Switch Gear and Protection
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY
III Year B.Tech EEE II-Sem T P C
4+1* 0 4
SWITCH GEAR AND PROTECTION
This course introduces all varieties of Circuit Breakers and Relays for protection of Generators,
Transformers and feeder bus bars from over voltages and other hazards. It emphasis on Neutral
grounding for overall protection.
UNIT – I Circuit Breakers-1
Circuit Breakers: Elementary principles of arc interruption, Recovery, Restriking Voltage and Recovery
voltages.- Restriking Phenomenon, Average and Max. RRRV, Numerical Problems – Current Chopping
and Resistance Switching – CB ratings and Specifications : Types and Numerical Problems. – Auto
UNIT –IICircuit Breakers-2
Description and Operation of following types of circuit breakers: Minimum Oil Circuit breakers, Air Blast
Circuit Breakers, Vacuum and SF6 circuit breakers.
UNIT – III Electromagnetic and Static Relays
Principle of Operation and Construction of Attracted armature, Balanced Beam, induction Disc and
Induction Cup relays.
Relays Classification: Instantaneous, DMT and IDMT types.
Application of relays: Over current/ Under voltage relays, Direction relays, Differential Relays and
Percentage Differential Relays.
Universal torque equation, Distance relays: Impedance, Reactance and Mho and Off-Set Mho relays,
Characteristics of Distance Relays and Comparison.
Static Relays: Static Relays verses Electromagnetic Relays.
UNIT – IV Generator Protection
Protection of generators against Stator faults, Rotor faults, and Abnormal Conditions. Restricted Earth
fault and Inter-turn fault Protection. Numerical Problems on % Winding Unprotected.
UNIT –V Transformer Protection
Protection of transformers: Percentage Differential Protection, Numerical Problem on Design of CT s
Ratio, Buchholtz relay Protection.
UNIT –VI Feeder and Bus-Bar Protection
Protection of Lines: Over Current, Carrier Current and Three-zone distance relay protection using
Impedance relays. Translay Relay.
Protection of Bus bars – Differential protection.
UNIT – VII Neutral Grounding
Grounded and Ungrounded Neutral Systems.- Effects of Ungrounded Neutral on system performance.
Methods of Neutral Grounding: Solid, Resistance, Reactance – Arcing Grounds and Grounding Practices.
UNIT – VIII Protection against over voltages
Generation of Over Voltages in Power Systems.-Protection against Lightning Over Voltages – Valve type
and Zinc-Oxide Lighting Arresters – Insulation Coordination -BIL, Impulse Ratio, Standard Impulse Test
Wave, Volt-Time Characteristics.
1. Switchgear and Protection – by Sunil S Rao, Khanna Publlishers
2. Power System Protection and Switchgear by Badari Ram , D.N Viswakarma, TMH Publications
1. Fundamentals of Power System Protection by Paithankar and S.R.Bhide.,PHI, 2003.
2. Art & Science of Protective Relaying – by C R Mason, Wiley Eastern Ltd.
3. Electrical Power Systems – by C.L.Wadhwa, New Age international (P) Limited, Publishers, 3nd editon
4. A Text book on Power System Engineering by B.L.Soni, Gupta, Bhatnagar, Chakrabarthy, Dhanpat Rai & Co.