High Voltage (HV) Interview Questions Answers

Why Earth Wire is provided in the overhead transmisssion lines?

Answer: Earth wire is provided above the overhead transmission lines for protection against lightning strokes. The ground wire or earth wire protects the phase conductors or line conductors by attracting itself the lightning strokes which in its absence would strike the phase conductors. Also the ground wire reduces the voltage electrostatically or electromagnetically induced in the conductors by the discharge of a neighboring cloud. It also provides the additional protective effect by causing the attenuation of traveling waves set in the lines by acting a short circuit secondary of the line current

What is meant by protective angle? Give its value for reliable operation?

Answer: Protective angle is the vertical angle through the ground wire axis and the line passing from the ground wire axis to the outermost phase conductor. Its value for reliable protection is taken equal to 20-30 degrees

What is the difference between the lightning arrester and surge absorber?

Answer: Lightning arrester limits the duration and amplitude of the follow current while a surge absorber reduces the steepness of the wave front for a particular surge

What is meant by Lightning arrester or surge diverter?

Answer: A Surge Diverter is a device that is connected between line and earth, i.e, in parallel with the equipment under protection at the substation. It limits the duration and amplitude of the follow current 

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What is meant by impulse ratio of any lightning arrester?

Answer: Impulse ratio of any lightning arrester is the ratio of breakdown voltage of the wave of special duration to breakdown voltage of a 50Hz wave

What is meant by voltage surge?

Answer: Voltage surge is sudden excessive rise in voltage that may be dangerous to the electrical equipment of an installation. Voltage surge cause damage to insulation of the system. Voltage surges are caused because of lightning, switching on and off the load at high voltages

How standard lightning impulse wave is represented?

Answer: Standard Lighting impulse wave is represented by 1.2/50 micro sec wave