for their continual support. We would also like to mention the name of Dr. Khairul Alam, Chairperson & Associate Professor of the Department of Electrical & Electronic Engineering, and East West University (EWU) for his support and encouragement throughout the period of our internship. We take this opportunity to extend our sincere thanks and gratitude to our honorable supervisors Tahseen Kamal, Senior Lecturer, Department of Electrical & Electronic Engineering, East West University (EWU) & Fakir Mashuque Alamgir, Lecturer, Department of Electrical & Electronic Engineering, East West University (EWU) for giving their valuable time for us to complete this report successfully. Last but not least we would like to thank the almighty Allah for giving us the chance to complete our internship and preparing the internship report. Department of Electrical and Electronic Engineering, East West University 3

4 EXECUTIVE SUMMARY We did our internship at Dutch Bangla Power & Associates Ltd (DBPAL) located at Ailpara, Siddhirganj, Naraynganj on the left bank of the river Shitalakkha from 26 th December to 12 th of January and this internship report is the result of those 15 days attachment with the DBPAL. During our internship period we gathered practical experiences over the topics related power generation, switchgear protection and power distribution which we have learned inside the class room or from books. In this report we have focused on the processes which are used in DBPAL. For power generation, HFO (Heavy fuel oil which is basically furnace oil) is used in DBPAL. Protection and controlling of the equipments of the power station is a very important and complicated task. With the help of the plant engineers we observed the control room and protective equipments such as: relays (VAMP 210 & VAMP 265 used in DBPAL), circuit breakers etc very closely and understood the functions and controlling system of those equipments. We acquired knowledge about various types of transformers, isolator, circuit breakers (SF6 and Oil), lightning arresters, current transformers, potential transformers and other equipments of the power station which were clearly taught and shown by the senior engineers of the power station of DBPAL. There are various types of tests (meggar test, motor test, transformer test) which are performed by the technicians and engineers of the DBPAL. Department of Electrical and Electronic Engineering, East West University 4

5 TRAINING SCHEDULE The following table shows our internship training schedule. Our weekly holiday was in Thursday. But in the last week we worked on Thursday instead of Friday. Day Starting time -- Ending time Topic Superintendent Engineer Total Hour Engr. Shaymal Kumar Monday AM to 5 PM Overview about Company/Safety Issues/Small Introduction about the Whole Power Plant Das Executive Engineer & Humayun Kabir 8 hours Superintendent Engr. Tuesday AM to 5 PM Oil comes from Burge to Engine/Auxiliary Unit/Current and Voltage levels/types of Grounding/DC system/frequency Engr. Shaymal Kumar Das Executive Engineer 8 hours Converter/MV & LV Switchgear Engr. Shaymal Kumar Wednesday AM to 5 PM Details of MV,LV & HV Switchgear Das Executive Engineer 8 hours Engr. Shaymal Kumar Friday AM to 5 PM HV Switchgear/Reading electrical drawing & Trouble shooting Das Executive Engineer 8 hours Department of Electrical and Electronic Engineering, East West University 5

6 Engr. Shaymal Kumar Saturday AM to 5 PM Operation Modes of Alternator & Engine Das Executive Engineer 8 hours Engr. Shaymal Kumar Sunday AM to 5 PM Synchronous Generator Theory/Maintenance of Alternator Das Executive Engineer 8 hours Engr. Shaymal Kumar Monday AM to 5 PM Details of Generator & Synchronization Das Executive Engineer 8 hours Engr. Shaymal Kumar Tuesday AM to 5 PM Protectional Relays & Generator Protection Das Executive Engineer 8 hours Engr. Shaymal Kumar Wednesday AM to 5 PM Generator Protection Das Executive Engineer 8 hours Engr. Shaymal Kumar Friday AM to 5 PM Transformer Das Executive Engineer 8 hours Engr. Shaymal Kumar Sunday AM to 5 PM Mechanical Power to Electrical Power Das Executive Engineer 8 hours Department of Electrical and Electronic Engineering, East West University 6

7 Engr. Shaymal Kumar Monday AM to 5 PM Mechanical Power to Electrical Power Das Executive Engineer 8 hours Engr. Shaymal Kumar Tuesday AM to 5 PM WARTSILA Engine Control System & Communication Layout Das Executive Engineer 8 hours Engr. Shaymal Kumar Wednesday AM to 5 PM Engine Operation Das Executive Engineer 8 hours Thursday AM to 5 PM WARTSILA Engine Safety Module/Main Control Module/Overview about the Whole Power Generation Engr. Shaymal Kumar Das Executive Engineer 8 hours Our Lunch break was from PM to PM. Department of Electrical and Electronic Engineering, East West University 7

8 TABLE OF CONTENTS APPROVAL LETTER... 2 ACKNOWLEDGMENT... 3 EXECUTIVE SUMMARY... 4 TRAINING SCHEDULE... 5 TABLE OF CONTENTS... 8 LIST OF TABLES INTRODUCTION COMPANY PROFILE OBJECTIVE OF THE INTERNSHIP SCOPE AND METHODOLOGY Scope Methodology SWITCHGEAR INTRODUCTION SWITCHGEAR Classification HIGH VOLTAGE (HV) SWITCHGEAR Lightning Arrester Capacitive Voltage Transformer (CVT) Insulator Isolator Busbar Current Transformer (CT) Circuit Breaker a Air Blast Circuit Breaker (ABCB) b SF6 Circuit Breaker c Oil Circuit Breaker (OCB) d Vacuum Circuit Breaker (VCB) e Air Circuit Breaker (ACB) f Miniature Circuit Breaker (MCB) g Molded Case Circuit Breaker (MCCB) MEDIUM VOLTAGE (MV) SWITCHGEAR Incoming from generator Outgoing feeder to generator transformer Station transformer (1600KVA) a Thermostat b Programmable Logic Controller (PLC) Metering or measuring panel Department of Electrical and Electronic Engineering, East West University 8 Page

9 2.5 LOW VOLTAGE (LV) SWITCHGEAR Frequency converter SINGLE LINE DIAGRAM DC SYSTEM VOLTAGE AND CURRENT LEVELS Rated current levels a Rated normal current b Rated short time withstand current c Rated peak withstand current d Rated short circuit breaking current e Rated short circuit making current Voltage levels a Nominal voltage level b High voltage level TRANSFORMER INTRODUCTION CONSTRUCTION OF TRANSFORMER TYPES OF TRANSFORMERS Dry Type Transformers Liquid Immersed Transformers OPERATION CRITERIONS OVERLOADS OF TRANSFORMERS FAULTS THAT CAN OCCUR Faults between MV winding turns Faults between LV windings Faults between MV and LV windings Faults between MV windings and earth Other examples of faults and results TESTING OF TRANSFORMERS Type Test Special Test Routine Test a Measurement of winding resistance Test b Measurement of insulation resistance Test c Separate source voltage withstand test (High Voltage tests on HV & LV) d Induced Over voltage Withstand test (DVDF test) e Measurement of No Load Loss & Current Test MAINTENANCE AND PROTECTION OF TRANSFORMER Maintenance a Oil b Bushing Protection ENGINE INTRODUCTION MECHANICAL POWER IN ROTATING ENGINE Department of Electrical and Electronic Engineering, East West University 9

10 4.2.1 Mechanical Power Electrical Power Adjust Mechanical Power Adjust Electrical Power ENGINE COMPONENTS Engine Main Components General Design Rotation of the Engine COMBUSTION ENGINE Internal Combustion Engine Fuel comes from Burge to Engine BUILD- ON SYSTEM OF ENGINE Fuel System Lubricating Oil System Cooling Water System Starting Air System Exhaust gas and air intake system arrangement Installation Dependent Installation System ENGINE CONTROL SYSTEM MCM (Main Control Module) MAINTENANCES AND SAFETY Maintenances Safety purpose GENERATOR INTRODUCTION CONSTRUCTION OF GENERATOR OPERATION PRINCIPLE OF SYNCHRONOUS GENERATOR Working Principle Direction of Rotation Synchronous Generation on different loading condition Synchronous Generation on different Operation Mode Different Control Mode DESIGN AND DIMENSIONING Automatic Voltage Regulator (AVR) Synchroscope Design Issue SYNCHRONIZATION Condition for Synchronization Worst Case NGR (NEUTRAL GROUNDING RESISTOR) GROUNDING The Objective of Grounding Classification of Grounding GENERATOR MAINTENANCE IR (Insulation Resistance) PI (Polarization Index) Department of Electrical and Electronic Engineering, East West University 10

11 5.9 GENERATOR PROTECTION Differential Protection Over & Under Voltage Protection Over & Under Frequency Protection Over Current Protection Thermal Overload Protection Loss of Excitation Protection Earth Fault Protection BACKUP OR STANDBY GENERATOR PROBLEMS & RECOMMENDATION PROBLEMS RECOMMENDATION CONCLUSION REFERENCE Department of Electrical and Electronic Engineering, East West University 11

12 LIST OF ILLUSTRATIONS Page Figure 2.1: Lightning Arrester. [Source: [1]] Figure 2.2: Capacitive Voltage Transformer.[Source: DBPAL] Figure 2.3: Insulator.[Source: [2]] Figure 2.4: Line Diagram of HV Switchgear..[Source: Author] Figure 2.5: SF6 Circuit Breaker.[Source: [3]] Figure 2.6: Oil Circuit Breaker. [Source: [4]] Figure 2.7: Vacuum Circuit Breaker.[Source: [5]] Figure 2.8: Air Circuit Breaker.[Source: [6]] Figure 2.9: Miniature Circuit Breaker.[Source: DBPAL] Figure 2.10: Molded Case Circuit Breaker.[Source: DBPAL] Figure 2.11: MV switchgear s four panels..[source: DBPAL] Figure 2.12: Incoming from generator panel.[source: DBPAL] Figure 2.13: Outgoing feeder to generator transformer.[source: DBPAL] Figure 2.14: Station Transformer.[Source: DBPAL] Figure 2.15: Metering or measuring.[source: DBPAL] Figure 2.16: External structure of LV Switchgear.[Source: DBPAL] Figure 2.17: Frequency converter.[source: DBPAL] Figure 2.18: Single line diagram of DBPAL (100MW power plant).[source: Author] 32 Figure 2.19: DC system.[source: DBPAL] Figure 2.20: Single line diagram of DC System.[Source: Author] Figure 3.1: Transformer.[Source: DBPAL] Figure 3.2: Dry type transformer (right) and Liquid immersed transformer (left).[source:dbpal] Figure 3.3: Power Transformer Rating Plate in DBPAL.[Source: DBPAL] Figure 3.4: Lightning Impulse Test.[Source: DBPAL] Figure 3.5: HV and LV high voltage test.[source: DBPAL] Figure 4.1: Relation between electrical and mechanical power.[source: DBPAL] Figure 4.2: Engine Block.[Source: DBPAL] Figure 4.3: External structure of an engine.[source: DBPAL] Figure 4.4: Rotation of the Engine.[Source: DBPAL] Figure 4.5: Four Stroke Engine.[Source: [7]] Figure 4.6 Fuel System on Engine.[Source: DBPAL] Figure 4.7: Pressure Regulating Valve.[Source: DBPAL] Figure 4.8: Lubricating Oil flow in Piston.[Source: DBPAL] Figure 4.9: Cooling Water System on Engine.[Source: DBPAL] Figure 4.10: Basic settings of turbo-charging..[source: DBPAL] Department of Electrical and Electronic Engineering, East West University 12

13 Figure 4.11: Flywheel.[Source: DBPAL] Figure 5.1: Stator (left) and Rotor (right).[source: DBPAL] Figure 5.2: Parts of Generator. [Source: DBPAL] Figure 5.3: Faraday s Law of Induction.[Source: DBPAL] Figure 5.4: Voltage Control Mode.[Source: DBPAL] Figure 5.5: Auto (left) and Manual (right).[source: DBPAL] Figure5.6: Speed droop control (left) & True kw control (right).[source: DBPAL] Figure 5.7: Schematic diagram of AVR.[Source: DBPAL] Figure 5.8: Synchroscope.[Source: DBPAL] Figure 5.9: Meters for synchronization.[source: DBPAL] Figure 5.10: Phase Sequence.[Source: DBPAL] Figure 5.11: Synchronization of frequency.[source: DBPAL] Figure 5.12: Worst Case.[Source: DBPAL] Figure 5.13: NGR. [Source: [8]] Figure 5.14: Grounding.[Source: DBPAL] Figure 5.15: VAMP 210 (left) and Biased Differential Relay (right).[source: DBPAL]83 Figure 5.16: Neutral Over Current Protection. [Source: DBPAL] LIST OF TABLES Page Table 3-1: Transformer Rating in DBPAL Table 5-1: Modes of Operation Department of Electrical and Electronic Engineering, East West University 13

14 1. INTRODUCTION In the Spring semester of 2012 we got the opportunity of doing internship in Dutch Bangla Power & Associations Ltd (DBPAL). We started our internship on 26 December 2011 and completed on 12 January From DBPAL we have gathered practical experience over power generation process, power generating equipments protection and power distribution system. Before this internship we had only theoretical knowledge over these topics but on completion of internship in DBPAL we had the opportunity to experience the process of power generation, switchgear protection and power distribution system and got the chance to observe the industrial environment. DBPAL started on 20 th July It is a heavy fuel power plant, basically use furnace oil. The total capacity of DBPAL is 100MW which is generated by 12 units. Each unit produces 8.9MW. The owner of the DBPAL is Orion Group but the maintenances and operations are done by WARTSILA Bangladesh. 1.1 Company Profile Name of the Company: Dutch Bangla Power & Associates Ltd (DBPAL). Starting Date: 20 th July Location: Ailpara, Siddhirganj, Narayanganj on the bank of the river Shitalakkha Installed Capacity: MW Supply to PDB: 100MW Total Number of Units: 12 The owner of the DBPAL is Orion Group but the maintenances and operations are done by WARTSILA Bangladesh. Wartsila is a Finish Company which is the biggest manufacturer of engine. Wartsila took the responsibility of operations & maintenances for 5 years. They started their journey at 20 th July Here in the power plant there are 12 units, each generates 8.9MW & supplies to PDB a total of 100MW. Department of Electrical and Electronic Engineering, East West University 14

15 1.2 Objective of the Internship The first objective is to complete EEE499 course which is an essential part of completing Bachelor in EEE at EWU. Before doing this internship we had only theoretical knowledge over these topics but on completion of internship in DBPAL we have earned practical knowledge also. The following list summarizes our internship goals. Understanding company management. Understanding industrial environment. Acquiring practical knowledge about power generation Acquiring practical knowledge about switchgear protection. Idea about safety 1.3 Scope and Methodology Scope This report is based on the internship program where we reviewed the basic process of power generation, switchgear protection, power distribution and substation of DBPAL. It also contains descriptions of various mechanical and electrical equipments which are used to generate and distribute power in DBPAL. The report contains other relevant information about the DBPAL which we observed during the internship program Methodology Department of Electrical and Electronic Engineering, East West University 15

16 We have organized our report mainly in two subsections: Power Distribution and Power Generation. In power distribution part there are switchgear and transformer. And power generation it consists of engine and generator. This report has been prepared on the basis of: Primary information: The information is gathered by personal observation and working with the plant engineers at DBPAL. Secondary information: The company website and various single line diagrams provided by the engineers whom we worked with. Department of Electrical and Electronic Engineering, East West University 16

17 2. SWITCHGEAR 2.1 Introduction In the switchgear section we spent four days, from 26 December 2011 to 28 December 2011 and 30 December In this section we have come to know from DBPAL about switchgear, the types of switchgear, different types of circuit breaker, four panels, and single line diagram of DBPAL etc. A great demand for electrical energy is a notable feature of modern civilization. Electrical Energy Measurement system ensures supply of energy to every consumer at all times at rated voltage, rated frequency and specified wave form, at lowest cost and with maximum environmental degradation. For this purpose, means must be provided to switch on or off generators, transmission lines, distributors and other equipment under both normal and abnormal conditions. This is achieved by an apparatus called switchgear. It is essentially consists of switching and protecting devices such as switches, fuses, circuit breakers, relays etc. 2.2 Switchgear The apparatus used for switching, controlling and protecting the electrical circuits equipments is known as switchgear. This is used in association with the electric power system, or grid. Fuses or circuit breakers are usually employed to protect the system during maintenance or faulty condition. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. In the Dutch Bangla Power & Association Limited (DBPAL) we have learnt the importance of this protection because the reliability of the operation depends on this system Classification In the Dutch Bangla Power & Association Limited (DBPAL) at switch gear section we studied circuit breakers, relays, control panels etc. We studied the classification of switchgear by voltage. So we can divide the switchgear section in 3 parts on the perspective of DBPAL: By voltage class: High voltage (35kV 230kV AC) Department of Electrical and Electronic Engineering, East West University 17

18 Medium voltage (1,000 35,000 volts AC) Low voltage (100-1,000 volts AC) DC system 2.3 High Voltage (HV) Switchgear High voltage switchgear which is applied for power control and distribution systems of AC 50Hz, has rated working voltage up to 132kV. The essential components in HV switchgear of DBPAL are: Lightning Arrester Capacitive Voltage Transformer (CVT) Insulator Isolator (earthing switch is connected) Current Transformer (CT) Circuit Breaker Busbar Transformer Inductive Voltage Transformer (IVT) Lightning Arrester The lightning arrester found in DBPAL is a device used to protect the insulation on the system from the damaging effect of lightning. The equipment connected between the conductor and ground to discharge the excessive voltage to earth. Lightning arrester operates in µs. There is a counter in lightning arrester. In lightning there is an air gap so, it works as a simple conductor. Department of Electrical and Electronic Engineering, East West University 18

19 Figure 2.1: Lightning Arrester. [Source: [1]] Capacitive Voltage Transformer (CVT) In DBPAL, we learnt that the capacitive voltage transformer (CVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitor across which the transmission line signal is split, and inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. The upper side of the CVT is known as the carrier and middle part is made by porcelain where operation procedure runs. Figure 2.2: Capacitive Voltage Transformer.[Source: DBPAL] Department of Electrical and Electronic Engineering, East West University 19

20 2.3.3 Insulator An insulator is a material that does not respond to an electric field and completely resists the flow of electric charge. In DBPAL we came to know that in practical life, perfect insulator does not exist. Therefore, dielectric materials with high dielectric constants are considered as insulators. Figure 2.3: Insulator.[Source: [2]] Isolator In DBPAL we found that an isolator is a switch that does not have arc interruption capability. It is always operated in off-load. If we want to switch on the isolator then we have to make sure no current is flowing. Isolator is required for maintenance purpose and to isolate the circuit. Isolators are placed before and after of circuit breaker in series at high voltage switchyard. Figure 2.4: Line Diagram of HV Switchgear..[Source: Author] Department of Electrical and Electronic Engineering, East West University 20

21 2.3.5 Busbar In electrical power distribution, a busbar is a strip of copper or aluminum that conducts electricity within a switch board, distribution board, substation or other electrical apparatus. In DBPAL there is no over current protection system is given in busbar Current Transformer (CT) In DBPAL we saw that the ratio of current transformer is generally high (600:1). The voltage ampere capacity is low as compared with that of power transformer. In current transformer, no additional voltage is applied. Because in primary and secondary side voltage are same Circuit Breaker A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. We found in DBPAL that, for low voltage level (100-1k) V, Molded Case Circuit Breaker (MCCB), Miniature Circuit Breaker (MCB), and Air Circuit Breaker (ACB) are used. For medium voltage (1k-35k) V, Vacuum Circuit Breaker (VCB), SF6 Circuit Breaker, and Oil Circuit Breaker (OCB) are used. For high voltage (35k-230k) V, Air Blast Circuit Breaker (ABCB), SF6 Circuit Breaker, and Oil Circuit Breaker (OCB) are used a Air Blast Circuit Breaker (ABCB) This type of breakers in DBPAL employs air blast as the quenching medium. The contacts are opened by air blast produced by the opening of blast valve. The air blast cools the arc and sweeps away the arcing products to the atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc. Consequently the arc is extinguished and the flow of current is interrupted. Department of Electrical and Electronic Engineering, East West University 21

22 2.3.7b SF6 Circuit Breaker We have seen in DBPAL that in this circuit breaker, sulphur hexafluoride (SF6) gas is used as the arc quenching medium. The SF6 gas is an electro negative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of SF6 gas and an arc is struck between them. The conducting free electrons in the arc are rapidly captured by the gas to form relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the arc. This circuit breaker is very effective for high power and high voltage service. Figure 2.5: SF6 Circuit Breaker.[Source: [3]] 2.3.7c Oil Circuit Breaker (OCB) In DBPAL we have seen that, in oil circuit breakers insulating oil is used as an arc quenching medium. The contacts are opened under oil and an arc is struck between them, heat of the arc evaporates the surrounding oil and produce hydrogen at high pressure. The oil is pushed away from the arc region and the gas bubble occupies adjacent portions of the contact. The arc extinction is facilitated mainly by two processes. Firstly the hydrogen gas has high heat conductivity and cools the arc, thus aiding the deionization of the medium between the contacts. Secondly the gas sets up turbulence in the oil and forces it into the space between contacts thus eliminating the arcing products from the arc path resulting in arc extinction and interruption of current. Department of Electrical and Electronic Engineering, East West University 22

23 Figure 2.6: Oil Circuit Breaker. [Source: [4]] 2.3.7d Vacuum Circuit Breaker (VCB) In DBPAL vacuum circuit breakers are used to protect medium and high voltage circuits from dangerous electrical situations. Like other types of circuit breakers, vacuum circuit breakers literally break the circuit so that energy cannot continue flowing through it. In a vacuum circuit breaker, two electrical contacts are enclosed in a vacuum. One of the contacts is fixed, and the other is movable. When the circuit breaker detects a fault, the movable contact pulls away from the fixed contact, interrupting the current. Because the contacts are in a vacuum, arcing between the contacts is suppressed, ensuring that the circuit remains open. As long as the circuit is open, it will not be energized. Rated voltage is 22kV -66kV and rated current is 2500A-3150A. Figure 2.7: Vacuum Circuit Breaker.[Source: [5]] Department of Electrical and Electronic Engineering, East West University 23

24 2.3.7e Air Circuit Breaker (ACB) Air circuit breakers can be used both as circuit-breakers for general protection and as protection circuit breakers of electrical machines. It is available from 400A to 6400A. Under Voltage Release mechanism is used in this circuit breaker. In DBPAL, we know that this mechanism will be activated when there will be low voltage supply or zero voltage supply. Magnetic tripping mechanism applied for short circuit. Figure 2.8: Air Circuit Breaker.[Source: [6]] 2.3.7f Miniature Circuit Breaker (MCB) Rated current of MCB is not more than 100 A. It can be used for both single phase and three phase power system. The tripping characteristic is not adjustable normally. Thermal or thermal magnetic mechanism is used in this circuit breaker. There is no fixed time for the thermal operation. Figure 2.9: Miniature Circuit Breaker.[Source: DBPAL] Department of Electrical and Electronic Engineering, East West University 24

25 2.3.7g Molded Case Circuit Breaker (MCCB) We have seen in DBPAL that the rated current of Molded Case Circuit Breaker is up to 2500 A. It has also thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings using a knob. Normally it is used for three phase power system. Figure 2.10: Molded Case Circuit Breaker.[Source: DBPAL] 2.4 Medium Voltage (MV) switchgear MV switchgear distributes electric power from generators to step-up transformers for grid connection and station transformers for internal consumption. MV switchgear is used for the safety of breaker and alternator. In MV switchgear the breaker type is SF6 and vacuum. From DBPAL, we know that the manufacturers of MV switchgear are ABB & Uni-power. The nominal voltages are 12kV, 17.5kV, 24kV. The nominal currents are ( ) A & ( ) A. The Short circuit withstand currents are 40 ka 3s & peak currents 100 ka. Arc withstand are 40 ka. The construction of MV switchgear is metal-clad or cubicle type. In DBPAL we know that there are different cubicles or panels of MV switchgear. These are Generator breakers Station transformer breakers Feeder breakers Bus tie breakers Measuring Department of Electrical and Electronic Engineering, East West University 25

26 In DBPAL, these cubicles are bolted together for rigid and solid construction. There is a mechanical interlocking system for safe operation. There present different compartments for different circuits. In the Dutch Bangla Power & Association Limited (DBPAL) at MV switchgear section we have seen there are 4 panels. These are Incoming from generator Outgoing feeder Station transformer Metering or measuring Bus tie breaker is not there because there is no interconnection between the buses. Figure 2.11: MV switchgear s four panels..[source: DBPAL] Incoming from generator In the incoming from generator panel, there is a 0-CT transformer behind the voltage transformer. 0-CT transformer works in balance condition. In unbalanced condition it will trip. In DBPAL, the shape of the 0-CT transformer is square and the wires go to the generator. Department of Electrical and Electronic Engineering, East West University 26

27 Figure 2.12: Incoming from generator panel.[source: DBPAL] Outgoing feeder to generator transformer In DBPAL, the outgoing feeder to generator transformer there is an active power (KW), reactive power (KVAR) & current transducer. A current transducer is a device that converts one form of energy to another. Energy types include electrical, mechanical, electromagnetic, chemical or thermal energy. It is widely used in measuring instruments. Here the transducer rating is (4-20) ma. Figure 2.13: Outgoing feeder to generator transformer.[source: DBPAL] Station transformer (1600KVA) In the station transformer, there is a voltage and current transducer, thermostat, PLC and magnetic conductor. Department of Electrical and Electronic Engineering, East West University 27

28 2.4.3a Thermostat A thermostat is the component of a control system which regulates the temperature of a system so that the systems temperature is maintained near are desired set point temperature b Programmable Logic Controller (PLC) A PLC (Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at inputs and depending upon their state, turning on/off its outputs. Figure 2.14: Station Transformer.[Source: DBPAL] Metering or measuring panel In DBPAL we found that the measuring cubicle is only used for measuring, no breaker installed. In the down compartment, there are current transformers and voltage transformers. In the top compartment there are control circuits, connectors, relays and auxiliary equipment, & protection relays. Only in this panel frequency transducer exists. Department of Electrical and Electronic Engineering, East West University 28

29 Figure 2.15: Metering or measuring.[source: DBPAL] There are three (3) compartments in the MV switchgear. These are Control & monitoring Breaker Cable connections and Transformers In DBPAL, the protection and measuring for MV switchgear s are: In the busbars there are over / under voltage protection, over / under frequency protection, voltage measuring, frequency measuring, and current measuring. In the feeder and bus-tie breakers there are over current protection, earth fault current protection, voltage / current measuring, and active / reactive power measuring. 2.5 Low Voltage (LV) switchgear The Low Voltage switchgear can be called the station service switchgear since it serves all the auxiliary power needs, such as motors (pumps), fans, heaters, complete units etc consumers. To run auxiliary system LV switchgear is needed. In DBPAL, LV switchgear distributes power from station transformers to auxiliary units and power plant s internal network. Manufacturer of LV switchgear are ABB and Uni-power. In DBPAL, the maximum rated voltage of LV switchgear is 690V and rated currents are from A. Short-circuit withstand busbars is ka. The modular structure of LV switchgear, delivery in parts, modules bolted together for rigid construction, each compartment providing power for different units. Department of Electrical and Electronic Engineering, East West University 29

30 The layouts of LV switchgear in DBPAL are given below: Aluminium plates Compartments Ducts for cable distribution Compartment separation Efficient air circulation Arc pressure directed away to the rear Busbars with insulators Different dimensions of compartments Cubicles bolted together; can make up single free standing units Units can be positioned in different places around the power plant according to design Figure 2.16: External structure of LV Switchgear.[Source: DBPAL] The compartments of LV switchgear in DBPAL are given below: Standard structure Withdraw able structure Both structures equipped with necessary breakers and meters Each compartment dimensioned according to needed output Department of Electrical and Electronic Engineering, East West University 30

31 2.5.1 Frequency converter In DBPAL Frequency converters are used in order to facilitate an accurate control of critical processes, such as: Cooling system (radiators, pumps) Fuel system (booster, heater) Ventilation (engine hall ventilation) The frequency converter is also an energy saver and in many applications also noise limiter. Figure 2.17: Frequency converter.[source: DBPAL] 2.6 Single line diagram Single line diagram is a simplified notation for representing a three-phase power system. Electrical elements such as circuit breakers, transformers, isolators, bus bars, generators and neutral grounding resistor (NGR) are shown by standardized schematic symbols. Instead of representing each of three phases with a separate line or terminal, only one conductor is represented. Figure 2.18 shows the single line diagram of 100MW power plant and each generator capacity is 8.9MW. We have shown only four units or generators instead of 12 units. Department of Electrical and Electronic Engineering, East West University 31

32 Figure 2.18: Single line diagram of DBPAL (100MW power plant).[source: Author] 2.7 DC system The DC system is used to convert the AC supply into DC supply to the equipment needing DC power. Normally the DC power is supplied through rectifiers through the battery package as backup in case of supply failure. In DBPAL, the DC system consists of a free standing cubicle including chargers (rectifiers), batteries and distribution. Normally the rectifier supplies the load. The battery bank supplies the load for a limited time if the mains supply is interrupted. Department of Electrical and Electronic Engineering, East West University 32

33 Figure 2.19: DC system.[source: DBPAL] The DC system shall provide 110V DC, 10% to the consumers in the power plant. The batteries are typically sized for 6 or 10 hours. There are two types of batteries Lead acid or Nickel- Cadmium where lead acid is preferred. In DBPAL, there are 9 batteries in each DC system. Each carries 12V. 9*12unit=108V but DC systems provides 110V. Figure 2.20: Single line diagram of DC System.[Source: Author] 2.8 Voltage and current levels In DBPAL, there are some voltage and current levels for the equipments of the substation. These levels are described below Rated current levels There are some rated current levels in DBPAL for the equipments. These are mentioned below. Department of Electrical and Electronic Engineering, East West University 33

34 2.8.1a Rated normal current Rated normal current is the r.m.s value of the current which the equipment shall be able to carry continuously. Here the r.m.s value is 600A b Rated short time withstand current Rated short time withstand current is the r.m.s value of the current which the equipment can carry in closed position during a specified short time 1s or 3s c Rated peak withstand current Rated peak withstand current is the peak current associated with the first major loop of the rated short time with stand current which the equipment can carry in closed position. The standard value is 2.5 times the rated short time withstand current for HV and times the rated short time withstand current for LV systems d Rated short circuit breaking current The rated short-circuit (breaking) current is the maximum symmetrical short-circuit current in ka rms, which a circuit breaker shall be capable of breaking. Two values are related to the rated short-circuit current, these are the rms value of the a.c. component and the percentage d.c. component e Rated short circuit making current The rated short-circuit making current indicate the maximum peak current the circuit breaker shall be able to close and latch against. Normally making current is higher than breaking current Voltage levels In DBPAL, we have seen the voltage level is generally defined with two values. These are nominal voltage level and high voltage level a Nominal voltage level Nominal voltage level is the voltage level by which a system or equipment is designated and to which certain operating characteristics are referred. Here nominal voltage level is 132 kv. Department of Electrical and Electronic Engineering, East West University 34

35 2.8.2b High voltage level The system is specified regarding insulation and other characteristics which may be referred to this highest voltage in the relevant equipment recommendations. Here high voltage level is 145kV. Department of Electrical and Electronic Engineering, East West University 35

36 3. TRANSFORMER 3.1 Introduction In the transformer section in DBPAL we have spent only one day, 6 th Jan In this section we have come to know from DBPAL about the construction of transformer, types of transformer, operation criteria, types of transformer testing, maintenance and protection of transformers etc. Transformer is a static device which transforms A.C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction. It is the basic and most important part of Power transmission system. In Dutch Bangla Power and Associates Ltd (DBPAL) different types of transformer is used. There are many types of transformer, beside them potential transformer, current transformer and distribution transformer is most significant. Figure 3.1: Transformer.[Source: DBPAL] 3.2 Construction of Transformer In DBPAL, we have seen that a transformer consists of: Main Tank Radiators Conservator Explosion Vent Lifting Lugs Air Release Plug Department of Electrical and Electronic Engineering, East West University 36

37 Oil Level Indicator Tap Changer Wheel HV/LV Bushings Filter Valves Oil Filling Plug Cable Box Silica Gel (if there is a moisture or water in the air silica gel absorbs it) Transformers are used in distribution networks in order to: minimize energy losses, minimize voltage drops and ensure electrical separation between networks. Transformers are mainly outdoor, oil cooled, 3-phase, 50HZ. Here, primary is delta connected and secondary is star connected. It is naturally cooled (ONAN type). The standard voltage rating is 11kV/415V. In the transformer input is 11kV and output is 415V. 3.3 Types of Transformers In power system many types of transformer is available. Among them Dutch Bangla Power and Associates Ltd (DBPAL) uses mainly Distribution Transformers, Power Transformers, Current Transformer (CT), Potential Transformer (PT), Booster Transformer, Rectifier Transformer, Phase-shifting Transformer, Welding Transformer and High Voltage Testing/ Short Circuit Testing Transformer. Mainly there are two types of transformers. These are: Dry type transformers Liquid immersed transformers Dry Type Transformers In controlled environment this type of transformers are normally used. It has a good fire resistant behavior. It treated windings to resist moisture, sea-air, and oil vapors. The cost of this type of transformer is very high. Department of Electrical and Electronic Engineering, East West University 37

38 Figure 3.2: Dry type transformer (right) and Liquid immersed transformer (left).[source:dbpal] Liquid Immersed Transformers We have seen in DBPAL, that this type of transformer is normally sealed, liquid is nonflammable. It is suitable for unsupervised installation (no maintenance). It is equipped with breathing device trapping moisture from entering into the insulating liquid and with liquid gauge. It has accidental leakage arrangement. Oil filled transformers are typically used for equipment deliveries. The advantage with Oil transformers are: it can be placed outside and it is slightly less expensive. Here, both oil and winding temperature detection is needed. In DBPAL Liquid immersed transformers is used. Table 3-1: Power Transformer Rating in DBPAL Rating Description 40/50 MVA Transformer rating ONAN/ONAF Oil Natural Air Natural/ Oil Natural Air Force 140V/11kV It should be fixed 11kV at secondary side though there may be voltage change in primary side at loaded condition. By tap changer we can change voltage at primary side. Department of Electrical and Electronic Engineering, East West University 38

39 +/- 15% Grid voltage can fluctuate up to +/- 15% Z= 12.0% Z denotes percentage impedance. By using it we can calculate earth fault and short circuit calculation. YNd11 Y= star connected at primary side N= neutral grounded D= delta connected at secondary side 11= phase difference between primary and secondary side 3.4 Operation Criterions There are some operation criterion of a transformer we have found in DBPAL. These are mentioned below. Parallel operation Compatible coupling groups and voltage regulation ensuring equal load sharing Voltage regulation Maximum 2.5% voltage drop from no load to full load at resistive load Short circuit withstand Time limited (1s) Enclosure Complying with IP protection requirements Rating plate Information about make, type, performance values etc. Department of Electrical and Electronic Engineering, East West University 39

40 Figure 3.3: Power Transformer Rating Plate in DBPAL.[Source: DBPAL] Transformers are tested by manufacturer and are documented Temp rise test, Insulation resistance, Voltage ratio, Winding resistance. 3.5 Overloads of Transformers Generally an overload will increase the temperature of the windings and can possible damage the insulation. During our internship in DBPAL we have come to know that overloads usually generates from other part of the system, low voltage side or high voltage side. Local conditions (ambient temperature) can have an effect on the amount of overload. Both low voltage distribution networks and high voltage distribution networks usually have protection devices to limit possible under / over voltage, current and frequency and force breakers to open thereby disconnecting circuits and also transformers. It is however common that also transformers have protection devices. 3.6 Faults that can occur In DBPAL, we have found that there can be certain faults occur in a transformer. These faults are discussed below. Department of Electrical and Electronic Engineering, East West University 40

41 3.6.1 Faults between MV winding turns From DBPAL we came to know that this is the most frequent fault in the transformer. It is caused due to thermal or dielectric stresses and difficult to detect Faults between LV windings Our mentor in DBPAL said that, this fault is usually exceptional since these windings are placed closest to the core and are surrounded by MV windings. In case of multiple LV windings on the same magnetic core column (zigzag coupling) there exists a possibility of fault. Progression can be rapid due to the presence of an arc of significant intensity Faults between MV and LV windings This fault occurs between windings can also lead to a contact between primary and secondary sections. This will lead to the appearance of a dangerous potential on the low voltage side Faults between MV windings and earth This fault usually originates from a break in insulation due to over voltage. This can also be a result of mechanical type faults Other examples of faults and results From DBPAL, we came to know that there also some other faults that can occur in a transformer. These are mentioned below: Over voltage It is caused by network switching, lightning strikes. It can cause breakdowns between winding turns and windings and earth. Signs can be smoke release, slight increase in currents, earth-fault currents Over currents during operation It is caused by overloads and faults on low voltage network. It can destruct windings at hot spots by short-circuiting winding turns. Signs can be smoke release or slight increase in currents. Department of Electrical and Electronic Engineering, East West University 41

42 High over current It can be caused by nearby fault in low voltage network. It can destruct windings at hot spots by short-circuiting winding turns. Signs are quick and random progression towards a fault between windings. Ageing It is caused by cumulative effects of past faults. It can cause breakdown between MV winding turns. Signs can be smoke release, increase of currents and earth-faults. 3.7 Testing of transformers DBPAL uses three types of tests for transformers. These are given below: Type Test Special test Routine Test Type Test In DBPAL, there are two type tests. These are Lightning Impulse Test and Temperature rise test. The purpose of lightning impulse test is to confirm that the transformer insulation withstands the lightning over voltages which may occur in service. The Power Transformers used in high voltage systems at any time may be affected by the atmospheric discharges. The magnitudes of the lightning over voltages always depend on the impulse current and impulse impedance where the lightning impulse occurs. This value is several times of operating voltage. In the transformer, maximum seven times greater voltage is applied to check its insulation. Department of Electrical and Electronic Engineering, East West University 42

43 Figure 3.4: Lightning Impulse Test. [Source: DBPAL] Special Test From DBPAL we have come to know that, this test measures the ability of the transformer to withstand the mechanical and thermal stresses caused by the external short circuit. The following tests are under Special Test. Additional Impulse test Short circuit test Measurement of zero Phase sequence Impedance test Measurement of harmonics of the no load current test Magnetic balance test Routine Test Routine test is the most important test for the transformer. From DBPAL we came to know that there are many types of tests under routine test. These are given below: 3.7.3a Measurement of winding resistance Test This test measures the resistance of the HV & LV winding. The values of resistance should be balance for all three phases and should match the designed values. This type of test is used in Digital resistance meter. Department of Electrical and Electronic Engineering, East West University 43

44 3.7.3b Measurement of insulation resistance Test In DBPAL, this test measures the insulation resistance of HV & LV windings with respect to earth (body) and between LV & HV winding. Megger test is beyond under this test c Separate source voltage withstand test (High Voltage tests on HV & LV) In DBPAL, this test checks the insulation property between Primary to earth, Secondary to earth and between Primary & Secondary. HV high voltage test LV winding connected together and earthed. HV winding connected together and given 28 KV (for 11KV transformer) for 1 minute. Figure 3.5: HV and LV high voltage test.[source: DBPAL] LV high Voltage test HV winding connected together and earthed. LV winding connected together and given 3 KV for 1 minute. It is used in High Voltage tester (100KV & 3KV) Department of Electrical and Electronic Engineering, East West University 44

45 3.7.3d Induced Over voltage Withstand test (DVDF test) In DBPAL, this test is used in motor generator set. For an 11KV/433V transformer, 866 Volts are applied at the 433V winding with the help of a Generator for 1 minute e Measurement of No Load Loss & Current Test We have found in DBPAL, that the iron losses and no load current are measured in this test. The 433V winding is charged at 433V supply & the 11KV winding is left open.the power consumed by the transformer at no load is the no load loss in the transformer. 3.8 Maintenance and Protection of Transformer Maintenance and protection of a transformer is very essential, because transformer plays a significant role in power system Maintenance We have come to know during our internship in DBPAL that, transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization. The maintenance factors of a transformer are given below: 3.8.1a Oil Our mentor said in DBPAL that, oil level must be checking and oil acidity checking at regular intervals. If acidity is between 0.5 to 1mg KOH, oil should be kept under observation. Insulation resistance of the transformer should be checked once in 6 months. Megger values along with oil values indicate the condition of transformer b Bushing Bushings should be cleaned and inspected for any cracks. Dust and dirt deposition, Salt or chemical deposition, cement or acid fumes depositions should be carefully noted and rectified. Transformer should be continuously checked of any loose connections of the terminations of HV & LV side. Conservator should be cleaned from inside after every three years. Oil & Winding temperature meter readings should be regular checked. Substation yard should be cleaned. Department of Electrical and Electronic Engineering, East West University 45

46 3.8.2 Protection From DBPAL, we came to know that, the best way of protecting a transformer is to have good preventive maintenance schedule. For protection, a transformer should have oil Temperature Indicators, Winding Temperature Indicators, Buchholz Relay, Magnetic Oil Level Gauge, Explosion Vent, HT fuse, LT circuit breaker, HT Circuit breaker with Over load, Earth Fault relay tripping, Oil Surge Relay, Lightening Arrester and Breather. Transformer protection is a branch of electrical power engineering that deals with the protection of electrical power systems from faults through the isolation of faulted parts from the rest of the electrical network. Department of Electrical and Electronic Engineering, East West University 46

47 4. ENGINE 4.1 Introduction In the engine section in DBPAL we have spent 5 days, from 8 January 2012 to 12 January In this section, we have come to know from DBPAL about the construction of engine, mechanical power in engine, and build on system of engine, operation criteria, testing of engine and protection of engine etc. An engine or motor is a machine designed to convert mechanical energy into electrical energy. Heat engines, including internal combustion engines and external combustion engine (such as steam engines) burn a fuel to create heat which is then used to create motion. A machine which produces power by burning fuel in body of air which has been squeezed to a high pressure by a moving piston is called an engine. 4.2 Mechanical Power in Rotating Engine In rotating engine, mechanical and electrical power is very necessary Mechanical Power Power in mechanical systems is the combination of forces and movement. In particular, mechanical power is the product of a force on and objects and the objects velocity, or the product of a torque on a shaft and the shaft angular velocity. P = ω T T = torque Where, ω=2 π n ω = angular speed, rad/s In this equation 2 and π are constants by nature and the n (speed) we want to keep as constant as possible. The goal off course is to stable grid frequency (50 or 60 Hz) which leads to the stable engine speed (rpm >>1/s). Department of Electrical and Electronic Engineering, East West University 47

48 4.2.2 Electrical Power Electrical power is combination of two ingredients, Active Power and Reactive Power. Active Power, P Active power is the power which does the actual work, rotating, heating, lightning etc. Its unit is kw. Reactive Power, Q Reactive power is the power which is needed for the excitation of different coils, motors, transformers etc. Its unit is kvar. The result of P and Q is known as apparent power Adjust Mechanical Power To adjust mechanical power some objects are much needed. These are torque, pressure and force. Torque Torque is the power with which the piston turns the crankshaft and so rotates the engine. It is the parameter which controls the power of the rotating machine. Torque is force multiplied by the length of the arm (stroke/2) T = Fl Torque can be adjusted by adjusting the pressure over the piston and that s adjusted by the amount of fuel and the timing of combustion. Pressure Area of the piston and the length of the stroke is up to the design, pressure is the only thing which we can adjust while running the engine. Force A force is any influence that causes and objects to undergo a change in speed, a change in direction or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity (which includes to begin moving from a state of rest) to accelerate or which a can cause a flexible object to deform. F = pa, force is pressure multiplied by area Department of Electrical and Electronic Engineering, East West University 48

49 Force can also describe by intuitive concepts such as a push or pull Adjust Electrical Power The active power (P) is generated by the prime mover which leads us to the conclusion that it has to be controlled by the prime mover. Reactive power (Q) is really generated by the generator in accordance of load and excitation. (Excitation being the way of adjusts the generator.). Voltage is part of the electrical power which has to be controlled also, depending onf the system; it s either controlled by the grid or by the generator control (AVR, automatic voltage regulator). Figure 4.1: Relation between electrical and mechanical power.[source: DBPAL] When producing electrical power with the rotating engine, the engine has to be able to produce the active power (P). 4.3 Engine Components Engine basically built by some components which are very necessary for an engine, these components are given below Engine Main Components The main components of engine are Engine Block, Oil Sump, Crankshaft, Piston, Camshaft, Valve Mechanism, Cylinder Head, Intake and Exhaust Manifolds. Department of Electrical and Electronic Engineering, East West University 49

50 Engine Block The engine block is made of cast iron in one piece. The block has been given a stiff and durable design to absorb internal forces. It works as a frame, where the most of the other components are mounted on. The main bearing caps are fixed by hydraulically tightened screws. A combined flywheel or thrust bearing is located at the driving end of the engine. Main Components of Engine Block s are Main bearing cap, Main bearing shell upper, Lateral tie screw, Thrust bearing rail, Camshaft bearing bush and Intermediate shaft bearing bush. Figure 4.2: Engine Block.[Source: DBPAL] Crankshaft The reciprocating motion of the pistons and the connecting rods are converted into a rotating motion of the crankshaft. The power of the engine can then be taken out to the application through a powerful connection at the crankshaft. Piston The piston conveys the energy coming from the combustion of the fuel to the connecting rod. Due to the explosion in the combustion chamber the piston is pushed down and the motion is transferred to the crankshaft by the connecting rod. The piston is of a composite type with a nodular cast iron skirt and a forged steel crown. The space between the crown and the skirt is supplied with lubricating oil for cooling of the crown by means of a cocktail shaker effect. Department of Electrical and Electronic Engineering, East West University 50

51 Camshaft The camshaft is connected to the crankshaft by gear or chain and rotates at half the crankshaft speed, as it rotates the cams come under the valve push rod and lift the valves. Cylinder Head Cylinder head which closes the top end of the cylinder, so as to make a confined space in which to compress the air and to confine the gases, while they are burning and expanding. Intake and Exhaust Manifolds The exhaust manifold is provided with flexible expansion bellows to eliminate forces caused by thermal deformation. The bellows are fitted to the pipes with screws and sealed with sealing rings. These are the main component of engine however there are also some components like bearing, crank, spray nozzle or fuel injector, combustion and heat exchanger General Design In engine there two type temperatures are being maintained. These are low temperature and high temperature Low temperature (LT) In the LT side lube oil temperature are being maintained and the temperature is (60-65) C. To heat up the lube oil we have to give hot water and the temperature of water should be (40-42) C. There are two types of cooling system in LT side. Lube oil cooler and charge air cooler. High temperature (HT) Here temperature is 96 C. There are two types of cooling system in HT side. Jacket cooler and charge air cooler. The higher temperature is converted to a 4-20 ma analogue signal and used for local indication of HT water temperature. Department of Electrical and Electronic Engineering, East West University 51

52 Figure 4.3: External structure of an engine.[source: DBPAL] Rotation of the Engine Direction of the engine shaft rotation is viewed from the driving end. It can be clockwise rotation (rotation to the right) or counter clockwise rotation (rotation to the left). The driven equipment of engine is also viewed from its shaft end. Consequently, a clockwise rotating engine is coupled to a counter clockwise rotating alternator. Figure 4.4: Rotation of the Engine.[Source: DBPAL] 4.4 Combustion Engine Combustion is that kind of chemical reaction that is accompanied by the release of considerable light and heat. There are two type of combustion engine, internal and external. Department of Electrical and Electronic Engineering, East West University 52

53 4.4.1 Internal Combustion Engine Combustion is that kind of chemical reaction that is accompanied by the release of considerable light and heat. There are two type of combustion engine, internal and external. The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and high pressure gases, which are produced by the combustion, directly applies force to components of the engine, such as the pistons or turbine blades or a nozzle, and by moving it over a distance, generates useful mechanical energy a Four Stroke System Four stroke systems have four stroke cycles. These are Suction, Compression, Expansion and Exhaust. Suction stroke To start with the piston is at or very near, the inlet valve is open and the exhaust valve is closed. A rotation is given to crank by the energy from a fly wheel or by a starter motor when the engine is just being started. As the piston moves from top bottom dead centre the rarefaction is formed in the cylinder that is the pressure in the cylinder is reduced to a value below the atmospheric pressure. Compression stroke Both the valves are closed and piston moves from bottom to top dead centre. The air is compressed up to a compression ratio that depends upon the type of the engine. For diesel engines the compression ratio is 12/18 and the pressure and temperature at the end of compression respectively 35-40kg/cm 2 and C. Department of Electrical and Electronic Engineering, East West University 53

54 Figure 4.5: Four Stroke Engine.[Source: [7]] The power stroke includes combustion of fuel and expansion of the products of combustion. The combustion of charge commences when the piston approaches in the petrol engines, the charge is ignited by causing an electric spark between the electrodes of a spark plug which is located somewhere in the walls of combustion chamber. Exhaust stroke The exhaust valve begins to open when about power is complete. A pressure of 4-5 kg/cm 2 at this instant forces about 60% of the burnt gases into the exhaust manifold at high speed. Much of the noise associated with automobile engines is due to high exhaust velocity Fuel comes from Burge to Engine Fuels are substances which can be burned to produce thermal energy. Fuels are essential for obtaining heat, for operating gas turbines & IC Engines for producing electric energy in central power plants for Chemical process etc. Storage Tank When Burge comes, the Burge pump and unloading pump should be on. Fuel will be stored at the storage tank. Here the temperature is (30-35) C. Department of Electrical and Electronic Engineering, East West University 54

55 Buffer Tank/ Settling Tank Fuel comes to Buffer Tank from Storage Tank. Here oil s are being settled. If any water present in the oil, this tank separates the water from the oil. Here the temperature is (60-65) C. Fuel Treatment Unit Here, oil s are being purified. In this unit, there present a separator, feed pump and motor. Motor is used for power consumption. Here the temperature is 95 C. Service Tank/Day Tank Here the temperature is (85-90) C. Supply Pump & Booster Pump In the supply pump, output pressure is 5.5 bar. & in the booster pump, output pressure is 8-10 bar. Engine Finally fuel goes to engine and mechanical energy converts to electrical energy. 4.5 Build- on System of Engine In engine there are some systems which are very necessary to build an engine this is known as build-on system. There are six systems. These are Fuel System, Lubricating oil System, Cooling Water System, Starting air System, Exhaust Gas and Air Intake System, Installation Dependent Engine System Fuel System The engine is designed for continuous operation on heavy fuel oil (HFO) or light fuel oil (LFO). The design of the external fuel system may vary from one installation to another; every system will system will supply the engine with fuel at the correct temperature and pressure. It is most important that solid particles and water are properly cleaned from the fuel. The purity of fuel the fuel quality directly influences the lifetime of the injection pumps and other components in the Department of Electrical and Electronic Engineering, East West University 55

56 injection line and hence the performance of the engine. Filters and cleaning equipment are therefore very important. The internal components of fuel system are Injection pump, Injection valve (it is normally off and on when it has high pressure), Pressure Control Valve (it is very important because it safes engine from accident), Fuel Rack (is related to injection pump. It looks like a rod, which creates pumping when fuel enters. It also maintains how much fuel we will give to governor), Fuel Oil Leakage Collector (looks like tray), Camshaft (drives fuel pipe, inlet, outlet valve), Flywheel (needed for balancing power), Pulse Damper, Orifice (it is a pipe which has low diameter) 4.5.1a Fuel System on Engine The arrangement on the engine consists of a covering system, low pressure system, injectionn system with control devices. The system components are Covering System, Low Pressure System, Injection System. Figure 4.6 Fuel System on Engine.[Source: DBPAL] 4.5.1b Low Pressure System The low pressure fuel oil system on the engine consists of the fuel delivery piping and leak fuel system. The low pressure system transfer clean fuel oil to the injection pump and excess fuel oil back for reuse. The pressure of the circulating system is kept correct and constant by the pressure regulating valve mounted on the engine. The system components are Fuel delivery piping, Leak fuel system, Pressure regulating valve and Pulse damper. Department of Electrical and Electronic Engineering, East West University 56

57 4.5.1c Pressure Regulating Valve The valve is a directly controlled pressure limiting valve which is installed at the outlet of each engine to maintain the pressure of the circulating system at the correct and constant value. The components of this valve are Housing, Sliding piston, Cover, Spring guide, Spring, Protecting cap, Set screw, Nut, Sealing ring, Venting screw, O-ring. Figure 4.7: Pressure Regulating Valve. [Source: DBPAL] The sliding piston (poppet) is pressed against the sealing face by a compression spring and separates the inlet connection of the valve from outlet connection while also sealing the bore Lubricating Oil System In lubricating oil system the physical range is 0-10 bar, the current range is 4-20mA and the sensor failure limits are 3.5 ma and 20.5 ma. Here the shutdown levels are 2.0 bar 7.2 ma, 2.5 bar 8.0 ma and 3.0 bar 8.8 ma. In lubricating oil system the start blocking levels are 0.3 bar 4.5 ma, 0.5 bar 4.8 ma and 0.8 bar 5.3 ma. Start blocking is also active when sensor failure is detected and is active when it is open a Lubricating Oil System on Engine The arrangement on the engine consist of lubricating system at free end, lubricating oil system at driving end, storage system, delivery system, lubricating oil control devices and oil condition monitoring systems. Department of Electrical and Electronic Engineering, East West University 57

58 4.5.2b Lubricating Oil Delivered Lubricating oil piping is made of made of seamless carbon steel and seamless precision tubes in carbon or stainless steel. Engine block and other cast constructions contain oil channels which are used for lubrication oil delivering and collecting c Lubricating Oil flow in Piston Lubricating oil through connecting rod flows out from piston skirt, through the special nozzles to cylinder liner, forming an oil film between piston and cylinder liner surfaces. From the cylinder liner oil flows back to oil sump Figure 4.8: Lubricating Oil flow in Piston.[Source: DBPAL] The rest of the oil is used to cool the piston top with nozzles and shaker effect Cooling Water System Treated cooling water is used for cooling the cylinder lines, charge air, lubricating oil and cylinder heads including exhaust valve seats and fuel injection nozzle. The cooling water systems components are HT and LT water pump, Charge air cooler (HT and LT), Lubricating oil cooler, Thermostatic valve for HT and LT water, Non- return valve, and Shut-off valve a Cooling Water System on Engine The high temperature cooling water system cools cylinder liners and cylinder heads including exhaust valve seats and fuel injection nozzle. The systems components are HT water pump, Cylinder head, Multiduct, HT water return pipe, Charge air cooler (HT side) and Thermostatic valve for HT water. Department of Electrical and Electronic Engineering, East West University 58

59 Figure 4.9: Cooling Water System on Engine.[Source: DBPAL] 4.5.3b Cooling Water Systems on LT and HT Water Pump The engine driven LT and HT water pumps are both centrifugal pumps driven by a gear mechanism at the free end of the engine. The main components are made of cast iron and the shafts are made of acid resistant steel Starting Air System The engine is started by means of compressed air. Control air needed for timing the operation of pneumatically operated starting valves and pneumatic stop cylinders at fuel injection pumps. Starting Air System on Engine Pressurized sir is supplied to the engine through the starting air delivery piping from one side to another. The start is performed by direct injection of air into the cylinders through the starting air delivery valves in cylinder heads, which are opened by a minor part of the air volume being diverted to the correct cylinder head by the starting air distributor. Control air to the distributors is conveyed through a blocking valve, which prevents starting when the turning gear is engaged Exhaust gas and air intake system arrangement An exhaust gas system guide s wastes exhaust gases away from a controlled combustion. The exhaust gases flow through turbocharger to increase engine power. The air intake system provides the ambient air (charge sir) to engine s combustion process in combustion chamber. Department of Electrical and Electronic Engineering, East West University 59

60 The filtered air is compressed in turbocharger and cooled in the charge air cooler. The ambient air needs to be free from sea water, dust, fumes etc. The components of the system are air filter, Compressor, Charge Air Cooler (HT and LT), Cylinders, Turbine, and Waste gate valve. There are also some other components these are Exhaust outlet, cleaning water to turbine and Compressor and Charge air inlet a Exhaust gas and air intake system on Engine Exhaust gas and air intake system delivers compressed air to the combustion chamber and channels the exhaust gases out from the combustion chamber to exhaust manifold. The system can be split up into an intake section and an exhaust section b Turbocharger A turbocharger consists of an exhaust driven turbine and a compressor wheel which is mounted on the same shaft.the turbine uses the waste energy of the exhaust gases as a power source. The rotational speed of a turbocharger is normally rpm at full load depending. The basic settings of turbo-charging are Compressor, Charge Air Cooler, Turbine, Waste Gate Valve, Air Intake and Exhaust outlet. Figure 4.10: Basic settings of turbo-charging..[source: DBPAL] It converts the thermal and kinetic energy of the exhaust gases in to air pressure that can be fed in to the cylinders of an engine. The turbocharger increases specific power over naturally aspirated engine. This means a turbocharged engine can achieve more power from same engine volume. The housing fitted around the compressor and turbine collects and directs the gas flow Department of Electrical and Electronic Engineering, East West University 60

61 through the wheels as they spin. The size and shape can dictate some performance characteristics of the overall turbocharger c Water Cleaning System The cleaning water closing unit is located outside of the engine. It consists of ball valve for water closing, flow meter and connection piping. Cleaning water for turbine and compressor is led through cleaning water hose Installation Dependent Installation System This system is very important to build an engine. The component of this system are Flywheel, Flexible couplng, Common base frame, Resilient mounting and Engine identification signs a Flywheel The flywheel as a rotating element is encased with a protective cover preventing physical injuries. Figure 4.11: Flywheel.[Source: DBPAL] The flywheel is connected to the crankshaft with fitting screws and normal screws. The amount of fitting screws is dependnt on the engine configuration b Flexible couplng The power tranasmission from the engine is accomplished through a flexible coupling mounted on the flywheel. The crankshaft with an additional sheild bearing at the driving end. Therefore a rather heavy coupling can be mounted on the flywheel without using intermediate bearings. Department of Electrical and Electronic Engineering, East West University 61

62 4.5.6c Common base frame The engine and the alternator are rigidly mounted on the common base frame, the alternator aligned with fitting pieces. 4.6 Engine Control System A control unit in general is a central (or sometimes distributed but clearly distinguishable) part of the machinery that controls its operation, provided that a piece of machinery is complex and organized enough to contain any such unit. One domain in which the term is specifically used is the area of computer design. In the automotive industry, the control unit helps maintain various functions of the vehicle. In engine there is a control system which is divided into three parts, these are MCM (Main Control Module) ESM (Engine Safety Module) PDM (Power Distribution Module) MCM (Main Control Module) In MCM, engine controls the speed and load. The output will go to the actuator (generator). Here the current range will be (20-160mA), when 20mA is used the engine will stop and works at offload; but when 160mA is used the engine will work at full load. At DBPAL (Dutch Bangla Power Plant and Associates Ltd) the current range is 95mA. MCM shutdown input intended for the engine s main controller. It is possible to configure for single or dual wire operation. single wire operation dual wire operation ESM (Engine Safety Module) It is need for an independent stand-alone safety system, to replace old, outdated systems, for Department of Electrical and Electronic Engineering, East West University 62

63 standardised unified marine and power plant solutions, for a compact, certified and classified solution, for specific I/O s and functions not available in other systems. Main Tasks The main task of ESM is to provide safety for the engine. It helps to standardised stop circuitry for all applications, predefined settings, standard interface to engine control system and external systems. It is also used for speed measuring and related functions. 4.7 Maintenances and safety For engine, maintenance and safety is very important for an engine. Without maintenance and safety engine become in danger and it will lose its better life Maintenances In DBPAL (Dutch Bangla Power and Associates Ltd), use HFO for running the plant. So we have to give special care at fuel quality. Also with fuel, we have other duties for maintenance purpose.these is given below:- Check tightening of the connecting rod screw We have to check tightening of the connecting rod screw after the first 50 operating hours on a new engine and, after overhaul those screws that had been opened. Check tightening of the counterweight fastening nuts We have to check tightening of the counterweight fastening nuts after the first 50 operating hours on a new engine. Check oil level in governor We have to check oil level, and look for leaks Check pressure drops The cartridges are to be replaced when the pressure difference indicator shows too high pressure drop. Department of Electrical and Electronic Engineering, East West University 63

64 Check oil level in sump oil/tank We have to check oil level by means of dip stick. It is very important for an engine. Without checking oil level in sump oil the engine may be in danger. Check tightening of injection pipe connections We have to check the tightening of injection pipe connections on a hot engine after the first after 50 operation hours on a new engine and, after overhaul, those connections which have been opened. Also we have to check the tightening of the nuts. Above these, we also have the duty to check the cooling system, cylinder, LT and HT side, crankshaft, bearing of the engine Safety purpose All diesel engines have some basic safety. This basic safety protects the engine from danger. The basic safety of a diesel engine is given below: Lube oil low pressure shut down High temperature shut down Over speed shut down 4.7.2a Lube oil low pressure shut down Lube oil low pressure shut down is the basic safety of a diesel engine. Lube oil is needed for engine as we need blood in our body. The pressure exist here is 6 bar (normal engine).when pressure decreases and comes to 3 bar then it gives ESM alarm. But when pressure decreases and comes to 2.5 bar the engine will stop automatically b High temperature shut down High temperature shut down is another basic safety for a diesel engine. The normal temperature of a diesel engine is 96 0 C. If the temperature of the engine increases by any reason then the engine will give alarm at C. The engine will stop when the engine goes to C. Department of Electrical and Electronic Engineering, East West University 64

65 4.7.2c Over speed shut down This safety is very important for an engine. Normally the engine runs at 750 rpm. There are two over speed shut down speed these are 847 rpm(113%) and (117 %).When the speed of the engine increases from normal speed, the engine will be shut down. There is also three redundant speed sensor inputs which have its own power supply, over speed trip circuit. Department of Electrical and Electronic Engineering, East West University 65

66 5. GENERATOR 5.1 Introduction In the generator section in DBPAL we have spent 5 days, from 31 st December 2011 to 4 th January In this section we have come to know from DBPAL about the construction of generator, operation principle of generator, design and dimensioning, different types of protection synchronization, grounding, NGR, maintenance of generator etc. An electrical generator is a device that produces electrical energy from mechanical energy source. The process is known as electricity generation. In principle AC generator can be called alternator. We get reactive power from generator. Generators are installed on common base frame for easy and reliable installation and first alignment. Flexible coupling are used to minimize torsional vibration and to increase power quality. 5.2 Construction of Generator Generator is constructed by the following important parameters which are given below a Stator The stator of an AC generator is the part which is stationary. Here, stator core is made of highgrade, low-loss silicon steel sheets. Sheet thickness is 0.5 mm (insulated on both sides). Frame and end shields are made of fabricated steel. Stator frame end parts and the middle part with the core are welded together. Bearing housings are bolted to the end shields. Figure 5.1: Stator (left) and Rotor (right).[source: DBPAL] Department of Electrical and Electronic Engineering, East West University 66

67 5.2.1b Rotor The rotor of an AC generator is the rotating component of the generators. Rotor is designed to withstand the vibration caused by the prime mover and stresses appearing up to 120 % of rated speed and critical rotational speed is at least 1.5 times of the nominal speed. Here, shaft is made of forged steel and poles are constructed of punched and stacked steel plates, which are provided by damper winding. Aluminum is used for cooling and supporting of windings c Windings and Insulation Both stator and rotor windings withstand the influence of humidity, moisture and chemically aggressive substances. All windings are vacuum-pressure impregnated (VPI). Winding insulation exceeds Class F requirements (temperature limit 155 C).Here in DBPAL(Dutch Bangla Power and Associates Ltd.) uses class F. Mainly windings are made of from wound copper coils but rotor winding are made of insulated enameled rectangular copper as a multilayer winding. Here support rings on the winding ends are impregnated together with the winding. Figure 5.2: Parts of Generator. [Source: DBPAL] 5.3 Operation Principle of Synchronous Generator Synchronous generator is a rotating machine whose speed of rotation is fixed to the ratio of the supply frequency and the number of pole pairs. n = 120 x f / p speed (rpm) f =frequency (Hz) p= number of pole pairs Department of Electrical and Electronic Engineering, East West University 67

68 5.3.1 Working Principle From faraday s law of induction we know, the induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit. If, Φ = Magnetic flux, N = Number of turns in the coil, t = Time and ε = Induced electromotive force (EMF). Then from the faraday s law we get, ǫ= N Figure 5.3: Faraday s Law of Induction.[Source: DBPAL] From the figure we can see that a coil of N turns is rotating inside a magnetic field. The magnetic flux varies with time, thereby inducing an EMF Direction of Rotation The direction of rotation is indicated on the generator rating plate. The generator ends are designed D (drive-end) and N (non- drive-end).the generator rotates counter-clockwise, when viewed from the D-end to N-end Synchronous Generation on different loading condition Synchronous generator works at different loading conditions, as like as no-load and reactive load a No- Load Rotating, magnetized rotor pole will create magnetic flux through conductors of stator coil. Voltage will be induced to each conductor of the coil multiplied by the number of effective turns, Department of Electrical and Electronic Engineering, East West University 68

69 the number of coil sides within a coil group and also the number of series connected coil groups, a rated voltage will be generated in the generator terminals b Reactive-Load The current being at 90 phase angle (angle between voltage and current) with the voltage will create magnetic flux in the same axis as field current (No active power is needed to rotate generator except losses of the generator). Inductive load Phase angle +90 (current behind the voltage). Capacitive load Phase angle -90 (current ahead the voltage). Inductive current creates flux affecting opposite direction to flux created by field winding in order to prevent voltage decreasing, field current shall be increased Capacitive current creates flux affecting same direction to flux created by field winding in order to prevent voltage rising, field current shall be decreased Synchronous Generation on different Operation Mode There are mainly three types of operation modes in synchronous generator. Such as Solo Mode Island Parallel Mode Grid Parallel Mode 5.3.4a Solo Mode Only one generator is running independently. Voltage and frequency can be control here b Island Parallel Mode More than one generator sharing common load and not parallel with grid. In case of Island mode active and reactive power supplied to the bus bar depends on load. Frequency and voltage of the busbar we are able to control. On ships and power plants which are isolated from other systems, island parallel mode is used. Department of Electrical and Electronic Engineering, East West University 69

70 Table 5-1: Modes of Operation Control Options Solo Island Parallel Grid Parallel DG Load No Yes Yes Total Plant Load No No Yes Voltage Yes Yes No Frequency Yes Yes No 5.3.4c Grid Parallel Mode or Utility Mode One or more generator is parallel with grid. We are able to control active and reactive power supply to the grid. Frequency and voltage depends on grid, so we cannot control these Different Control Mode There are many types of control modes in synchronous generator. In DBPAL, they are mainly uses the following control modes for synchronous generator. Voltage control mode Power factor control mode DG (diesel generator) load system control mode Speed droop and True kw control Isochronous speed control Digital control 5.3.5a Voltage Control Mode Voltage control without droop can be used for single generator when generator shall only maintain the terminal voltage at pre-set value. Voltage droop control is a universal, flexible control method, which can be used in single unit operation, in parallel operation with other units in an island system or in parallel operation with the rigid utility - due to voltage droop, the line voltage drops with increasing reactive power. Voltage droop is the reduction in voltage from no load voltage to full load voltage. It is expressed as percentage of rated voltage. % Droop = [(No Load Value Full Load Value) X 100/Rated Value]. Voltage Droop setting in Generator is normally 5%. Department of Electrical and Electronic Engineering, East West University 70

71 Figure 5.4: Voltage Control Mode.[Source: DBPAL] 5.3.5b Power factor control mode Power factor control mode is possible only when a generator is connected to a larger power system, where other synchronous machines (big majority of output) determine voltage and can absorb reactive power. Note that before synchronizing to the network, the generator must always operate in voltage control mode. Power factor control keeps the angle Φ constant regardless of the output active power, P. Figure 5.5: Power Factor Control Mode.[Source: DBPAL] S² = P² + Q², where S = Apparent Power, kva P = Active Power, kw Q = Reactive Power, kvar cos φ = P/S Active power (P) is generated by the prime mover which leads us to the conclusion that it has to be controlled by the prime mover. Reactive power (Q) is really generated by the generator in accordance of load and excitation. (Excitation being the way of adjusts the generator.) Department of Electrical and Electronic Engineering, East West University 71

72 5.3.5c DG (diesel generator) load system control mode DG (diesel generator) load system control mode works in two ways. These are Auto Here engine control by active power (P) and generator control by power factor. PLC (programmable logic controller) takes care via prime controllers. Figure 5.5: Auto (left) and Manual (right). [Source: DBPAL] Manual Here, engine control either SPEED DROOP or kw control mode. Active load reference is changed by S4- button. Generator can be controlled either VOLTAGE DROOP or Power Factor control mode. Reactive load reference is changed by S5- button d Speed Droop and True kw Control In DBPAL speed drop and true KW control is very important for generators which are discuss below- Speed Droop Control Speed droop is the reduction in speed from no load speed to full load speed. It is expressed as percentage of rated speed. % Droop = [(No Load Value Full Load Value) X 100/Rated Value]. Speed Droop setting in Generator is normally 4%. Department of Electrical and Electronic Engineering, East West University 72

73 Figure5.6: Speed droop control (left) & True kw control (right).[source: DBPAL] True kw Control It is parallel with grid. Here breaker is closed and kw control is selected. In true kw control speed bump less change over to droop control. 5.4 Design and Dimensioning It is very important for generator without knowing designs issue we can t the operation criteria of a generator Automatic Voltage Regulator (AVR) The main purpose of AVR are to control terminal voltage with suitable accuracy, to keep machine within permissible operating range, to ensure stable operation with network or the machines, contribute to transient stability subsequent to a fault. Figure 5.7: Schematic diagram of AVR.[Source: DBPAL] Department of Electrical and Electronic Engineering, East West University 73

74 5.4.2 Synchroscope Synchroscope is an instrument used for indicating whether two alternating-current (ac) generators or other ac voltage sources are synchronized in time phase with each other. Its main use is in power supply networks where, if two generators are to be operated in parallel or an additional generator is to be coupled into the grid, it is essential that the generator voltages should be matched in amplitude, frequency, and phase Design Issue Figure 5.8: Synchroscope. [Source: DBPAL] Designing is very necessary for a generator. Without proper designing one generator can lose its better life a Power The Generator has to be dimensioned so, that it is able to produce the required apparent power without warming too much b Frequency & Speed With equal power, the slower the speed, the bigger generator is needed. In other words, the needed Torque defines the size. Speed affects also to the mechanical design of the rotor c Voltage level Voltage level defines the insulation class of the winding as well as air insulation distances. Department of Electrical and Electronic Engineering, East West University 74

75 5.4.3d Temperature rise Temperature rise is maximum allowed winding temperature above ambient temperature at rated load. Temperature rises are based on ambient temperature 40 C. Pre-designed generators meet temperature rise class F e Cooling method: There are two cooling systems, direct air cooling and water cooling. For direct air cooling, the generator is cooled with a shaft mounted fan. The cooling air is drawn in through air filters and blown out to the environment on standard arrangement. For water cooling, the temperature of cooling air typically higher with equal ambient temperature. 5.5 Synchronization When two or more electrical generating sets or systems are paralleled to the same power distribution system, the power sources must be synchronized properly. Without proper synchronization of the oncoming unit or system, power surges, mechanical and electrical stress will result when the tie or generator breaker is closed. Figure 5.9: Meters for synchronization.[source: DBPAL] Condition for Synchronization For synchronize a generator, we have to look at four condition. They are Phase Sequence Frequency and Voltage Phase angle Department of Electrical and Electronic Engineering, East West University 75

76 5.5.1a Phase Sequence During installation phase seq. has to be checked with high voltage sticks. In this case for synchronization we have to very careful about generator rotation direction. Figure 5.10: Phase Sequence.[Source: DBPAL] 5.5.1b Frequency and Voltage Here frequency and voltage has to be match with the grid. The grid frequency in Bangladesh is 60Hz. To adjust frequency we have to increase or decrease speed. Figure 5.11: Synchronization of frequency.[source: DBPAL] 5.5.1c Phase Angle Phase angle has to be match with the grid. To adjust phase angle it needs frequency fine tuning and speed settlement. Department of Electrical and Electronic Engineering, East West University 76

77 5.5.2 Worst Case Under the worst conditions, the voltages between the two systems can be twice the peak operating voltage of one of the systems, or one system can place a dead short on the other. Figure 5.12: Worst Case.[Source: DBPAL] Extremely high currents can result from this which put stress on both systems. 5.6 NGR (Neutral Grounding Resistor) The purpose of a neutral grounding resistor is to limit the ground fault current to a safe level so that all the electrical equipment in the power system is protected. The resistor should be the only current path between the neutral of power transformers or power generators and ground. When the neutral of a system is not grounded it is possible for destructive transient over voltages to appear from line to ground during normal switching of a circuit having a line to-ground fault. Experience has proved that these over voltages cause aging and failure of insulation at locations on the system other than at the point of fault. In this way, a relatively unimportant line-to ground fault on one circuit may result in considerable damage to equipment and interruption of service on other circuits, not to mention the increased difficulty in finding the original location of the problem. A neutral grounding resistor is designed to limit the ground fault current to a safe value while at the same time letting enough current to flow to operate the protective relays that will clear the fault. Department of Electrical and Electronic Engineering, East West University 77

78 Figure 5.13: NGR. [Source: [8]] Advantages of using a neutral grounding resistors are reduced operation and maintenance expenses, fast isolation of the original fault, reduced transient over voltages, reduced physical damage on the equipment at fault, simplification of ground fault location, increased life and protection of transformers, generators and related equipment, reduced frequency of faults, improved service reliability, increased protection in the use of lightning arresters, and increased safety. 5.7 Grounding Ground or earth is the reference point in an electrical circuit from which other voltages are measured, or is a common return path for electric current, or a direct physical connection to the Earth. Electrical circuits may be connected to ground (earth) for several reasons. In mains powered equipment, exposed metal parts are connected to ground to prevent contact with a dangerous voltage if electrical insulation fails. Connections to ground limit the build-up of static electricity when handling flammable products or when repairing electronic devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor. Department of Electrical and Electronic Engineering, East West University 78

79 5.7.1 The Objective of Grounding Grounding can minimize the damage for internal ground faults. It can limit mechanical stress in the generator for external ground faults. And also limit temporary and transient over-voltages on generator insulation. It provides means of generator system ground fault detection. It coordinating the protection of the generator with the requirements of other equipment connected at generator level Classification of Grounding The grounding can be divided into the following three areas with respect to purpose: Neutral Point Ground Safety Ground Equipment Ground 5.7.2a Neutral Point Ground The purpose is to establish the ground reference of the system. The neutral ground connection is usually made to the neutral of equipment like generators and transformers. Figure 5.14: Grounding.[Source: DBPAL] 5.7.2b Safety Ground This is made for protecting personnel from injury and property from damage. These connections are made to parts of the system that are usually not energized but may become under abnormal or fault situations. Department of Electrical and Electronic Engineering, East West University 79

80 5.7.2c Equipment Ground Grounding made to ensure a low impedance return path for ground current should be electrical faults occurs. Between live conductors and equipment enclosure, in order to secure that a trip of the faulty circuit is made in a short time. 5.8 Generator Maintenance For generator maintenance some essential activity has to be taken. These are Check air filter cleanliness Pressure & flow / level of bearing lubrication Rotating diodes & surge suppressor inspection IR (Insulation Resistance) Value measurement PI (Polarization Index) measurement NGR value measurement IR (Insulation Resistance) The insulation resistance value informs about wetness of windings and degree of contamination in the insulation. Acceptable limit of IR value is R 40ºC = 1 + U Where, R 40ºC = Corresponding IR value of winding at 40ºC in MΩ U = Machine voltage in kv 5.8.1a Effect of ambient temperature IR value decreases due to the temperature rise and measurement standard temperature is 40ºC b Effects of dirt & humidity IR value is inversely proportional to dirt & humidity. Hence IR decreases with the increase of dirt & humidity. Department of Electrical and Electronic Engineering, East West University 80

81 5.8.2 PI (Polarization Index) The PI usually ranges between 1.0 and 4.0. When the windings are humid and dirty, the PI is approx 1.0. As a thumb rule the following minimum values may be applied, for class A insulation machine 1.5 and for class B to F insulation machines 2.5. The Polarization Index is given by the relation: PI = R1min/ R15s or R10min/ R1min Where, R1min = IR value measured for 1 minute R15s = IR value measured for 15 seconds R10min = IR value measured for 10 minutes 5.8.2a Effect of ambient temperature PI is less dependent on the temperature than IR value. It is considered independent of temperature below 50ºC. High temperature can cause unpredictable change in PI. PI should not be checked at ambient above 50ºC b Effects of dirt & humidity PI is inversely proportional to dirt & humidity. Hence PI decreases with the increase of dirt & humidity. 5.9 Generator Protection Protection of generator is the most complex and elaborate. The reason being the following: Generator is a large machine and is connected to bus bars. It is accompanied by unittransformers, auxiliary transformer and bus system. It is accompanied by excitation system, prime mover, voltage regulator, cooling system etc. hence it is not single equipment. The protection of generator should be co-ordinate with associated equipment. It is costly and important equipment. It should not be shut off as far possible because that would result in power shortage and emergency. There are many types of protection for generator. These are: Differential Protection, Over & Under Voltage Protection, Over & Under Frequency Protection, Over Current Protection, Department of Electrical and Electronic Engineering, East West University 81

82 Thermal Overload Protection, Under Reactance or Loss of Excitation Protection, Reverse Power Protection, Restrained Over Current Protection, and Earth Fault Protection Differential Protection Differential protection is essentially a unit protection and protection zone is determined by location of CT s. This type of protection is applicable for generators, transformers, motors, transmission line, and bus zone. Differential relay current is proportional to vector difference between the currents entering and leaving the protected zone. Figure 5.16: Operation criteria of differential protection.[source: DBPAL] In Normal condition, Id =I1 - I2 = 0; (Relay do not operate) During Internal fault Id =I1 - I2 = not zero; (Relay operates) During External fault Id =I1 - I2 = 0; (Relay do not operate) Fault currents are same in both CT s. Many types of problems arise in differential protection. Such as: Difference in Pilot Wire Lengths, Difference in CT Ratio errors during short circuit, Saturation of CT during short circuit, Changing of Taps in transformers as it alters the voltage/current ratio, Magnetizing Inrush Current in transformer while switching in. To overcome the above difficulty, biased differential relay, VAMP 210 and VAMP 265 is used to detect electrical faults in a power network and to give open signals to a circuit breaker in case of fault. Department of Electrical and Electronic Engineering, East West University 82

83 Figure 5.15: VAMP 210 (left) and Biased Differential Relay (right).[source: DBPAL] Biased Differential Relay The biased differential relay has an additional restraining coil. Here, operating coil is connected to the midpoint of the restraining coil. The Restraining current increases in proportional to the operating current thereby preventing the relay from mal operation. VAMP 210 The VAMP 210 needs to know the local line frequency to be able to take 32 samples/cycle. If there is no line-to-line voltages connected to the relay, the relay will use the default frequency to get 32 samples/cycle. The local frequency is automatically saved as default frequency in a non-volatile memory. This type of protection relay can measured two types of value such as directly measured values (Phase currents, Residual currents, Line-to-line voltages, Zero sequence voltage, Frequency) and calculated values (Phase-to-ground voltages, Apparent power S, Active power P, Reactive power Q, Power factor) Over & Under Voltage Protection Over and under voltage protection is very important protection for generator which we studied during our internship program in DBPAL a Over Voltage Protection Over voltage protection has taken to protect against over voltage. It is applicable for generators, transformers, and motors. Over voltage protection is needed when there are sudden load shedding, fault in Automatic Voltage Regulator (AVR), leading power factor, and due to grid voltage. If we don t take over voltage protection there might be insulation failure. Department of Electrical and Electronic Engineering, East West University 83

84 There are two stages of protection. Low set stage 15 % x Vn (Vn=nominal voltage) kv Time delay: 1-2 sec High Set stage % x Vn kv Time delay: Instantaneous 5.9.2b Under Voltage Protection Under voltage protection has taken to protect against under voltage. It is applicable for generators, transformers, motors, and A.C networks. Under voltage protection is needed when there are sudden load shedding, fault in Automatic Voltage Regulator (AVR), very lagging power factor, and due to grid voltage. If there is no use of under voltage protection the load current will be increase. There are two stages of protection. Low set stage I 80 % x Vn (Vn=nominal voltage) 8.8 kv Time delay: 20 sec Low Set stage II 65 % x Vn 7.15 kv Time delay: 0.06 sec Over & Under Frequency Protection Over and under frequency protection is very important protection for generator which we studied during our internship program in DBPAL. Department of Electrical and Electronic Engineering, East West University 84

85 5.9.3a Over Frequency Protection Over frequency protection has taken to protect against over frequency. It is applicable for generators, and prime-mover. Over frequency protection has to be set 52.5Hz, 4 sec time delay. Over frequency protection is needed when there is sudden load rejection, fault in speed regulating system, fault in the fuel system, and due to grid frequency. If we don t take over frequency protection it can causes over heat to the rotor and field windings which may lead to failure and core gets saturated as V/f ratio is not maintained during fluctuation b Under Frequency Protection Under frequency protection has taken to protect against under frequency. It is applicable for generators, and prime-mover. Under frequency protection has to be set 47.5Hz, 4 sec time delay. Under frequency protection is needed when there is sudden over load, fault in speed regulating system, and fault in the fuel system. If we don t take under frequency protection it can causes over heat to the rotor and field windings which may lead to failure and there may be present of insufficient cooling air Over Current Protection Over current protection has taken to protect the equipment from overloading and short circuit. It also acts as backup protection for differential protection relay. It is applicable for the generators, transformers, motors, transmission line, and bus zone. If we don t take over current protection it can causes short circuit and earth fault, and there may be over load in the generator. There are two stages of protection. Low set stage (Rough Over load protection) The low set stage of the over current unit can be configured for inverse time characteristics, IDMT (Inverse Definite Minimum Time) characteristics. Here it is 1.2 times bigger than nominal current, 1.2 x In (In=nominal current). There are also four set of characteristics curves like normal inverse (NI), very inverse (VI), extremely inverse (EI) and long time inverse (LTI). High set stage (Short circuit protection) 2.5 x In Time delay: Instantaneous Department of Electrical and Electronic Engineering, East West University 85

86 5.9.5 Thermal Overload Protection Thermal overload protection has taken to protect from high temperature due to continuous overload. Monitoring site is done by thermal replica of the machine, a thermal relay. It is applicable for the generators, transformers, and motors. If there is no use of thermal overload protection then winding insulation can damage at excessive temperature and shortens the service life of generator. The thermal stage calculates the temperature rise using rms values of the measured phase currents. The calculation is active all the time unlike inverse time over current stages, which do calculate the delay only when the current exceeds a pick-up value and forgets all history when current falls below the pick-up value. Thermal over load relays permit overload of generators up to 110% as allowed by the manufacturers with specific time constant. Generally generators are manufactured to withstand 110% overload for one hour Loss of Excitation Protection Loss of excitation protection has taken to protect the generator from loss of field excitation and under excitation. It detects the loss of excitation by measuring the reverse KVAR drawn by the generator which is similar to reverse power relay. Loss of excitation protection has to be set Leading. It is needed when we open a field switch or field circuit breaker. If we don t take loss of excitation protection it can causes loss of terminal voltage and synchronism, draws reactive power from bus bars and runs as induction generator, reduced power output, stator currents increase above normal rated current, overheating of rotor and generator winding Earth Fault Protection Earth fault protection has taken to protect the equipment from earth fault. It is applicable for the generators, transformers, motors, transmission line, and bus bar etc. If we don t take this protection, it may be increases by 3 times of phase to earth voltage, unstable/floating neutral, unsafe for personnel working on equipment. For directional earth fault protection VAMP 210 is used in DBPAL. Various methods of earth fault protections are available for different scheme of earthing. These are given below: Department of Electrical and Electronic Engineering, East West University 86

87 Neutral Over Current Neutral over current is a simple non selective earth fault protection which acts for external faults. It is used in solidly earthed systems as a backup protection. Figure 5.16: Neutral Over Current Protection. [Source: DBPAL] Residual Over voltage It is used in high resistance earthing system and here relay acts after a threshold of residual voltage. Directional Earth fault Relay It is used for 100% protection of winding against phase to earth faults Backup or Standby Generator A standby generator is a back-up electrical system that operates automatically. Within seconds of a utility outage an automatic transfer switch senses the power loss, commands the generator to start and then transfers the electrical load to the generator. The standby generator begins supplying power to the circuits. After utility power returns, the automatic transfer switch transfers the electrical load back to the utility and signals the standby generator to shut off. It then returns to standby mode where it awaits the next outage. To ensure a proper response to an outage, a standby generator runs weekly self-tests. Department of Electrical and Electronic Engineering, East West University 87

88 6 PROBLEMS & RECOMMENDATION 6.1 Problems During our internship program we have faced some problems. Such as. Because of the company confidentiality, we were not able to see the internal circuit designs of the equipment which we felt necessary for us to see. We faced some problems during internship as we had not completed two courses namely (Power Stations and Power Electronics) which were related to the internship program. 6.2 Recommendation After finished internship we want to recommend something which is given below. Students should complete the courses related to their internship before beginning the program. Taking the courses before the internship helps the students understand the topic much better. The tenure of the internship program with DBPAL was only for two weeks. Even these short duration gave us exposure to the practical aspects of theoretical issues. We believe longer internship program would benefit us better. Department of Electrical and Electronic Engineering, East West University 88

89 7. CONCLUSION We spent some remarkable days at DBPAL during our internship program. DBPAL could be regarded as the practical ground of the Electrical and Electronic Engineering Department of East West University. The theories that we have learned at the University could be observed at the DBPAL. We consider ourselves very much lucky to have our internship program with a reputed power station company like DBPAL. It gave us an opportunity to apply our theoretical knowledge in practice. Our achievements from DBPAL are: Industrial training provided by DBPAL has enriched our practical knowledge. It has opened our eyes about practical operation of different equipments. The authorities in DBPAL were very concerned about all kinds of safety. The friendly environment in DBPAL encouraged us to co-operate with each other. We have learned a lot and obtained practical knowledge from our internship at DBPAL, which will help us in our future life. Department of Electrical and Electronic Engineering, East West University 89

90 REFERENCE [1]. ent/lightning_arresters.html [2]. [3]. [4]. [5]. Circuit-Breaker.html [6]. Circuit-Breaker.html [7]. [8]. Switchgear & Protective Relays by Sunil.S.Rao [9]. V.K. Mehta & Pohit Mehta, Principles of Power system, 4 th Revised Edition, 2009, S.Chand & Company Ltd, [10]. V.P. Vasandani & D.S.Kumar, Heat Engineering, 4 th Revised Edition, 1995, Metropolitoan Book Co. Pvt. Ltd. [11]. [12]. Department of Electrical and Electronic Engineering, East West University 90

91 Department of Electrical and Electronic Engineering, East West University 91

92 Department of Electrical and Electronic Engineering, East West University 92

93 Department of Electrical and Electronic Engineering, East West University 93

94 Department of Electrical and Electronic Engineering, East West University 94

95 Department of Electrical and Electronic Engineering, East West University 95

96 Department of Electrical and Electronic Engineering, East West University 96

97 Department of Electrical and Electronic Engineering, East West University 97

98 Department of Electrical and Electronic Engineering, East West University 98

99 Department of Electrical and Electronic Engineering, East West University 99

100 Department of Electrical and Electronic Engineering, East West University 100

101 Department of Electrical and Electronic Engineering, East West University 101

102 Department of Electrical and Electronic Engineering, East West University 102

103 Department of Electrical and Electronic Engineering, East West University 103