The electrical field developed within clouds before a lightning stroke occurs can be of the order of

• 1.0 kV/cm

• 100 kV/cm

• 0.1 kV/cm

• 10 kV/cm

The velocity of wind currents required for charge separation inside the moving clouds is of the order

• 1 to 5 m/s

• 5 to 10 m/s

• 10 to 20 m/s

• 50 to 200 m/s

Overhead transmission lines are protected from lightning over voltages by

• counter poise wires

• protector tubes

• ground or shield wires above the main conductors

• shunt reactors

The material used in gap less surge arresters in HV power system is

• Graphite

• Zinc Oxide

• aluminum oxide

• Silicon carbide

The equivalent circuit of a surge arrester may be represented as

• non-linear resistor

• capacitor

• an inductor

• resistor

The peak value of lightning stroke currents are of the order

• 100 A

• 10 A

• 10 to 100 kA

• 1000 A

The over voltage surges in power systems may be caused by

• Lightning

• Resonance

• Switching

• All the choices

The dielectric strength of air at 25°C and 76 cm of mercury is

• 2.11 kV rms/cm

• 21.1 kV rms/cm

• 2.11 kV rms/m

• 21.10 kV rms/m

Corona effect can be identified by

• bushy sparks

• faint violet glow

• red light

• arcing between conductors and earth

Switching surge is

• high voltage dc

• high voltage ac

• short duration transient voltage

• hyperbolically dying voltage.