Opening LV vs MV Breakers

[lyla1711]

Looking to get consensus here. I have an application where we can either open a 13.2kV vac breaker (feeding a 2000kVA transformer) or a 3000A 480V unit substation breaker (fed by said transformer). There are about 1200A worth of load on the 480V side. Both breakers can be opened remotely. Both breakers are relatively new and fully commissioned.

Really what I am wondering is this: all other things being equal, is it more safe to open a medium voltage breaker or a low voltage breaker?

 

[RRaghunath]

Energising the transformer repeatedly is not a good idea and can harm the transformer life.
I would open the LV breaker when the intent is to remove the connected LV load.

 

[dpc]

Not sure about safety, but agree that opening the low side is easier on the transformer by reducing the number of re-energizations.

 

[xnuke]

Were you asking about equipment safety or personnel safety? Arc flash incident energies might be very different on each side of the transformer.

xnuke
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[dpc]

xnuke: Since both breakers can be remotely operated, the incident energy should not be a big factor - at least to me. But you're right - I'd expect lower incident energy on the primary side.

 

[xnuke]

Ah, missed that in the OP.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[davidbeach]

May not matter here; but if there is any other source on the 480V side it must be opened first unless there's differential protection on the transformer. A Dy transformer that doesn't have differential can't be protected if energized from the 'y' side, and even differential won't detect a single phase-ground fault on the 'D' side. Like I said, it might not matter here, but you have to consider sources and possible fault conditions when determining the order to open or close devices.

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