125V DC Battery Isolator - Shunt Trip

[NickParker]

We have 125V DC Battery system for supplying control voltage to Switchgears. There is a battery Isolator box with MCCB for it. The Client has specified both the under voltage relays and the Shunt trip coil for it.

In general, which is preferred, UV coils or Shunt trip coils for this battery Isolator? If shunt trip coil is used, is it wired to Battery charger or to the battery bank?

 

[waross]

That would depend on the client's wishes.
If he is specifying a device, he must have a thought in mind as to how it is to operate.
However, be prepared with a suggestion in the event that he has cut and pasted a spec without understanding it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

The under voltage relay measures the battery voltage and then energizes the shunt trip when the batteries are at a maximum state of discharge to protect them from excessive discharge damage.

You could use an under-voltage trip coil instead of a shunt trip coil, but then it's a constant load the batteries have to supply which must be taken into account when sizing the battery bank.

 

[che12345]

Dear Mr. NickParker ,

Q. " We have 125V DC Battery system for supplying control voltage to Switchgears. There is a battery Isolator box with MCCB for it. The Client has specified both the under voltage relays and the Shunt trip coil for it....".
A1. There are differences in function and operation:
a) An [under-voltage release] MUST be (energized) in order to enable to close the switching device. The release MUST be [energized continuously] to maintain the switching device in (close position). It trips off the switching device when the release voltage drops to a certain value per the Standards. The release is designed for (continuous energization).
b) A [shunt release] MUST be in (de-energized) state in order to be able to close the switching device. The release MUST be [de-energized continuously] to maintain the switching device in (close position). When the switching device is (in closed state), the switching device [opens] when the shunt release is energized. The voltage must be of certain value (per Standard) to operate the release. The release is usually NOT designed for [continuous energization].
c) In most cases, irrespective of whether the switching device is an ACB, MCCB or MCB etc, they usually having provision room for either (one not two) under-voltage or shunt. Some ACB with acceptation, may have room for two.
d) In general practical applications, only [one NOT two] is required. Which type is dependent on the design/application or preference/practice of the plant.
A2. Release operation voltage source:
a) For [under-voltage release] the operation voltage source MUST be taken [before] the switching device, at the incoming for example.
b) For [shunt release] the operation voltage source MAY be taken [before or after] the switching device. Attention: The operation voltage source MUST be taken [after] the switching device if the release is NOT fitted (internally) with a NO contact/switch in series with the release, preventing it from continuous energized.
Che Kuan Yau (Singapore)