SWITCHGEAR AND PROTECTION (SGP) (403147) SHREE RAMCHANDRA EDUCATION SOCIETY S SHREE RAMCHANDRA COLLEGE OF ENGINEERING, LONIKAND, PUNE

Transcription

1 SHREE RAMCHANDRA EDUCATION SOCIETY S SHREE RAMCHANDRA COLLEGE OF ENGINEERING, LONIKAND, PUNE DEPARTMENT OF ELECTRICAL ENGINEERING LAB MANUAL SWITCHGEAR AND PROTECTION (403147) BE (EE) Semester-VIII S.R.C.O.E, PUNE Page 1

2 INDEX Sr. No. Name of Experiment Page No. 1. Study of switchgear testing kit Study of Fuse, MCB & their testing Study and testing of contactors Study and testing of thermal overload relay for Induction Motor protection 5. Study and plotting Characteristics of IDMT type Induction over current relay Percentage differential protection of transformer Protection of alternator Study of various LT switchgears like RCCB, timers S.R.C.O.E, PUNE Page 2

3 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY OF SWITCHGEAR TESTING KIT LABORATORY MANUAL EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/01 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:03-07 STUDY OF SWITCHGEAR TESTING KIT AIM: To study the switchgear testing kit. APPRATUS (Specifications): Sr. No. Variable AC current: Name of Equipment Range 0-50 Amp. with 500 VA/1000VA Variable AC voltage: V AC, 2 Amps. Variable DC voltage: V DC, 2 Amps. Mains Input:(three terminal instrument Normal 230V AC, 50 Hz, mains plugs provided.) Outputs: Variable AC current source: 0-20A. VA burden maximum: 200VA. Timer OFF connection from relay contacts. Monitors: Other components: Time counter: Range: milli seconds with auto range. Accuracy: +/- 0.05%. Mains ON/OFF switch, Indication Lamps, Sturdy Current variable knob. DESCRIPTION: This unit is specially designed to suit relay testing requirements of power station testingengineers. Purpose of modern instrumentation engineering is to reduce the total instrumentweight and still give single equipment which can be used for testing of different type ofpower system relays. The unit is a portable. Stability and accuracy of digitalindication is in-built. Numbers of functional units are included in single cabinet. They can beused S.R.C.O.E, PUNE Page 3

4 individual or in association with other unit. The connection terminals are front loadedand plug in or wire connections can be used. The set operates on single phase 230 Volts, AC, 50 Hz power supply and provides acontrollable test voltage and completely adjustable output current. The unit is housed in apowder coated sheet metal panel with table mounting facility, detachable lid, latches andcarrying handles. All the switches, terminals, meters and knobs are mounted on frontof the panel, with properlabels. Terminals for the test voltage, current source and relay contact terminals are provided on the front Ammeter and digital time interval meter is also provided on thefront of the panel for metering purpose. The ammeter will indicate in the percentage of therange selected and the voltmeter will indicate the voltage. Mains ON indication is provided. The voltage circuit and current circuit can be used simultaneously. FEATURES: Micro controlled based time measuring unit with 1 ms resolution. Special provision for relay s ON delay/off delay time measurement. Specially designed for testing of all types of IDMT over current relay/under-over voltage relay/auxiliary relay. Designed for checking the operating characteristic of protective relay on site. With timer control circuit, timer automatically starts output is initiated and stops when the. Auto cut-off facility. Provided with Single pole IDMT Over Current/ Earth fault relay. Numerical/ Electromechanical type of Relay with Secondary CT ratio 1A/ 5A. PROCEDURE TO USE CURRENT SOURCE: 1. Connect the relay coil to current range selector. 2. Switch on Mains. 3. Select current range from current selector switch 4. To adjust current range for the injection, keep the timer open, marked as +V & C2. 5. Push the stat button, after staring, the timer gets started & current to be injected should be as per indication on the ammeter as % of the selected range. 6. After setting the current range, short the time terminals, to automatically stop the current source. 7. Now connect the NO contactor the relay to the timer terminals are marked as +V & C2. 8. Reset the timer & reset the current circuit by pushing the start button& current will be injected & relay will be operated. The NO contacts turn NC & the timer circuit gets automatically cut off. 9. After testing of the relay for 2 to 3 times at various ranges, zero the current control knob. 10. Switch OFF the main supply. S.R.C.O.E, PUNE Page 4

5 PROCEDURE TO USE VOLTAGE SOURCE: 1. Switch ON main switch. 2. Select AC/DC voltage source as per requirement by switching selector switch to 1 or 2 Position for AC /DC source respectively. 3. The voltage can be adjusted from the voltage control knob as per requirements. 4. After using for various operations turn OFF the voltage selector switch. 5. Turn OFF main switch & before zero voltage control knob is zero. 6. Voltage is shown on the voltmeter on the respective meters for Ac & DC. Procedure for Time Vs Current (IDMT)Characteristics test 1) Connect the relay coil (termination ) to the current source (Terminated as ). as shown in the figure 1. 2) Connect the Aux. contact of the relay ( ) to the Timer contact of the kit ( ). 3) Connect the 230V AC supply to the kit 4) Keep the TMS setting at maximum position (1 sec). 5) Keep the Phase setting plug at 2.5A (50%) Setting 6) Switch ON the unit and push the Start Push button. 7) Now slowly increase the current value upto 3A by adjusting the current variable knob. 8) Switch OFF the output by pushing the stop PB and reset the Timer without changing the setting 9) Switch ON the output, which will also start timer. Timer will stop counting when the relay trips Note the delay. 10) Repeat the procedure for various current values as per table no ) Switch OFF the mains supply. Procedure for Testing TMS Setting 1) Connect the relay coil (termination ) to the current source (Terminated as ). as shown in the figure 1. 2) Connect the Aux. contact of the relay ( ) to the Timer contact of the kit ( ). 3) Connect the 230V AC supply to the kit. 4) Keep the TMS setting at minimum position (0.1s). 5) Keep the Phase setting plug at 2.5A (50%) Setting. 6) Switch ON the unit and push the Start Push button. 7) Now slowly increase the current value up to 3.5A by adjusting the current variable knob. 8) Switch OFF the output by pushing the stop PB and reset the Timer without changing the setting. 9) Switch ON the output, which will also start timer. Timer will stop counting when the relay trips Note the delay. 9) Repeat the procedure for various TMS setting values as per table no ) Switch OFF the mains supply. S.R.C.O.E, PUNE Page 5

6 OBSERVATION TABLE Table No. 1.1 Pick up Test TMS(Time Multiplier setting) Setting- 1 Sec. Sr.No. % Set (I >) Current (Amps) A (50%) A (75%) 3. 5A (100%) A (125%) A (150%) A (175%) 7. 10A (200%) Table no. 1.2: Time Vs. Current (IDMT) Characteristics for O/C or EF TMS Setting: 1 Sec. Phase trip setting as 2.5A (50%) Set current at 3A 5A 7.5A 10A 3A Time in Sec. Phase trip setting as 3.75A (50%) Set current at 5A 7.5A 10A 15A Time in Sec. Phase trip setting as 5A (100%) Set current at 7.5A 10A 15A 20A Time in Sec. Table no. 1.3: TMS Setting Test: S.R.C.O.E, PUNE Page 6

7 Current to be injected : 3.5 A SWITCHGEAR AND PROTECTION (SGP) (403147) TMS Switch Position Phase Switch At 2.5 A X 0.1 X 0.2 X 0.5 X 0.75 X 0.1 CONCLUSION: In this way we studied the switchgears testing kit. S.R.C.O.E, PUNE Page 7

8 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY OF FUSE & MCB & TESTING OF MCB EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/02(A) SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING PAGE:08- SEMESTER : II (BE) 10 STUDY OF FUSE & MCB & TESTING OF MCB AIM: Study of Fuses THEORY: The fuse is a protecting device of simplest form. It consists of a small piece of metal when excessive current flows through it. The metal elements melts & the current is interrupted & the circuit gets disconnected from the supply.thus it protects the circuit from dangerous excessive current. So fuse is used to interrupts a fault current.it is simple protective device which works on the principal of current interruption, if current through it becomes excessive. Types of fuse 1. Expulsion fuses 2. Cartridge fuse 3. Drop out fuse 4. Liquid fuse 5. Open fuse 6. Striker fuse 7. Switch Fuse 8. HRC Fuse 1. Expulsion Fuse - The Expulsion fuse consists of modern cutout. In such fuse the arc occurring during the current interruption is extinguished by the expansion produced by the arc. 2. Rewirable Fuse or Semi closed Fuse- In such a fuse the fuse element is placed in a semi closed carrier. Fuse carriers can be pulled out & the fuse element can be replaced, after the fuse operation. The carrier can be then placed in the fuse base.such fuses are very commonly used in our houses. 3. Cartridge Fuse This fuse is totally enclosed fuse. The fuse element is placed in a totally enclosed carrier with two Metal contacts provided on the two sides of a carrier. The entire cartridge is required to be replaced once fuse operates. 4. Drop-out Fuse S.R.C.O.E, PUNE Page 8

9 In such fuse, the fuse carrier drops out once, the fuse operates, the dropping out of fuse carrier provides the necessary isolation between the terminals. 5. Liquid Fuse When fuse operates, in case of high current there exists an arc. The arc must be extinguished properly. The fuse in which the arc is extinguished using a liquid medium is called liquid fuse. The liquid medium used is generally oil. The various types of liquid fuses are:- a) Oil break b) Oil expulsion fuse c) Oil blast fuse 6. Open Fuse This fuse consists of a plain fuse wire and the fuse operates any provision for extinguishing the arc. 7. Striker Fuse In this fuse, there exists a combination of a fuse and a mechanical device. When the fuse operates,strikes get released under pressure which gives the tripping indication. 8. Switch Fuse This fuse is a combination of a switch & fuse. The combined unit is called switch fuse. 9. HRC Fuse It is high rupturing capacity fuse. It is also called breaking capacity cartridge fuse. In such a fuse the arc is extinguished with the help of quartz, sand powder such a powder provides very high resistance which helps to extinguish the arc. It is basically a low voltage fuse which is used for various distribution purposes. DEFINITIONS: 1] Fuse The fuse is device which consists of a small piece of metal which is connected in series circuit when current through it increases beyond some predetermined value, the metal melts to interrupt the circuit current which protects the circuit from excessive high current. 2] Fuse element The part of the fuse which melts excessive current flows through it is called fuse element or fuse wire. 3] Current rating of wire It is that maximum current which fusing element can normally Withstand without any undue overheating or melting. It depends on: i) Temperature rise of fuse contacts of fuse holder ii) Fusing elements material S.R.C.O.E, PUNE Page 9

10 iii) Determination of fuse due to oxidation. 4] Fusing factor The ratio of the minimum fusing current & the current rating of fuse is called the fusing factor. As minimum fusing current is more than the current rating. The fusing factor is always greater than 1. 5] Prospective current The figure shows how the ac current is cut off using a fuse. This is called cut-off characteristic of fuse. The rms value of the 1 st loop of the fault current calculated if fuse is assumed to be replaced by a link of a negligible resistance is called the prospective current. 6] Cut-off current The current value at which the fuse melts before fault current achieve its peak value is called cut- off current. 7] Pre-arcing time The time between the commencement of the fault current and the instant when the fuse melts & the arc starts is called pre-arcing time. 8] Arcing time The time between the end of pre-arcing time and the instant when the arc gets completely extinguished is called arcing time. 9] Braking capacity The braking capacity is the fuse rating corresponding to the rms value of the ac component of maximum prospective current at its rated service voltage. 10] Pre-arcing (I 2 t) It is the time integral of the square of current passing through the fusing during pre-arcing time. 11] Arcing (I 2 t) It is the time integral of the square of the current through the fuse during the arcing time. 12] Clearing (I 2 t) It is the sum of the pre-arcing I 2 t and the arcing I 2 t is called clearing I 2 t or total I 2 t. 13] Voltage rating of fuse The voltage rating of fuse is specified by the manufacture. The rated voltage of the fuse must be equal or greater than i) Voltage of a single phase circuit ii) Line voltage in case of three phase circuit iii) Voltage between two outer wires in 3 wire dc circuit. CONCLUSION: In this way we have studied the different types of fuses. S.R.C.O.E, PUNE Page 10

11 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY OF FUSE & MCB & TESTING OF MCB EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/02(B) SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:-11 AIM : To study Miniature Circuit Breaker (MCB). CONSTRUCTION : As the name indicates, miniature circuit breaker is housed in moldings of insulating materials, which also has fire resistance property normally ceramic. The MCB consists of a bimetallic strip for thermal overload protection as well as instantaneous magnetic release type short circuit protection. These releases are fixed on each pole and in case of three phase circuit they are connected to common connecting base. FUNCTION : MCB automatically isolates the electrical circuit under sustained overload or short circuit. A bimetallic element provided on inverse time current characteristic which prevents interruption on normal inrush currents or temporary overload. An instantaneous magnetic trips release protects the equipments against very high currents. MCB s are available in 3 tripping circuit via B, C, D. Considering the fusing factor and aging effect of rewirablefuse, the smaller transformer of 25to 200 KVA will be better protected with MCB. OBSERVATION TABLE : Sr. No. Current Time in Sec CONCLUSION : Hence we have studied the working of miniature circuit breaker (MCB) and testing of miniature circuit breaker MCB is also performed successfully. S.R.C.O.E, PUNE Page 11

12 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY & TESTING OF CONTACTORS. LABORATORY MANUAL EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/03 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:12-17 STUDY & TESTING OF CONTACTORS. AIM: To study & test the contactors. APPARATUS: Switchgear testing kit, contactors & connecting wires etc. THEORY: Contactor is mechanical switching device capable of making, carrying & breakingelectric current under normal circuit conditions including operating overload conditions.acontactor is electromagnetically operated switches which can be operating remotely.contactor may be capable of making & braking short circuit currents, if they are designed for short circuit of emerging the control circuit namely. SOME TERMS & DEFINITIONS Electromagnetic contactor A contactor in which the opening & closing of main Contacts is achieved by means of an electromagnet. Electropneumatic contactor A contactor in which the force for closing & opening The main contacts is provided by an electrically opening pneumatic device. Main Circuit The conducting parts of the contactor designed to close & open. The current flows from the supply to load through the main circuit of the contactor. Main Contacts The contacts in the main circuit to carry the load current when the contactor is closed position. Control Unit The circuit which is energized or de-energized electrically for opening S.R.C.O.E, PUNE Page 12

13 /closing operation the contactor. Auxillry circuit The circuit other than main & control circuit is called auxillary circuit. PRINCIPAL: When a definite voltage is applied the coil energizes an electromagnet system comprising of fixed & moving parts, the moving parts get attracted to fixed part. Thus the electrical circuit is completed through this contact system. When magnet is de-energized, it gets pushed back by return spring & contacts open & thus electric circuit is broken. CONSTRUCTION OF TYPICAL CONTACTOR: Parts of contactor & their function: Rubber Padding:-It is provided for absorbing shocks during closing and opening the contactor. Magnets :- AC magnets are made up of laminations stacked together to reduce effect of eddy currents. Since in DC frequency is zero, problems of eddy currents losses & hysteresis losses do not exist & hence no laminations are required.there is designed gap between the central limb of fixed magnet & the moving magnet.when this gap reduces over millions of operations or magnet starts bulging it indicate thatmechanical life of contactor is over & needs replacement.if during maintenance or cleaning, emery or sand paper is used for the magnets the designedgap between the central limb increases as surface material reduces, increasing the air gap.hence while opening this remains some residual magnetic flux which does not allowthe moving magnet to separate immediately, causing severe pitting of contacts. This resultin frequent changing of contacts. Thus wage of emery or sand, paper should be avoided at magnets; it can be cleaned with CRC-2-26 / CTC & rough cloth. Contact System :- The contacts are made up of cadmium alloy. These have well anti welding properties. The gap between the contacts is less than that between magnets which ensures that contacts are S.R.C.O.E, PUNE Page 13

14 closed before magnet pole faces touch each other. LEAF Spring : - The moving contacts have to be held under certain contact pressure which is ensured by providing leaf springs over the contact carrier bridge. It also helps in bounce free closing Return Spring :- The moving assembly is held against the stored energy of two main springs called as return springs which helps the bridge assembly in opening the contact. Shading ring :- In A.C. magnets alternating flux (main flux) goes through natural zero point so force of attraction created becomes zero.this results in repeated de -energization of the magnets & leads to chattering.some additional force is require to hold the magnet when main flux passes through zero. It does this by generating an auxiliary flux which is out of phase with main flux, the shading ring is embedded in the pole face of the magnet for this. Terminals:- Terminals are made up of silver plated copper and are provided for both power circuit & control circuit terminators. Auxiliary contacts :- Set of normally open (NO) & normally close (NC) contacts are available for indication & alarm purpose. Arc Chute Set :- While breaking high currents between the contacts needs to be effectively quenched. Arc is quenched by following 3 methods: 1) Arc is split by providing number of Deion-plates. 2) The arc or current when drawn to Deion plates induces a voltage across the plates which 3) opposes the cause producing it. (arc) as per Lenz s Law 4) The resistance of the arc = specific resistivity x length of arc Area of arc S.R.C.O.E, PUNE Page 14

15 Due to splitting of arc its length increases as resistance of arc is directly proportional to length. The resistance of arc increases & thus arc is quenched. Housing :- Material having good thermal withstand and mechanical strength are used for housing. Mostly ceramic,smc ( sheet moulded compound ) & DMC (dough moulded compound ) are used for front housing while Die- cast. Aluminum is used for rare housing. SPECIFICATION OF CONTACTOR: 1) Rated Voltage 415 V 2) Rated coil voltage coils are available in various voltage rating eg.24,48,380,240,415 etc (AC/DC) 3) Contactor has following main current ratings & is selected as per the type of load ie. (application) Rated current for AC 1 Resistive load AC 2 Slightly Inductive load ( e.g. slip ring induction motor ) AC 3 Highly inductive load (e.g. Squirrel cage I.M. normal operation) AC 4 Inching & highly inductive load like squirrel cage induction motor. Contacts can be fitted with following accessories 1. Auxiliary contact blocks (add on block ) 2. Mechanical interlock etc. 3. Surge suppressor. Advantages of contactors: 1. High number of make- break operations 2. High making & braking capacity 3. Remote ON/OFF 4. High mechanical & electrical life Disadvantages of contactors: S.R.C.O.E, PUNE Page 15

16 1. It cannot sense fault itself. 2. It should be installed with relay unit. 3. Therefore it becomes costly. Applications of contactors: Remote controlling:- Mobile applications, Telecommunication, security, water pumps, green houses, remote power generator, solar systems, traffic control, field control, In agricultural industries where voltage is less & voltage fluctuations are more. Programming controllers. Voltage Monitors - They provide protection against phase loss, phase reversal.over, under & unbalanced voltage. It will also protect motor against voltagefaults. It will operate when voltage is exceeding the set value. Illumination control. 1. Timers 2. Starters Contactor starter from motor 1. D.O.L. contactor starter 2. Reversing contactor starter 3. / contactor starter 3. Air break contactors are used in L.V. switchgear. (suitable for large no. of switching operations on load/ over load ) 4. Key or push button. 5. Auxiliary switches. 6. Medium voltage vacuum contactors ( 3.6 to 12 KV)(suitable for controlling A.C. loads with high switching rate & unlimited on time) 7. Switching off - 3 Ø motor in A.C. 3 duty - Transformers - Capacitors - Resistive load (electric furnace ) S.R.C.O.E, PUNE Page 16

17 8. There is also an upcoming Biological contactor technology for Mine efficient treatment. PROCEDURE : 1) Check the rated voltage of contactor coil 2) Keep the contactor in vertical position. 3) Connect the coil terminals of the contactor to voltage output terminals of the test panel 4) For pick up voltage test, increases the voltage gradually till contacts close without humming. OBSERVATION TABLE: Rated Pick-up Drop-off Voltage (V) Voltage ( V) Voltage (V) V V V Current rating = A Pick up voltage = V (85 to 110 % of rated coil voltage) Drop off. Voltage = V (10 to 70 % of rated coil voltage) CONCLUSION: Thus we have observed the testing of contactor. It is rated for V& it s pick up & drop off voltage is V and V respectively. S.R.C.O.E, PUNE Page 17

18 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY & CHARACTISTICS OF THERMAL OVERLOAD RELAY EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/04 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:18-23 STUDY & CHARACTISTICS OF THERMAL OVERLOAD RELAY AIM : To study and test thermal overload relay. APPARATUS : Thermal overload relay ( 500 V, 50 Hz, 2 A AC ) Contactors Switch gear testing panel THEORY : Thermal overload relay prevent an electric motor from drawing excess current and overheating. Thermal overload conditions are the most likely faults to be encountered in industrial motor application, which produces an increase in the motors, Thermal dissipation and temperature. Overload protection prevents on electric motor from drawing excess current, overheating and finally bumping out. Thermal overload relays can be bimetallic relays, eutectic alloy relays, temperature control or probe relays and solid state relays. A bimetallic device is made up of two strips of different metals. The dissimilar metals are permanently joined. Heating the bimetallic strips causes it to bend because, the dissimilar metals expand & contracts at different rates. The bimetallic strips applies tension to a spring on a contact. It heat begins to rise the strip bends and spring pulls the contact apart breaking the circuit. A melting alloy ( or electric ) overload relay and a mechanical mechanism to activate a tripping device when an overload occurs. The relay measures the temperature of the motor by monitoring the amount of current being drawn. S.R.C.O.E, PUNE Page 18

19 This is done indirectly through a heater coil. Temperature control relays are used to protect the motor by directly sensing the temperature of the windings using thermister of RTD probes. The motor must have on or more positive temperature co-efficient thermister probes embedded in its windings. When nominal operating temperature of the probe is reached, its resistance increases rapidly. This increase is detected by a threshold circuit which controls a set of relay contacts solid state relays have no moving or mechanical parts. The relay calculates the average temperatures within the motor by monitoring its starting and running current. A solid state relay is also another type of over current relay. PRINCIPLE OF OPERATION : A bimetal is formed by two metals with unequal coefficient of linear expansion brazed together in the form of strip. When heated strip bends one end is fixed and other bends when heated under overload/ single phasing. CONSTRUCTIONS : The over current relay operates on thermal effect of electric current. Basically, it consist of a bimetallic strips. The bimetallic strip is nothing but two metal strips having different co-efficient of thermal expansion joined together. Here one end is supported and fixed and uneven expansion caused bending of strips. This operates the relay contacts. The fig. shows the construction of overload thermal relay. It consists of following parts Upper Slider bar :- One end of slider bar is connected to spring for pull action and other end is connected to spring for pull action and other end is connected to contact tripping level and top pivot points when bimetallic strip bends due to overload / unbalance current, this upper slider bar moves and pushes the contact tripping level, i.e. The upper slider bar is movable. Lower Slide bar :- S.R.C.O.E, PUNE Page 19

20 One end is connected to spring which has push action and other end is connected to bottom pivot point and contact tripping level. This bar has slots for carrying bimetallic strip. The spring apposes movement of contact tripping lever towards contact carrier i.e. lever slide bar is fixed one. Bimetallic strips :- It is made up of metal strips having different co-efficient of thermal expansion. They are three in number and housed in slots of lower slider. It gets supply from CT s for high currents. WORKING : Under normal conditions :- Strips are strained; contacts tripping lever is in vertical position and relay contacts are in normal position. Under overload condition :- Currents are greats than normal but balanced and hence all three bimetal and bend equally. The lower slider moves towards contact right and pushes control carrier. Hence NC contacts open which givessignal to the contactor and supply is cut off.suppose the R phase opens therefore any bimetals of Y and B phases operates due to bending of other two bimetals. Thus for the same power, the other two phase bimetals operates and trip the circuitproviding the single phasingproduction. Effect of over loading / over heating : The effect of overloading is an incipient fault which generally cause the damage of the insulation is supported to withstand certain temperature without damage. If the temperature increases beyond this for long periods, then the insulation deteriorates. The final stage is breakdown of insulation, thus this reduces the life of motor and so it becomes necessary to prevent this overheating due to overloading. Causes of overheating : Overload high current S.R.C.O.E, PUNE Page 20

21 Supply variation low voltage result in high current Heavy starting high starting current. High starting frequency motor is required to start often. High duty factor motor remains on for long periods and off for short periods. Single phasing complete load comes on two windings hence high current. Faulty bearings and other mechanical reasons. Defect in cooling systems for very large machines. Advantages of Thermal overload Relays : As the motor gets damaged due to higher temperature and causes of higher temperature are basically higher currents, the most commonly used protection is of current sensing devices, bimetallic thermal relay is used extensively. The main advantages are : Thermal overload relay gives protection for both balance and unbalance faults. They give protection against overloading & single phasing. The relay is compensated per ambient temp. variation from 5 c to 55 c so that it can protect the motor for both cold start & hot start condition These relays come as attachment with contactors They are quite economical. Application of Thermal Overload Relay : Overload Protection :- The relay protects motor against damage resulting from overloading as per international standard established for the protection of motor. Adjustment of relay to match the full load current of motor is a lever which moves against a calibrated scale marked in full load current. The range of current setting on any relay is between 100 % & 160 % of its minimum rating. Single Phasing Protection :- S.R.C.O.E, PUNE Page 21

22 The relay offers protection against single phasing, though, its sensitive differential mechanism in excess of the requirements of IEC specifications & trips even when it carries in healthy phases 0.9 times the minimum currents setting, regardless of the value to which the current adjustment lever is set. Full protection is provide on single phasing under varying operational load conditions up to 50 % of the full load rating of motor. No protection is required below the value. Direct coupling or free standing :- Incoming connectors are in the form of copper prongs that fir directly under the screw terminals. They can also be bent to a limited degree to suit the terminal position according to the type & contactor being used. When the relay is required free standing for separate mounting on additional inexpensive add-on terminal block is available. PROCEDURE : 1. For load connection, we connect the overload relay with contactor ( instead, we can use lamp.) 2. The three terminals of the overload relay are connected in series so that we can test the relay with Singlephase 3. The two terminals of the overload relay are connected to the switch-gear testing panel (0-50 A) 4. The connections from the relay to the testing panel are made as tight as possible. 5. The contactor coil is energized through the NC contact of the overload relay. Under normal operation condition the NC contacts (95 and 96) of overload relay remains NC which energises the coil of the contactor. Under overload condition, the relay trips ie. NC contacts of overload relay become NO which de-energises the contact coil & trips the contacts.then set the current more than rated value and for different current setting note down the trip time. S.R.C.O.E, PUNE Page 22

23 OBSERVATION TABLE : Current Setting Current (Amp.) Time (sec.) CONCLUSION : From the graph it can be concluded that as current increases the trip time decreases since it has inverse time characteristics. S.R.C.O.E, PUNE Page 23

24 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY CHARACTERISTIC OF IDMT RELAY /INDUCTION TO DIGITAL OVER CURRENT RELAY EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/05 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:24-27 STUDY OF CHARACTERISTIC OF OVER CURRENT RELAY AIM: To study the characteristic of over current relay. APPARATUS: Switchgear testing kit Over current relay Connecting cords. Screw driver. SPECIFICITIONS: Sr. No. Name of Equipment Variable AC current: Range 0-50 Amp. with 500 VA/1000VA Variable AC voltage: V AC, 2 Amps. Variable DC voltage: V DC, 2 Amps. Mains Input:(three terminal Normal 230V AC, 50 Hz, mains instrument plugs provided.) Outputs: Variable AC current source: 0-20A. Monitors: Other components: VA burden maximum: 200VA. Timer OFF connection from relay contacts. Time counter: Range: milli seconds with auto range. Accuracy: +/- 0.05%. Mains ON/OFF switch, Indication Lamps, Sturdy Current variable knob. S.R.C.O.E, PUNE Page 24

25 COMPLETE FUNCTION TESTING OF THE RELAY: Consist of the following instruments/ components, Current variable knob, relay IDMT EF 1 Pole, / Over Current relay, push button, timer, output terminals, etc. Procedure for Pick Up test :- 1) Connect the relay coil ( termination as ) to the current source (Terminated as ). as showm in the figure 1. 2) Connect the Aux. contact of the relay ( ) to the Timer contact of the kit ( ). 3) Connect the 230V AC supply to the kit. 4) Keep the Pick up setting at minimum position (50% i.e. 2.5A). 5) Switch ON the unit and push the Start Push button. 6) Now slowly increase the current value still relay operates i.e. Disc starts rotation or Pick Up LED Glow ON. 7) Note down the current value it must be equal to within +/- 10% of pick up setting. 8) Switch off the current source by pushing the stop Push button. 9) Reset the relay. 10) Repeat the procedure for the different pick-up setting i.e. 50 to 200%. 11) Switch OFF the mains supply. Procedure for Time Vs Current (IDMT)Characteristics test :- 1) Connect the relay coil ( termination ) to the current source (Terminated as ). as showm in the figure 1. 2) Connect the Aux. contact of the relay ( ) to the Timer contact of the kit ( ). 3) Connect the 230V AC supply to the kit. 4) Keep the TMS setting at maximum position (1 sec). S.R.C.O.E, PUNE Page 25

26 5) Keep the Phase setting plug at 2.5A (50%) Setting. 6) Switch ON the unit and push the Start Push button. 7) Now slowly increase the current value upto 3A by adjusting the current varaible knob. 8) Switch OFF the output by pushing the stop PB and reset the Timer without changing the setting. 9) Switch ON the output, which will also start timer. Timer will stop counting when the relay trips Note the delay. 10) Repeat the procedure for various current values as per table no ) Switch OFF the mains supply. Procedure for Testing TMS Setting:- 1) Connect the relay coil ( termination ) to the current source (Terminated as ). as showm in the figure 1. 2) Connect the Aux. contact of the relay ( ) to the Timer contact of the kit ( ). 3) Connect the 230V AC supply to the kit. 4) Keep the TMS setting at minimum position (0.1s). 5) Keep the Phase setting plug at 2.5A (50%) Setting. 6) Switch ON the unit and push the Start Push button. 7) Now slowly increase the current value upto 3.5A by adjusting the current varaible knob. 8) Switch OFF the output by pushing the stop PB and reset the Timer without changing the setting. 9) Switch ON the output, which will also start timer. Timer will stop counting when the relay trips Note the delay. 9) Repeat the procedure for various TMS setting values as per table no ) Switch OFF the mains supply. S.R.C.O.E, PUNE Page 26

27 Sample Table: Table no. 1.1: Pick-up test: TMS Setting: 1 Sec % Set (I >) Current in Amp. 2.5A (50%) 3.75A (75%) 5A (100%) 6.25A (125%) 7.5A (150%) 8.75A (175%) 10A (200%) Table no. 1.2: Time Vs. Current (IDMT) Characteristics for O/C or EF: TMS Setting: 1 Sec. Phase trip setting at 2.5A (50%) Phase trip setting at 3.75A (75%). Set current At Time in Sec. Set current At 3A 5A 5A 7.5A 7.5A 10A 10A 15A Time in Sec. Phase trip setting at 5A (100%). Set current At 7.5A 10A 15A 20A Time in Sec. CONCLUSION: S.R.C.O.E, PUNE Page 27

28 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY OF PERCENTAGE DIFFERENTIAL PROTECTION OF TRANSFORMER EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/06 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:28-29 STUDY OF PERCENTAGE DIFFERENTIAL PROTECTION OF TRANSFORMER AIM: To study the percentage differential protection of transformer. SPECIFICATIONS: Sr.No. Name of Equipment Range 1 AC Digital Voltmeter 500V,Aux. Supply of 230 V AC for Input Side 2 AC Digital Ammeter 5A,Aux. Supply of 230 V AC for Input Side 3 AC Digital Voltmeter 500V,Aux. Supply of 230 V AC for load Side 4 AC DigitalAmmeter 500V,Aux. Supply of 230 V AC for load Side TESTING OF DIFFERENTIAL PROTECTION TO TRANSFORMER: Connect: R3 TO R7&R5 TO R8 Y3 TO Y7& Y5 TO Y8 B3 TO B7&B5 TO B8 N3 TO N7&N5 TO N8 PROCEDURE: 1) Ensure all fault simulating switches in OFF position. 2) Switch ON the Mains MCB. 3) Push the Start Push button of Secondary side to give supply to input to transformer. S.R.C.O.E, PUNE Page 28

29 4) Primary Mains ON indication will glow and Voltmeter will show reading. 5) Push the start push button of secondary side and the load gets connected. 6) Secondary Mains on indication will glow and voltmeter will show the readings. 7) Now switch ON the fault simulating switch L-L fault. 8) Within a few micro seconds the fault will be created and the differential relay will protect the transformer by cutting OFF the mains supply to transformer. 9) As the relay get activated the mains supply will get cut OFF due to operation of contactor C2. 10) Now switch OFF the fault simulating switch and reset the relay. 11) Now repeat the above procedure from 3 to 10 for other faults like L-N fault and inter turnfault. CONCLUSION: S.R.C.O.E, PUNE Page 29

30 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY OF MERZ PRICE PROTECTION OF ALTERNATOR EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/07 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:30-36 STUDY OF MERZ PRICE PROTECTION OF ALTERNATOR AIM: To study the Merz Price Protection of Alternator. SPECIFICATIONS: Sr.No. Name of Equipment Range 1 AC Digital Voltmeter 750V, AC,Aux. Supply of 230 V AC 2 AC Digital Ammeter 5A,Aux. Supply of 230 V AC 3 DC Digital Voltmeter 750V, DC,Aux. Supply of 230 V AC 4 DC Digital Ammeter 20A, DC,Aux. Supply of 230 V AC 5 AC Frequency Meter Hz., Aux. Supply 230V AC Connect: Load Terminals R1 TO R2 Y1 TO Y2 B1 TO B2 N1 TO N2 S.R.C.O.E, PUNE Page 30

31 OPERATION INSTRUCTION: 1) Connect the Mains input of 1 Phase, 3 wire, 230V, AC to the demo panel, 15Amp. 1) Connect the Mains input of 1 Phase, 3 wire, 230V, AC to the demo panel, 15Amp. 2) Keep all the load switches & fault simulating switch in OFF position. 3) Connect the lamps for load bank. 4) Connect 1 Sq.mm. wire Red, Yellow, blue & Black to R, Y, B & N terminalsof alternator. 5) Connect blue tape red and black bunched to F & FF of field terminals of Alternator.. 6) Connect 1.5 sq.mm. Yellow & Blue to A & AA terminal of DC Motor. 7) Connect 1.5 sq.mm. bunched wire with blue tape to DC Motor Controller Terminalblock with similar colour. TESTING OF UNDER/ OVER VOLTAGE RELAY: For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 6) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 7) Now stable condition is achieved. 8) Now push the reset push button Green and Red both to reset the relays. 9) Now the load will get connected. 10) Now for Under Voltage protection reduce the Field Excitation of Alternator so that the Alternator voltage reduce to a value and the under voltage relay will trip and Under Voltage fault lamp will glow and the load gets disconnected. 11) Now again set the alternator field excitation upto normal voltage of 415V AC. 12) The Under/ Over Voltage relay get reset automatically. 13) Similarly for Over Voltage increase the field excitation to alternator and the Alternator output voltage increase at a over voltage vaule and relay will trip and the lamp will glow. 14) As the relay glow the load gets disconnected. 15) The relay get reset automaticaly. S.R.C.O.E, PUNE Page 31

32 TESTING OF UNDER/ OVER FREQUENCY RELAY: For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 6) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 7) Now stable condition is achieved. 8) Now push the reset push button Green and Red both to reset the relays. 9) Now the load will get connected. 10) Now for Under Frequency protection reduce the Armature Voltage to DC Motor and increase filed excitation of Alternator to maintain voltage, due to which speed of DC Motor reduces and hence Frequency reduces and the under frequency relay will trip. and Under Frequency fault lamp will glow and the load gets disconnected. 11) Now again set the alternator field excitation upto normal voltage of 415V AC and Armature voltage of DC Motor upto 208 V Frequency upto 50 Hz. 12) The Under/ Over Frequency relay get reset automatically. 13) Similarly for Over Frequency increase the Armature DC Voltage and decrease field excitation to alternator simultaneously and the Alternator output Frequency increase at a over frequency value the relay will trip and the lamp will glow. 14) As the relay glow the load gets disconnected. 15) The relay get reset automatically. Testing of Under/ Over Frequency Relay: For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. S.R.C.O.E, PUNE Page 32

33 6) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 7) Now stable condition is achieved. 8) Now push the reset push button Green and Red both to reset the relays. 9) Now the load will get connected. 10) Now for Under Frequency protection reduce the Armature Voltage to DC Motor and increase filed excitation of Alternator to maintain voltage, due to which speed of DC Motor reduces and hence Frequency reduces and the under frequency relay will trip and Under Frequency fault lamp will glow and the load gets disconnected 11) Now again set the alternator field excitation upto normal voltage of 415V AC and Armature voltage of DC Motor upto 208 V Frequency upto 50 Hz 12) The Under/ Over Frequency relay get reset automatically 13) Similarly for Over Frequency increase the Armature DC Voltage and decrease field excitation to alternator simultaneously and the Alternator output Frequency increase at a over frequency value the relay will trip and the lamp will glow. 14) As the relay glow the load gets disconnected. 15) The relay get reset automatically. Testing of Negative Phase Sequence Fault: Correct Connection: R1 TO R5 Y1 TO Y5 B1 TO B5 Fault Connection: R1 TO Y5 Y1 TOY5 B1 TO B5 For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Connect initially for correct connection and do below procedure. 5) Increase alternator filed supply upto 20% of scale. 6) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 7) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 8) Now stable condition is achieved. S.R.C.O.E, PUNE Page 33

34 9) Now push the reset push button Green and Red both to reset the relays. 10) Now the load will get connected. 11) For correct connection the relay will not trip. 12) For incorrect connection repeat the above procedure from 4) to 8). 13) As the Negative phase sequence is achieved hence the relay trip and the load does notget connected and the fault lamp glows. Testing of Over Current Relay: Connect: R1 TO R6 R7 TO R2 Y1 TO Y2 B1 TO B2 For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 6) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 7) Now stable condition is achieved. 8) Now push the reset push button Green and Red both to reset the relays. 9) Now the load will get connected. 10) Now switch ON the load switch. And increase the DC Voltage upto 208V DC and Alternator voltage to 415V AC. 11) Now switch ON the second load switch. 12) Moment the second load switch is switched ON the relay trips and the complete set gets cut OFF as the alternator is over loaded. 13) And the over current lamp will glow. S.R.C.O.E, PUNE Page 34

35 14) Now Set all the excitation and Armature Voltage to zero position and load switches to OFF position and reset the relay by pushing the reset push button. Testing of EARTH FAULT Relay: Connect: R1 to R10 N1 to N3 Y1 to Y2 B1 to B2 For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 6) Now against increase filed excitation of alternator upto 415V AC output on AC 7) Voltmeter. 8) Now stable condition is achieved 9) Now push the reset push button Green and Red both to reset the relays. 10) Now the load will get connected. 11) Now switch ON the load switch. And increase the DC Voltage upto 208V DC and Alternator voltage to 415V AC 12) Now switch ON the Earth Fault simulating switch. The moment the switch Turns ON the earth fault relay trips and the load gets disconneted. Switch OFF the fault switch immediately. 13) Switch OFF the load and reset the relay. Testing of Reverse Power Relay: Faulty Connections: R1 TO R8 R9 TO R2 Correct Connections: R1 TOR9 R8 TO R2 S.R.C.O.E, PUNE Page 35

36 Y1 TO Y2 & B1 TO B2 Y1 TO Y2&B1 TO B2 For Testing of Above Protection: 1) Ensure Zero at Armature Voltage and Field voltage Control knob at Zero Position. 2) Switch ON the Mains MCB. 3) Mains ON indication will glow ON. 4) Increase alternator filed supply upto 20% of scale. 5) Give DC supply upto 208V DC to DC Shunt Motor by Armature control knob. 6) Now against increase filed excitation of alternator upto 415V AC output on AC Voltmeter. 7) Now stable condition is achieved. 8) Now push the reset push button Green and Red both to reset the relays. 9) Now the load will get connected. 10) Now switch ON the load switch. And increase the DC Voltage upto 208V DC and Alternator voltage to 415V AC. 11) For correct connection the relay will not trip. 12) For incorrect connection repeat the above procedure from 4) to 10). 13) As the Reverse flow of current is achieved hence the relay trip and the load get disconnected and the fault lamp glows. CONCLUSION: S.R.C.O.E, PUNE Page 36

37 SHREE RAMCHANDRA COLLEGE OF ENGG. LONIKAND PRACTICAL EXPERIMENT INSTRUCTION SHEET EXPERIMENT TITLE: STUDY & TESTING OF MCCB LABORATORY MANUAL EXPERIMENT NO. : SRCOE/ELECT/BE/SGP/08 SWITCHGEAR AND PROTECTION (403147) DEPT. : ELECTRICAL ENGINEERING SEMESTER : II (BE) PAGE:37-38 STUDY & TESTING OF MCCB AIM: To study MCCB & testing of MCCB APPARATUS :3 pole,600v AC,50 A 5KA(Breaking current rating) Switchgear testing kit. THEORY :MCCB is used extensively in low voltage domestic, commercial, industrial applications. Tripping mechanism & the terminal contacts are assembled in a moulded case. When this circuit breaker goes out of service, it has to be placed with a new one. PROCEDURE: 1.Connect MCCB to be tested as shown. 2.Connect the 4 core cable provided at the back of switchgear testing kit to supply. 3.Switch ON the supply. 4.Reset the timer. 5.Push the ON push button provided on the front panel of the switchgear testing kit. 6.Using variac adjust the current greater than the rated current of MCCB. 7.Push OFF button. 8.Put MCCB in ON position & reset timer. 9.Again push ON push button. 10.See the timer & note down the reading of timer when MCCB trips. 11.Push the OFF push button. 12.Repeat the steps from4 to 11, for tracking more reading to plot the characteristics. S.R.C.O.E, PUNE Page 37

38 OBSERVATION TABLE : Sr.No Operating Current (A) Time of Operation(Sec) CONCLUSION: From the graph it is clear that current verses time of operation characteristics of MCCB are inverse nature. i.e. if the current through the MCCB is more,time of operation required is less& vice versa. S.R.C.O.E, PUNE Page 38

39 S.R.C.O.E, PUNE Page 39

40 S.R.C.O.E, PUNE Page 40

41 S.R.C.O.E, PUNE Page 41

42 S.R.C.O.E, PUNE Page 42

43 S.R.C.O.E, PUNE Page 43