Electrical Power System A Review

Transcription

1 IJSTE - International Journal of Science Technology & Engineering Volume 3 Issue 01 July 2016 ISSN (online): X Electrical Power System A Review Mohan Kumar N B. Kantharaj M. Tech Scholar Associate Professor Poshitha B Manaswi K. J. Assistant Professor Assistant Professor Abstract This paper presents brief info s about Electrical Power System, i.e. Generation, Transmission and Distribution of Electrical Energy. Includes current Indian installed capacity, line to line and ground distance in transmission lines at different voltage levels. Vector groups of transformers, FACTS application in power system, HT, LT cable sizes and current carrying capacity available for the distribution of electrical power/energy. Also the names of company are manufacturing Electrical Power System (Switch Gear) equipment s. The contents of paper may help in industrial/non industrial sector for system reading and to the people, who are willing to start their career in electrical power system engineering. Keywords: RES, FACTS application, CEA I. INTRODUCTION Electrical power/energy, it is the most widely used generated source in the world today. Effects directly to the development of any country. As the standard of living can be related to the utilization of power, we can t imagine the life without electrical power. Electrical power is generated by means of, Hydro power Thermal power Nuclear power Hybrid power (combination of wind & solar)(res) Diesel power Gas power These are depending on various sources like water, coal, uranium, wind & solar energy (R.E) and petroleum products. Electrical power is generated at 11 KV & stepped up to 220 KV or 400 KV in step up transformer and transmitted to various parts of the country through transmission lines with the help of Grid. (Grid - interconnection of two or more transmission lines from the sources, to assure continuity power supply and stabilization). The power transmitted from EHV & HV overhead lines is stepped down to 33 or 11 KV in step down transformers for distribution purpose. And at the consumers end, it is again stepped down to 415 volts in distribution transformer for utilization purpose (power distribution is done through LT overhead lines). [2-3] Table 1 All India installed capacity (IN MW) of power stations (As on May 2016), 1 Total thermal 2,11, Nuclear 5, Hydro 42, RES 42, Total 3,03, Table 2 Total thermal 1 Coal 1,86, Gas 24, Diesel Total thermal 2,11, Most of the Power generation is done at 11 KV, generating energy at 100 % of installed capacity is not possible due to the limitation in sources/status of the plant etc. And the generated power/energy will not be the same at consumers or at distribution end, it is due to, All rights reserved by 63

2 Losses in transmission & distribution lines. Transmission & distribution losses are about 25% & power deficit is about 10% in India, Works are going on to reduce transmission and distribution losses, as per the utilization losses are concerned, that is fully dependent on the consumers. Present transmission voltage levels in India are, 66KV, 110/132 KV, 220KV and 400KV HVAC. Distribution is done in 33KV, 11KV and at 415 V (all voltage levels in 3 Phase only) respectively. With star-neutral configuration in distribution transformers, power is supplied to the consumers at 230 Volts (1 Phase). Transmission line clearance between line to ground and line to line (under worst sag conditions), these values offers minimum value which is to be maintained as per CEA rules, In general, for voltages up to 33KV min distance between lines to ground is Meters (12 Feet). For voltages above 33KV is Meters (12 Feet) plus Meters (1Feet) for every additional 33KV or part thereof. Horizontal clearance between lines or any part of abstractions up to 11 KV is min Meters (4 Feet), for 33KV is min Meters (6 Feet) and above 33 KV is Meters (6 Feet) plus Meters (1 Feet) for every additional 33KV or part thereof. Table 3 Minimum clearance between live parts and ground is as follows, Voltage (KV) (HVAC) Clearance Phase-earth Meters Clearance Phase-phase Meters Safety Clearance Meters / As we know that electrical power system consists of number of equipment s (from Generation to Distribution) includes, Generators, Transformers, Switch Gear Accessories, Transmission and distribution Towers and its accessories, System Automation controllers, Facts Devices, IT integration to monitor and control of system at each stage etc. All these equipment s are used in power system to control and operate the system, by maintaining its stability according to constraints. This is done to ensure quality power/energy and reliability to the consumers. In above said equipment s, transformers plays link role between each stages of power system to transfer the energy to consumers. Since power system in India is operating with one grid, entire system is operation is done in parallel mode. Table 4 Vector group info s for parallel operation is given below, Group 0 clock T C Group 1 0 o clock 0 delta/delta, star/star Group 2 6 o clock 180 delta/delta, star/star Group 3 1 o clock -30 star/delta, delta/star Group 4 11 o clock +30 star/delta, delta/star [7] Negative sign indicates LV is Lagging HV and Positive sign indicates LV is Leading HV. Transformers belonging to same group can be operated in parallel without any difficulty, parallel operation of transformers from Group 1 or 2 with Group 3 or 4 is not possible due to phase shift difference and if it is done, then results in circulating currents in local circuit. Leads to increased losses, unequal load sharing, over heating of transformers, further contributes to faults in power system etc. However parallel operation transformers in group 1 and 2 is possible by changing internal connection at the secondary winding of any one transformer. Similarly parallel operation of transformers of Group 3 and 4 is possible by modifying external connection of secondary winding of any one transformer to bring phase shift to Zero. Transformer vector Groups, Phase shift connection 0 Yy0 Dd0 Dz0 30 Lag Yd1 Dy1 Yz1 60 Lag -- Dd2 Dz2 120 Lag -- Dd4 Dz4 150 Lag Yd5 Dy5 Yz5 180 Lag Yy6 Dd6 Dz6 150 Lead Yd7 Dy7 Yz7 120 Lead -- Dd8 Dz8 60 Lead -- Dd10 Dz10 30 Lead Yd11 Dy11 Yz11 [7] Capital letter in vector group notation, always indicates primary winding of the transformer (usually represents HV winding). Example: Yd11 Means, transformer primary is in star connection, secondary is in delta connection and secondary voltage leads primary voltage by 30. Depending on system configurations and requirements vector group of transformer is selected for application. All rights reserved by 64

3 From past few decades, there is rapid development in power system to improve system stability (transient and steady state), this is done to improve system reliability and to assure quality power to the consumers. The development in power system is achieved/ing by the integration of FACTS Devices and IT integration in to it. In addition to this efficient equipment s implementation at each stage of power system is also a considerable factor in development in power system. Comparing to the efficient equipment s (to carry real power in the network). FACTS devices impact, has become more predominant. This is due to following advantages, 1) Smooth precision control of reactive power flow in the network. 2) Excellent voltage support at load buses. 3) Flexible in integration to IT for system automation and control. 4) Doesn t contribute to system faults. 5) Improves dynamic and steady state stability of the system. 6) Increases power flow capacity of the transmission and distribution network (at no load). 7) Reduction in negative phase sequence loading. 8) Reduces system losses and increases real power flow in the network (on load). 9) Improves system life and provision for real power exchange in the network. 10) Improved system efficiency, power quality and reliability. Some of the FACTS (Flexible Alternating Current Transmission System) Devices used in power system are, SVC Static Var Compensator. TCSC Thyristor Controlled Series Capacitor. UPFC Unified Power Flow Controller. STATCOM Static Synchronous Compensator. SPST Static Phase Shifting Transformers. SSSC Static Synchronous Series Capacitor. IPFC Interline Power Flow Controller. TCV L/R Thyristor Controlled Voltage Limiter/Regulator. TCBR Thyristor Controlled Braking Resistor TSC/TCC Thyristor Switched Capacitor/ Thyristor Controlled Capacitor, etc. Useful equations in three phase network are given by, Three phase power flow equations, P = 3 V I Cos Ф Q = 3 V I Sin Ф KVA = ( KW 2 + KVAR 2 ) KVA = KW / Cos Ф. V L-L = 3 Vph (Star network). I L-L = 3 Iph (Delta network). Power flow equations for transmission network under compensation are given by, Series compensation. P = Vs Vr sin Ȣ / Zn sin Ѳ (1 Kse). Kse = Xc / (2Zn tan Ѳ/2) Where, Vs = sending end voltage (KV). Vr = receiving end voltage (KV). Ȣ = power angle of transmission network (Lies between 0 90, optimum value ). Zn = surge impedance of the line = (L / C) ohms. Kse = degree of series compensation. Xc = reactance of series compensation. Ѳ = phase angle difference between line and injected voltage by the compensator (Lies between 0-30 ). Qse=(V 2 sinȣ/2/((zn 2 sin 2 Ѳ/2)(1 Kse 2 )))(Xc) Qse=reactive power flow after series compensation. Shunt compensation. P = Vs Vr sin Ȣ / Zn sin Ѳ (1 Ksh). Ksh = ((Bc Zn/2) tan Ѳ/2). Where, Vs = sending end voltage (KV). Vr = receiving end voltage (KV). All rights reserved by 65

4 Ȣ=power angle of transmission network (Lies between 0 90, optimum value ). Zn = surge impedance of the line = (L / C) ohms. Ksh = degree of shunt compensation. Bc=susceptance of shunt compensation. Ѳ = phase angle difference between line and injected voltage by the compensator (Lies between 0-30 ). Qsh = ((V 2 cos Ȣ/2)/ (Cos 2 Ѳ/2(1-Ksh 2 )) (Bc) Qsh=reactive power flow after shunt compensation. Power flow equations for distribution network under compensation are given by, KVAR req to improve power factor, KVAR new= KW (tan Ф1-tan Ф2). Where, tan Ф1= tan (cos -1 Ф1). tan Ф2= tan (cos -2 Ф2). cosф1= old power factor. cos Ф2= new power factor. % voltage raise = KVAR new / KVAsc. KVAsc= short circuit capacity of the network at compensating equipment. = KAsc* KV L-L*1.732 Or KVAsc Transformer KVA rating / Transformer per Unit Impedance. [4] Available power cable sizes (sq-mm) to carry current in the network (1, 2, 3, 3 1/2, 4 cores etc.), 1,1.5,2.5,4,6,10,16,25,35,50,70,95,120,150, 240,.300,400,500,630,800,1000 Operating voltage ranges available, 1.1 KV, 3.3 KV, 6.6 KV, 12 KV, 33 KV. Current capacity of the cable depends on various factors like, current density, type of laying, insulation quality, type of cooling, real and reactive power flow in the network, negative phase sequence loading, type of protection, system/network grounding etc. Current density of the cable decreases with the increase in cable size, so as the current carrying capacity of the cable. This is because, current density = I / area of the cable in sq-mm. In general, for cable sizes between 1.0 sq-mm to 120 sq-mm, current density value can be taken in the range 5.0 to 2.5 to find the current carrying capacity of the cable (for continuous loading). And for cables sized between 150 sq-mm to 1000 sq-mm, current density value can be taken between 2.0 to 075 to find the current carrying capacity of the cable. Protection schemes employed in power system to safeguard the equipment s and safety of the personal operating the system, Since electrical power system comprised of many switch gear equipment s, arranged and operating according to the requirements. System is to be protected against unpredictability s, i.e. System faults. Some of the protection schemes employed are (in general, open circuit and short circuit protection), Over current protection. Earth fault protection. Over/under voltage protection. Over/under frequency protection. Protection against negative phase sequence loading, over load, high winding temperature. Directional and non-directional power and current flow in the network. Generator and transformer differential current protection. Protection against loss of excitation in generators. Transformer buchholtz protection. Protection against feedback failure etc. Some of the Companies, producing electrical power system equipment s are, BHEL, SIEMENS,TDPS, Alternator/D G ABB, Kirloskar Electric, VA TECH, G E etc. Transformers ABB, KAVIKA, C G, EMCO,DELTA VOLTAMP, etc. ABB, SIEMENS, Motors Kirloskar Electric, G E, BBL, C G etc. Switch Gear Equipment s L&T,ABB, SIEMENS GE, BBL, AREVA, All rights reserved by 66

5 ( HT & LT breakers, Relays, CT s,pt s, Measuring instruments, power & control Contactors, Isolators, Connectors, Controllers etc. Power and control cables Variable Frequency Drives System software Developers Schneider Electric, HAVELLS, Toshiba, V-Guard etc. Polycab, Standards, V-Guard, Havells etc. ABB, Toshiba SIEMENS, Hirel, G E Schneider Electric etc. Honeywell,GE Yokogova, Forbes Marshall, ABB, SIEMENS, Allen Bradley, etc. [1 7] II. CONCLUSION Electrical power system is a complex network & one of the fast growing systems in the world today. This has become a mandatory aspect to lead life and due to the application severity, there is a need to recall system basics, which are useful in enhancing system knowledge and helps in adapting to new emerging technologies/innovations. In this paper, an attempt is made on electrical power system review. Hope the contents of the paper are useful to the people of power system in industrial / non industrial sector and helps at least to some extinct in their profession. [1] [2] V K Mehta - Principles of power system (Latest edition 2014). [3] S S Rao Switch Gear and Protection (Latest edition 2014). [4] K R Padiyar FACTS controllers in power transmission and distribution. [5] Electrical power system Equipment s producing Company s. [6] [7] technology.org REFERENCES All rights reserved by 67