How current unbalance will effect on a 3 phase transformer winding?

[vinod]

:?One of our 45Kva, 480/480-277v utility transformers is feeding to a 3phase power panel through a 3 pole main breaker. One of the poles on this breaker is damaged and no continuity between line and load side. But we badly need to energize this panel even with 2 phases.
My questions are,
1. Can I keep this transformer energized with unbalanced load?
2.Will current unbalance between phases damage the transformer winding? If yes please explain.:?

 

[jghrist]

:?One of our 45Kva, 480/480-277v utility transformers is feeding to a 3phase power panel through a 3 pole main breaker. One of the poles on this breaker is damaged and no continuity between line and load side. But we badly need to energize this panel even with 2 phases.
My questions are,
1. Can I keep this transformer energized with unbalanced load?
2.Will current unbalance between phases damage the transformer winding? If yes please explain.:?

There's no problem with the transformer. All it cares about is not overloading any phase. One possible problem is unbalanced loading through the transformer impedance causing unbalanced voltage because of low voltage drop on one phase. Unbalanced voltages can cause problem with 3? motors.

 

[templdl]

You must assure that each of the 2 remaining phase does not exceed 1/3 of the rated KVA of the transformer. If it is a 45kva transformer each of the remaining phases must not exceed 15KVA each.
But try this, exercise the breaker by turning it on and off numerous times. If the suspect contacts in the phase that is open are not severely damaged it may be possible to get those contacts to work again. Breaker contacts actually rub together when they close which is why breakers should be exercised periodically. But be aware that the contacts of the suspect phase may get warm because there may be contact resistance.

 

[vinod]

But try this, exercise the breaker by turning it on and off numerous times. If the suspect contacts in the phase that is open are not severely damaged it may be possible to get those contacts to work again. Breaker contacts actually rub together when they close which is why breakers should be exercised periodically. But be aware that the contacts of the suspect phase may get warm because there may be contact resistance.

Thanks for your advise. But this was happened due to improper tightness :rant:
See attached snap of damaged breaker
View attachment untitled.bmp

 

[templdl]

Can't see your picture.

Often times a loose line side terminal will cause heating which will be transfered to the stationary contact in the breaker to the moving contact heating the spring that holds the moving contact closed. The spring's tension is compomised weakening the spring and no longer hold the moving contact tightly agaist the stationary contact and it gets worse from there.

As such exercising the breaker is of no use.