Interposing relay. 1

[pala]

We are in the process of introducing a time delay relay to prevent continuous energisation of the trip coil of a 13.8kv breaker under specific circumstnces. The relay coil would have to act under 48v dc but the contact would be a 250vdc one. We would need aninterposing relay. I need to be clear in all factors needed to choose this relay. Any suggestions would be appreciated.

 

[dpc]

I'm not quite clear if you are asking about a suitable time delay relay or just the interposing relay. Since you are tripping a circuit breaker, you could just use a standard lockout relay as an interposing relay, unless you will want to close the breaker remotely.

Otherwise, consider General Electric Type HGA, or if you need a lot of contacts, you could use a General Electric Type HFA.

 

[busbar]

The reason for the wide DC-voltage range spec is not apparent, but in most cases an auxiliary "52a contact" [and possibly anti-pump feature] are furnished on the original assembly to interrupt trip-coil power when the breaker mechanically opens. Such controls must be carefully evaluated as highly reliable for some fierce inductive-DC interruption characteristics.

Be cautious of trip-control modifications that are outside of those OEM furnished. It is very likely the OEM has been through a lengthy learning curve, and it can be most preferable learning from them—as opposed to experiencing a metal-vaporizing maloperation first hand.

 

[pala]

Well, We have decided we would rely on the 52a contact for isolation of the trip coil. The wide voltage range is because the breaker operates on 250Vdc and it is not permitted to have 250V dc at the main control room.

This trip coil is a dedicated one to trip the breaker under accident conditions and we should avoid the breaker from charging again. We are thinking about providing contacts to seal in the motor to avoid charging of a closing spring after a trip. These contacts have to be of a high rating, I realize that this is an issue to be handled with caution I need expert advice on choosing such a Relay or is there any other option.

 

[peterb]

The application you describe is a good example of a situation where a hand-reset lockout relay is usually used. This is a high speed tripping relay which is mechanically held in the trip position until the mechanism is reset by hand (or by an electrical reset coil). A normally closed contact of the relay is wired in the closing circuit of the breaker, so that it cannot be closed without first resetting the lockout.
Examples of these relays would be GE type HEA, Electroswitch type LOR, Alstom type MVAJ - check their websites for details.
The breaker 52a contact is still required in the trip circuit, as it is for any application. This contact is rated to break the high DC current in the trip coil.

 

[SMB1]

please list the conditions which are required to isolate the trip coil of CB by time delay relay.
It is known that the trip coil of CB is always isolated by breker auxiliary contact.