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

Overhead transmission lines are protected from lightning over voltages by

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

The equivalent circuit of a surge arrester may be represented as

The peak value of lightning stroke currents are of the order

The over voltage surges in power systems may be caused by

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

Corona effect can be identified by

Switching surge is

Main cause of momentary excessive voltages and current are

1. Lightning

2. Switching

3. Short circuit

4. Resonance

Out of these the most common and most severe causes are

The reflection of surges at open ends leads to voltage build up, which may eventually damage the high voltage equipment

Characteristic impedance of transmission line depends upon

In case the characteristic impedance of a transmission line is equal to the load impedance

For reducing tower footing resistance it is better to use

An electronegative gas is one in which

Ionization coefficients α, γ are functions of

Paschen’s law states that

tan δ for liquid insulants at 50 Hz should be less than

The parameters that affect the breakdown strength of liquids is

The effective inductance and capacitance of a faulted system as viewed from the contacts of a breaker are 2.5 mH and 600 µF respectively. Determine the re-striking voltage across the breaker contacts when a fault current of 150 A is chopped.

In a 132 kV system, reactance and capacitance up to the location of the circuit breaker is 5Ω and 0.02µF respectively. A resistance of 500Ω is connected across the contacts of the circuit breaker. Determine the critical value of resistance

A 3 –phase single circuit transmission line is 400 km long. If the line is rated for 220 kV and having R = 0.1 ohm/km, L= 1.26 mH/km and C= 0.009 µF/km, calculate the surge impedance of the transmission line

What will the breakdown strength of air be for small gaps (1 mm) and large gaps (20 cm) under uniform field conditions and standard atmospheric conditions?

A solid specimen of dielectric has a dielectric constant of 4.2 and tan δ = 0.001 at a frequency of 50 Hz. If it is suitable to an alternating field of 50 kV/cm, calculate the heat generated in the specimen due to the dielectric loss.