400 V Switchgear Panel Trip All the Way Up to 6.6kV Switchgear Panel

If the 6.6kV panel trips then it is very difficult to see why a trip at the 400V panel could occur, as there would be no power on it as a result of the 6.6kV trip.

On the other hand, working back upward, loss of 400V power could be used via a shunt-trip breaker to then interrupt the 6.6kV power.

Not possible to trip but to interlock the switch gear.

I would though look at all the systems the 6.6kv switch gear powers. That you may not be creating a hazard for personnel if it shut down.

Yes, you can trip the 6.6kV Panel if there is any fault in the 400V Distribution network through Relay Co-ordination.

But still, it is hard to understand that why you want to trip 6.6kV Network ,instead of 400V Distribution Circuit.

You can have much precise and selective trippings in 400V Network and will be easy to troubleshoot also.

I recently altered the tripping on an 11/.66KV system. The fault currents on the LV side were so large that I got the MV side to clear the fault first.

I inherited this system, it was terrible. The LV ACB was loaded to the max at 4000A, I didn't want that tripping under fault. So a bit of jiggery pokery on the MV side got that to clear the fault first.

I was stood next to an ACB when it opened under fault, I had to go and change my underwear!

The entire room lit up.

This is scary.

The upstream protectioin should be designed to protect the power conductors between the MV and LV switchgear.

The LV switchgear should be adequately sized and have the necessary protection circuitry equipment to safely interrupt any/all "bolted fault" conditions on the load side.

If the LV equipment cannot do so safely, it is either undersized or faulty and either way should be repaired, tested, and/or replaced as soon as possible.

The upstream MV/HV protection in any electrical circuit should never trip unless the LV protection fails to clear a fault within the acceptable circuit protection time limit.

Allowing the upstream protection to clear a fault will cause great difficulty in determining the location of the fault and will create very unsafe operating conditions not only for the equipment but also for anyone in the immediate vicinity.

Yes, i am fully agree with SHOCKHISCAN:

In case of earth fault in the secondary winding of a the 6.6 kV/ 400V transformer it is better to trip the 400 V ACB first through stand by earth fault protection sensing earth fault current from the CT in the transformer neutral circuit. The 6.6 kV circuit breaker should then be tripped after a time delay.

However for overcurrent or earth fault on 400V side ( incoming bus and outgoing feeders) it may not be necessary to trip the high voltage circuit breaker as the fault will be cleared by the incoming or outgoing 400V ACB.

As per the fundamentals of protection system, faulty feeder should be isolated first to ensure uninterrupted power supply to the remaining consumers fed from the healthy feeders.

In case, the faulty 400 V feeder fails to trip due to any reason, then the respective incoming feeder should trip. If this also fails to trip, then the upstream 6.6 kV feeder should trip. This is achieved through proper protection coordination.

However, automatic tripping of the upstream feeder from downstream feeder and vice versa is possible through shunt trip and suitable interlocking scheme, if required.