Question

The basis of insulation design in modern EHV lines is:
1. switching voltage
2. power
3. current density
4. corona

Answer 1

Correct Answer - Option 1 : switching voltage

Concept:

• In extra-high voltage (EHV) transmission lines and power systems, switching surges is an important factor that affects the design of insulation.
• All transmission lines rated for 220 kV and above incorporate switching surge spark overvoltage for their insulation levels.
• A switching surge is a short duration transient voltage produced in the system due to a sudden opening or closing of a switch or circuit breaker or due to an arcing at a fault in the system.
• The waveform is not unique. The transient voltage may be an oscillatory wave or a damped oscillatory wave of frequency ranging from a few hundred hertz to few kilohertz.
• It may also be considered as a slow rising impulse having a wavefront time of 0.1 to 10 ms, and a tail time of one to several ms. Switching surges contain larger energy than the lightning impulse voltages.