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Help me understand how ANSI 47 relay works

Help me understand how ANSI 47 relay works

Help me understand how ANSI 47 relay works

One of the relay on our main circuit breaker is a GE#12ICR53A1A, Ansi#47, Phase Sequence and UnderVoltage Relay.
I've read the manual but still not sure of how it works. This is from the manual:

The Type ICR relays are used to protect AC machines from undervoltage and when
starting from open phase or reverse phase sequence. They will function to stop the
machine if the voltage across the relay terminals falls below a predetermined
value. Usually these relays will not disconnect a running motor if one phase of
the supply is open-circuited because the motor will supply three-phase potential to
the relay even with one phase disconnected from the source. The Type ICR relay
are also used for automatic throw over schemes where it is desired to check the
presence of three-phase voltage of correct phase sequence.

The 47 relay is on 4.16KV MCB that feeds a line up of 4.16KV feeder breakers, that in turn provide cables underground to building transformers. The original purpose of this relay (I am told) was to protect the motors on site from phase loss, and/or, reverse phase rotation. There is a time delay time on the relay set to 3 seconds.

Phase Sequence? Does this phase rotation, in the sense that if I presently have clockwise rotation (ABC), and do to some external mistake the switchgear was supplied with counterclockwise rotation (ACB) the relay would open the MCB? Does the 3 second delay engage on this function. 3 seconds of rotating motors in the opposite direction could do a lot of damage.

Undervoltage Relay? Is this the 'phase lost' part of the relay? I can understand the 3 second timer being here.

Total Loss of Power? All the protective relays are supplied from batteries. So if we have a utility outage, loss all three phases simultaneously, is the 47 relay going to trip open the MCB? I would prefer that it doesn't, as then we could automatically recover once power was restored without suiting up an electrician to close the MCB, but not sure if that is possible. Does the 47 relay take losing all three phases the same as losing one phase?

Any advice you can provide is appreciated.

RE: Help me understand how ANSI 47 relay works

Can you post a schematic of how the relay is wired into the close/trip circuits? That will explain exactly how the ICR53A is being used. The left contact would be used to block starting of the motor and the right contact would be used to trip the running motor. If the left contact is in your motor start circuit, breaker close circuit, it would block the motor from starting if you have two phases swapped or if you have a loss of voltage on one or more phases. The left contact will only close once you have balanced three phase voltage on the bus. On undervoltage, after a time delay, the right contact would close to trip the motor offline.

RE: Help me understand how ANSI 47 relay works

The relay is on a 4.16KV switchgear line up, on the main breaker. The branch breakers all supply feeders to building transformers. There are no motors at 4.16KV. The relay is to protect the entire plant, from phase loss or reverse phase, for all the 480V motors.

1. Are you saying the time delay is only associated with the unbalance (phase loss) portion of this relay.

2. How would this relay react to a 3ph loss of utility power. Would it basically ignore it, as there is no unbalance when all phases go to zero, or would it trip open the breaker.

RE: Help me understand how ANSI 47 relay works

Loss of potential on all three phases will allow the disk to roll to close the right contact. If this is in the trip circuit of the breaker, then the breaker will open.

Note that you can set any two of three parameters with this relay: Left contact close (minimum pickup voltage to allow operation), right contact close (maximum voltage that will trip) and time delay from normal voltage to closing the right contacts on zero volts.

three-phase voltage of proper sequence and magnitude turns the disk to close the left contact, making it the permissive for motor start, if used. Loss of a single phase will allow the disk to slowly roll to close the right contacts to trip. Complete loss of potential will trip relatively fast.

old field guy

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