Control of Over Voltages due to Switching and Power Frequency
(a) Energization of TL in or more steps by inserting resistances and withdrawing them afterwards
- It is normal practice to have a series resistance with the circuit breaker contacts during switching ON and then but short circuiting this resistance after a few cycles.
(b) Eliminating or reducing trapped charges before reclosing
- By temporarily inserting resistors to ground or in series with shunt reactors and removing before closing of the switches the trapped charges that are left on capacitors and line conductors can be reduced.
(c) Phase controlled closing of circuit breaker
- By controlling the exact instances of the closing of the 3 phases separately over voltages’ can be avoided. But it requires complicated controlling equipment and therefore is not adopted.
(d) Use of shunt reactors.
(e) Limiting switching surges by suitable surge diverters.