Question

valve house and converter station is mostly subjected to the following overvoltages

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Answer 1

short switching impulse

Answer 2

Answer:

The correct over voltages to which the valve houses and the converter stations are subjected to is found to be: Short Switching impulse.

Explanation:

• A distinction is made between lightning pulses and switching pulses based on the  duration of the wave front. Pulses with a wave front duration of up to  tens of microseconds are generally considered  lightning pulses.
• The switching pulse test is run when the device voltage is above 345KV or specified. The basic switching pulse level (BSL) is specified in the standard. For standard switching pulse waveforms, the time to crest is at least 100 ps, ​​the time to the last first zero  is at least 1000 ps, ​​and the time above 90% of the voltage crest level is at least 200 ps.
• The  voltage crest level tolerance is ± 3%. Recommended sweep times are 150-250 ps for front time, 500 ps for voltages above 90%, and 1500-2500 ps for  the first zero. The switching pulse builds  a magnetic field in the core due to its long tail and  open circuit from the non-pulse terminal. This can saturate the core and reduce the time to the first zero voltage to less than 1000ps. Also, the reduced wave can have a different  shape than the full wave. This effect is minimized by magnetically biasing the core in the opposite direction before  the full wave is applied.

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