Power System Engineering EEE228

Syllabus Unit 1 TL Parameters Unit 2 Modeling and performance of TLs Unit 3 Transmission systems Unit 4 Insulators and Cables Unit 5 Distribution system Unit 6 substation practice

Unit 1 TL Parameters Parameters of single and three phase transmission lines with single and double circuits: Resistance, inductance and capacitance of solid, stranded and bundle conductors Symmetrical and unsymmetrical spacing Transposition Application of self and mutual GMD Skin and proximity effect Inductive interference with neighboring circuits. Typical configuration ,conductor types and electrical parameters of 400,220,110,66 and 33 kV lines

Power System Network

Power Grid / Load Dispatch Centre

Load Dispatch Centre Five Load dispatch centre Eastern Region Load Despatch Centre, Kolkatta North Eastern Region Load Despatch Centre, Shillong Northern Region Load Despatch Centre, New Delhi Southern Region Load Despatch Centre, Bangaluru Western Region Load Despatch Centre, Mumbai

Total Installed capacity Total installed capacity in India is 167 GW.

Power Demand 17th Electrical Power Survey of India, 2007[1,2] – Power demand rise to peak value of 153 GW (1,52,746 MW) by 2011-12. – India needs a generation capacity of at least 200 GW (2, 00,000 MW) to be installed by 2012 from the present level of 114 GW (1, 14,000 MW) McKinsey & Company’s - “Powering India: The Road to 2017” [3, 4] – India grows at an average rate of 8% for the next 10 years – Power demand likely to soar from around 114 GW at present to 315 to 335 GW by 2017. – Needs generation capacity of 415 to 440 GW – 4 key factors behind the analysis are:[3, 4] Two Surveys are made on India’s future power demand for 2012 and 2017. India’s power demand will raise to 153 GW by 2012. That means India needs generation capacity of 200 GW. By 2017, power demand will raise to 335 GW. That means need of generation capacity is 440 GW. Apart from demands, GOI has an ambitious mission of electrifying all rural areas by 2012. Thus further increases the power demand. (i) Rise of industrial power demand, (ii) Commercial demand rising at 14% over the next 10 years, (iii) ‘Power for all by 2012’ and (iv) the realization of demand suppressed due to load shedding “Power for all by 2012”– goi, 2008 [2] – Electrification of all rural areas

Transmission line World's Leading Power Transmission Utility - 79556 Ckt.Km line has increased from 3708 ckm in 1950 -132 Substations as on Sept 30,2010 Transmission lines at 800/765 kV, 400 kV, 220 kV & 132 kV EHVAC & +500 kV HVDC levels About 51% of total power generated in the country is wheeled through this transmission network

TL Parameters All transmission lines in power system exhibits electrical properties of R, L, C & g L and C are due to effects of electro magnetic and electro static fields around the conductors Shunt conductance accounts for leakage currents flowing across insulators and ionized path in the air. But leakage currents are negligible compared to the current flowing in the TL.

Solid, stranded and bundle conductors Solid conductor Less flexibility Less strength Normally used for Lowcapacity Stranded Conductor Alternate layer spiralled opp. to prevent unwinding Cheaper Lighter than cu. Less conductivety Less tensile st. Because of less cond. and density results large dia. and reduced electric stress. Hence Corona free ACSR Steel--High tensile st. Bundled conductor Most effective way of constructing corona free EHV Several conductors/phase

Benefits of Bundled Conductor

Effect of magnetic fields on TLs If a conductor is carrying high alternating currents, the distribution of current is not evenly dispersed throughout the cross section of the conductor due to magnetic field effect. This effect is classified as skin and proximity effect. Factors : Nature of material, Freq. of the system, Diameter of wire, Shape of wire

Skin Effect If the conductor is composed of one or more concentric circular elements, then the centre portion of the conductor will be enveloped by a greater magnetic flux than those on the outside. Consequently the self induced back-emf will be greater towards the centre of the conductor, thus causing the current density to be less at the centre than the conductor surface. This extra concentration at the surface is known as skin effect, and results in an increase in the effective resistance/reactance of the conductor. Skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core.

Proximity Effect The proximity effect also increases the effective resistance/reactance and is associated with the magnetic fields of two conductors which are close together. If each carries a current in the same direction, the halves of the conductors in close proximity are cut by more magnetic flux than the remote halves. Consequently the current distribution is not even throughout the cross-section, a greater proportion being carried by the remote halves. If the currents are in opposite directions, the halves in close proximity will carry the greater density of current.

Interference with neighboring circuits Electrostatic and electro magnetic fields produced by TL conductors are having certain freq. and magnitudes. Because of these fields, voltage and current are induced in the neighboring circuits (communication circuits). Potential of the communication circuits are raised by electrostatic field effects Electro magnetic field effect introduces current in the communication circuits along with speech signals. These effects are mainly depends on the distance between two lines. Steps to reduce interference: Parallel run should be avoided. Use greater spacing between power and communication. Better use under ground system for any one line. Otherwise change the communication system into microwave/carrier wave/fiber optical type.

Unit 2 Modeling and performance of TLs Classification of lines: Equivalent circuits for short, medium and long lines Attenuation constants, phase constant, surge impedance Transmission efficiency and voltage regulation Real and reactive power flow in lines: Power angle diagram Surge impedance loading loadability limits based on thermal loading, angle, voltage stability considerations Shunt and series compensation Ferranti effect and corona loss

Unit 3 Transmission systems Mechanical design of transmission lines Line sag, string chart, line support, conductor material, economic considerations of the transmission line overhead line versus underground line.

Unit 4 Insulators and Cables Types, Voltage distribution in insulator string and grading , improvement of string efficiency. Cables: Constructional features of HT & LT cables, dielectric stress and grading , Thermal characteristics

Unit 5 Distribution system Different types of distributors – Selection of conductor sizes – radial and ring main systems – DC three wire systems – single fed and multi fed distribution systems ;

Unit 6 substation practice Types of substations,- equipments in the substation - bus bar arrangements – substation protection against over voltages

References Text books: D.P.Kothari, I.J. Nagrath, Power System Engineering, Tata McGrawHill Publishing, 2nd edition, 2008. V.K. Metha, Rohit Metha, Principles of Power system, S. Chand, 4th revised edition. Syed A. Nasar, Electric Power Systems, Tata Mc Graw Hill Publishing. References:William Stevenson, Elements of power system analysis”, Mc Graw Hill Company, 4th edition.I.J.Nagrath and D.Kothari,”modern power system analysis” Tata mc graw hill 2nd edition.C.L.wadhwa,’Electrical power system’, new age publications, 1998.Turan gonen, ’Electrical power distribution system engineering www.pgcil.com www.ntpc.org www.cpri.org