Imran Ali Assistant Manager at Chashma Power Plant

When a command for Breaker close is generated, what common interlocks are observed, in other words which conditions are generally true or false to issue a close command for a CB??

Jari Vertanen Hello Imran! CB close block can be made in mechanical, hardwired or in relay configuration if close command is given via relay. Needed blockings depends about scheme, type of feeder & way customer use network and it's hard to say that do it always like this. Here is some conditions need to be true: -disconnector/truck not in middle position (disconnector should never connect load)

-CB Spring charged (this block is normally made inside CB)

-SF6 pressure not in low-low level (this block is normally made inside CB)

-synchrocheck not blocked (eg. measuring fuses OK)

-synchrocheck OK

synchrocheck can be also synchronizing in case of generator CB

This depend on the C.B it self . Is it( generator C.B or medium voltage C.B or low voltage C.B or.....). Please Mr Imran tell us the function of this C.B.

-Trip Circuit Supervision (TCS) alarm (if used) should also block CB close

-protection no active trips

-Sometime protection trip need local reset before close is possible (somebody to inspect situation, eg. arc fault trip should be latched type and block close cmd)

-thermal protection (cable/motor) cooling below alarm level

-motor too often start block not true

-capacitors need discharge time and we have to wait that before close

-Often in transformer feeders is so that HV side breaker need close first

-For bus tie breaker we need to prevent reverse supply and switching against fault

slava g To Jari's explanation possible add only special cases.

Manrique Murillo when using manual operated disconnectors it is useful to be sure that it is not half a way open or closed (indeterminated state) before closing

Mohsen Esmaeili Following signal should block closing command, too: "circuit breaker failure start"