Square d mini power zone

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Jab161

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Installed 2 22.5kva mpz 480v primary the unit was powered up and left with no load for a month. When we returned the xfmr was very hot! Could only touch it for like 2 seconds. I put a clamp on the 480v coming in and there was a 5 to 7 amp load on the 3 phases.
Again there is no load on the secondary. Everything is grounded/bonded properly
the incoming voltage is a little high around 283v ph to gr and 495 ph to ph. Any thoughts
 
Use a thermometer not your hand.
Being able to contact for 2 secs may not be unusual. Most of those MPZ transformers use the skin of the enclosure as the heat exchanger, so they are extremely hot to the touch.
 
jim dungar said:
Use a thermometer not your hand.
Being able to contact for 2 secs may not be unusual. Most of those MPZ transformers use the skin of the enclosure as the heat exchanger, so they are extremely hot to the touch.
Click to expand...

Agreed, my concern is the heat with no load on the secondary. And the load being drawn by the xfmr
 
Jab161 said:
Agreed, my concern is the heat with no load on the secondary. And the load being drawn by the xfmr
Click to expand...

I am saying that 2sec is a fairly long time to be able to hold your hand there.
Come back with the actual temperature and the transformer part number.

According to Schneider Electric's FAQ website.
What is the maximum temperature that a Mini Power-Zone enclosure surface can reach?
The maximum allowable surface temperature rise above ambient for a Mini Power-Zone (MPZ) is a 65degC. With maximum ambient temperature of 40degC, the surface of the MPZ could reach 105degC (221degF.) Remember the 24 hour average ambient should not exceed 30degC (86degF.)
Click to expand...
 
I get this kind of question regarding motors all the time. Several studies on human pain thresholds related to heat peg the hand as becoming painful at a dermis-to-epidermis (skin to below skin) temperature of 44 C (111 F). From a transformer winding insulation standpoint, that's "cool".

By the way, if the transformer is completely unloaded, that 7A of current you saw was all magnetizing current, so the power factor would be really low, as in 0.2 or so. That means that even though you might calculate the VA as over 3 kVA, the actual WATTS would be only about 670. Still, think of a 11 60W light bulbs bunched together.... yeah, it's going to feel warm.
 
Jab161 said:
Installed 2 22.5kva mpz 480v primary the unit was powered up and left with no load for a month. When we returned the xfmr was very hot! Could only touch it for like 2 seconds. I put a clamp on the 480v coming in and there was a 5 to 7 amp load on the 3 phases.
Again there is no load on the secondary. Everything is grounded/bonded properly
the incoming voltage is a little high around 283v ph to gr and 495 ph to ph. Any thoughts
Click to expand...
Hot?? Please define what you mean by hot.
 
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