breaker tripping

[jhochb]

Good morning all
I’m doing a festival at a Miami sound stage and I have an issue with one of the three disconnects. Please read the post before responding.
The room
There is a 1200A, 480V serves feeding 3-250A, 480V Breakers.
The 250A breakers go to disconnects in the room.
I am told this is a WYE setup without the neutral.
Out of these cans I’m feeding 480V to the Delta input of the 480/ 208V transformers, WYE output.
The issue
One of the 3, 250A breakers trip when it has a transformer connected.
This is the second gig in this room and the house electrician told me they replaced the breaker. The issue persists.
What I’ve done
On the first gig I tied in my tails and checked power at all 3 cans.
All good
All connections are done cold, no power.
I had a 112KVA & 2 - 75KVA transformers. We later swapped the 112KVA for a 150KVA.
I powered down and connected the transformers, powered up with no load.
Cans , A & C were fine. Can B tripped the 250A, 480V breaker.
All 4 transformers worked fine on cans A & C but tripped can B
Cans A & C ran the week just fine, we didn’t use can B
This gig
It happened again. This time the transformers are not on wheels. so it's harder to swap them.
This time the house provided the tails. I metered power and connected my 3 150KVA transformers.
B tripped.
The house called in an electrician, the can metered OK. The electrician suggested the phasing was off. ???????
Any real thoughts?
I don’t have a MEGA or. a HIPOT meter but I would like to check the lines back to the breaker. I used my Fluke 179, no help there. With what I have here I can’t go further.
*
Help me Obi Wan.

 

[FMEng]

Get your hands on a clamp ammeter with instantaneous peak hold. Fluke calls that inrush measurement. With that, you'll be able measure what is happening in the instant before the breaker opens and prove where the fault lies. My guess is it is still a faulty breaker. Either they changed the wrong one, or there's a defective batch on the loose.

If there were a fault beyond the disconnect, with 250 Amps flying around, it seems like there would be some hint like noise, light, or smoke.

 

[STEVETERRY]

Good morning all
I’m doing a festival at a Miami sound stage and I have an issue with one of the three disconnects. Please read the post before responding.
The room
There is a 1200A, 480V serves feeding 3-250A, 480V Breakers.
The 250A breakers go to disconnects in the room.
I am told this is a WYE setup without the neutral.
Out of these cans I’m feeding 480V to the Delta input of the 480/ 208V transformers, WYE output.
The issue
One of the 3, 250A breakers trip when it has a transformer connected.
This is the second gig in this room and the house electrician told me they replaced the breaker. The issue persists.
What I’ve done
On the first gig I tied in my tails and checked power at all 3 cans.
All good
All connections are done cold, no power.
I had a 112KVA & 2 - 75KVA transformers. We later swapped the 112KVA for a 150KVA.
I powered down and connected the transformers, powered up with no load.
Cans , A & C were fine. Can B tripped the 250A, 480V breaker.
All 4 transformers worked fine on cans A & C but tripped can B
Cans A & C ran the week just fine, we didn’t use can B
This gig
It happened again. This time the transformers are not on wheels. so it's harder to swap them.
This time the house provided the tails. I metered power and connected my 3 150KVA transformers.
B tripped.
The house called in an electrician, the can metered OK. The electrician suggested the phasing was off. ???????
Any real thoughts?
I don’t have a MEGA or. a HIPOT meter but I would like to check the lines back to the breaker. I used my Fluke 179, no help there. With what I have here I can’t go further.
*
Help me Obi Wan.

Does the 250A breaker have adjustable trip parameters on its face? If so, it may be that the "short time pickup" parameter is set too fast for the coil energization inrush current of the transformer. And that might be the default setting as shipped from the manufacturer, which would explain why two new breakers are tripping. If you can provide the manufacturer and model of the 250A breaker, we may be able to help further.

ST

 

[jhochb]

Get your hands on a clamp ammeter with instantaneous peak hold. Fluke calls that inrush measurement. With that, you'll be able measure what is happening in the instant before the breaker opens and prove where the fault lies. My guess is it is still a faulty breaker. Either they changed the wrong one, or there's a defective batch on the loose.

If there were a fault beyond the disconnect, with 250 Amps flying around, it seems like there would be some hint like noise, light, or smoke.

Good Morning
I'm looking into better meters, at the moment that's not in the budget.
no noise, no smoke & no sparks.
I thought of inrush, but 2 breakers in a row?

 

[jhochb]

Does the 250A breaker have adjustable trip parameters on its face? If so, it may be that the "short time pickup" parameter is set too fast for the coil energization inrush current of the transformer. And that might be the default setting as shipped from the manufacturer, which would explain why two new breakers are tripping. If you can provide the manufacturer and model of the 250A breaker, we may be able to help further.

ST

Good Morning Terry

it's a GE breaker. most of the face is covered so I can't tell if there is an adjustment. there is a red button, flush, near the lower right of the handle.
today is the last show & tomorrow is load out. I won't be back in this room for more than half a year.
maybe by that time I can get the meters I need to find out what's up

thank you all for your input and I WILL repost next time I'm here.