Brekdown Phenomena
Breakdown of Gases: Charge multiplication,Secondary emission,Townsend Theory, Streamer Theory, Paschen’s Law,
Determination of Minimum breakdown voltage, Breakdown in non uniform field, Effect of polarity on corona
inception and break down voltage. Partial Discharge : definition and development in solid dielectric.
Break Down of Solids: Intrinsic breakdown, Electromechanical break down, Thermal breakdown, Streamer Breakdown.
Breakdown of Liquid: Intrinsic Break down, Cavitation Theory, Suspended particle Theory.
Lightning Phenomena: Electrification of cloud, Development of Lightning Stroke, lightning induced over
voltage, direct stroke, indirect stroke.
Protection of Electrical Apparatus against over voltage:
Lightning Arrestors, Valve Type, Metal Oxide arresters, Expulsion type. Effect of location of lightning arresters on
protection of transformer. Protection of substation, Earthwire.
Insulation Co ordination:
Basic Insulation level. Basic Impulse level, Switching Impulse level. Volt time characteristics of protective
devices, Determination of Basic Impulse level of substation equipment.
Generation of High Voltage
Generation of high a.c voltage by testing transformer, cascaded transformer, series resonant circuit, single stage
and multi stage. Advantages of Series Resonant Circuit in testing of cables
Generation of d.c high voltage: Cockcroft Walton doubler and multistage circuit.Definition of Impulse Voltage as
per Indian Standard Specification, Wave front and wave tail time ,Generation of Impulse Voltage, Multistage
impulse generator,triggering of Impulse Generator
Measurement of High Voltage:
Sphere gap voltmeter : a.c, d.c and impulse ,high voltage measurement as per Indian Standard Specifications.
Resistance and Capacitance Potential dividers, Peak voltmeters for measurement of high a.c voltage in conjunction
with capacitance dividers. Capacitance Voltage Transformer, Rotating Voltmeter for the measurement of d.c high
voltage, Electrostatic Voltmeter.
High Voltage testing: Testing as per Indian Standard Specifications: Power frequency
withstand, induced over voltage and impulse test on transformers, Power frequency wet withstand test and impulse
test on insulators.