11KV Switchgear Design

With the single UV relay if you switch on the bus coupler there will be much problem provided your incomers are designed to work parallel. That means even if for a very small interval of time both the feeders may be simultaneously ON and should not cause any damage due to the delay in operation of the relay contacts . If that is not the case then you should go for double relay operation for switching of bus coupler.

Please note that two incomers are not designed to work parallel and so no synchronizing check relay is considered. Two of Three circuit breakers are closed at the same time.

This is called auto change over scheme.

I have done many such schemes for reputed installations in india.

It is enough to have two Under voltage relays on incoming sides of 11 kV VCB.

But suitable logic circuitary to be developed for tripping and closing and interlock two incomers and one buscoupler.You can use some timers and auxiliary relays to achieve this or a simple PLC will serve the purpose.For further help please send email.

I am sorry, but I think you intended to say that the bus coupler is normally open and the two incoming feeders normally closed, is it ?

In automatic transfer, it is important to check if the transfer will occur by connecting the other feeder to a dead bus.

Therefore, your client probably has the fear that the bus is not dead during the transfer interval. This may be because he has any synchronous machine connected to the bus or the system foresees an UPS connected to the secondary of a voltage transformer.

In this case, it is advisable to have voltage detector relays in each bus.

Please note that you do not actually need to use undervoltage relays, because the purpose of the detector is to check if the bus is dead or not.

Regards

Yes, the bus coupler is normally open and the two incoming feeders are normally closed. But there is not any motor directly to switchgear.

I think these feeders supply power to 11 kV transformers.Once 11 kv supply fails,the Incoming LT supply to LT board through ACB can be made to trip so that back feeding from UPS through transformer will not take place and it will be definetely dead bus.

One has to gothrough complete scheme and philosphy of operation of VCBs and ACBs before we conclude the provision of undervoltage/ no voltage relays and no of relays etc.

I had suggested for a simple system.

Dear Friends,

11KV incoming feeders will be supplied from two synchronized sources by client.

I had sent the sketch giving brief circuit.Please confirm receipt and give your feedback.

Many Thanks

I have received your sketch.

Two stage UV schematic is used as reacceleration scheme. Generally reacceleration schemes are used for individual motors depending upon their importance. normally it works like this:

If a bus voltage dip causes all motors to drop and the full voltage comes back within certain short time (stage-I) some of the essential motors should start automatically. If the delay is more (stage-II) then only some of the motors to start automatically. for a longer delay all motors to drop completely and restart requires complete reset.

Kamalakar

could someone show me how to design a basic switchgear system

Second relay client is asking for to ensure no voltage on the dead bus. Capacitive voltage may exist on the dead bus. To sence no voltage another undervoltage having setting 0-10% is required.