Closing 480v Tie Circuit Breaker with no Sync check 1

[Mila2015]

I have a situation where a client has a 480v, GE WPH Tie circuit breaker that needs to be manually closed. I didn't see sync checking in it's closing circuit, so I know there is no automatic voltage and Phase angle check, but the 500KV feeding network should be the same, and both units should have the same set-up (XFMRs, SWGRs....etc). Can breaker be closed with buses energized? I would assume we would be to verify XFMR taps are the same, and voltages are close...anything else?

 

[Mbrooke]

Unless you check, there is no way to know. To many variables at play, especially in regards to what is in between the 500kv system and 480 volt system.

 

[Palletjack]

I would simply check the voltages on each side of the breaker before any energized tie is attempted.
If you read 0 volts same phase to same phase, and 480 on the other phases, your good to go.

 

[RRaghunath]

Mila2015, Tie breaker can be closed without Synch check provided the tie breaker at the upstream switchboard (that feeds the two transformers connected to the 480V switchboard) is closed.
I have seen such schemes which interlock the low side tie breaker with that upstream (the low side tie cannot be closed unless the upstream tie is closed).

 

[unclebob]

Your 480 V switchgear must be able to withstand twice the interrupting current, coming from the 2 transformers.

Example:

Your switchgear is fed by 2 transformers: 2000 kVA, secondary at 480 V and 5% impedance.
Each transformer have an FLA of 2400 A approx. In a 3-phase bolted fault situation, each will provide 48000 A in a 480 V fault (1/5% =20 times the FLA).
With the Tie breaker open, each side of the switchgear need a 50 kA interrupting current capacity. If the Tie is closed, with both Main breaker closed, your 480 V
gear now has to be able to withstand 96 kA. This is an issue if your system is less than 96 kA.

What is the power of your transformers?
In any case, there is a serious Arc Flash hazard operating these breakers.

 

[stevenal]

Use Palletjack's method to check phasing prior to the first closure and after wiring is disturbed. Sync check isn't needed when there is only one source, but a one time phasing check is certainly needed.