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Help sizing Xformer

Joined
Jun 9, 2008
Location
Burbank, CA
Guys,

Need to power an induction heater. Unit requires 40 amps of 480 volt, 3 phase.

I have 200 amps of 240 volt 3 phase available.

I guess I need to know the KVA rating of the step up transformer.

Thanks in advance.

Chuck
Burbank, CA
 
40amps at 480 volts is 19KW.

if the duty cycle is low, you can undersize the transformer.

heat goes with the current squared, if you use a 10kw transformer, it would overheat beyond 25% duty cycle.

Its also likely you'll never draw the full 40 amps, it entirely depends on the load and matching the work coil for your task.

Its pretty typical for the amps listed on the nameplate to be 25% more than the unit will ever draw, so that the customer will never have a problem with a breaker tripping. for example, every 4 or 5 ton heat pump i've looked at will state on the nameplate: minimum circuit amperage 40 amps. the max it will ever pull is about 30 amps.

I built an induction heater in my barracks room in the usmc in 2010 btw, so i'm not entirely making this up.
 
Guys,

Need to power an induction heater. Unit requires 40 amps of 480 volt, 3 phase.

I have 200 amps of 240 volt 3 phase available.

I guess I need to know the KVA rating of the step up transformer.

Thanks in advance.

Chuck
Burbank, CA

Heating is easy compared to starting motors as loads, so what that ex-jarhead just said. The basic math JF works. For a change..

:)

Then availability and shipping costs weigh-in.

Too small overheats. Too large is an initialization PITA and wasteful if/as/when idling. You will want disconnects on the INPUT side, IOW.

Your search-for-a-bargain range should be about 20 KVA 'dry type"...fortunately a common rating, indoors., outdoors, NEMA dual use housing.

Copper-wound is better, but any MAJOR maker knows how to do shiney-wood properly, too. They have scant choice, given the costs.

Transformers actually DO have "moving parts" consequently CAN "wear out".

Not only do the laminations move, the wire in the windings is actually squeezed to a tiny, tiny amount of smaller diameter and ever-so-slightly longer length, then reversed, with every cycle over scads and scads of cycles.

Designers expect that, goal for 20-plus years of fatigue-endurance of continuous cycling with rounded-corner or "semi-square" coils, twice that with R.E. Uptegraff's "elliptical" wound bobbins. There are white-papers on all that s**t.

But the bottom line is that most "dry type" used transformers that look OK probably ARE OK as far as low-risk purchases. Few ever ACTUALLY get "worn out" OR "burnt up" and survive into for-sale inventory of any "regular dealer". Smoke trails, polymer stencch, burnt places at terminals, etc? Off they go to recover the metal. Recyclers don't want hassle any more than new OEM want it.

Most used goods are in the market because of business needs changes, alterations, and upgrades. SOME were of low-efficiency designs, but not by MUCH.

Others were surplused off the back of commercial business operating / economic failure, not electrical failure.

If in doubt, check new prices first, THEN scout to see if you can gain for the modestly greater risk.

2CW
 
Thanks for the quick, informative responses.

Most of the transformers out there are Step Down Transformers, I was intending to get one of them but use it as a Step-UP transformer. Will the 20KV recommendation still apply or would I need to double it to 40KW?

Thanks in advance.

Chuck
Burbank, CA
 
Thanks for the quick, informative responses.

Most of the transformers out there are Step Down Transformers, I was intending to get one of them but use it as a Step-UP transformer. Will the 20KV recommendation still apply or would I need to double it to 40KW?

Thanks in advance.

Chuck
Burbank, CA


Most are "reversible". One can "usually" confirm that for a given "family" of transformers off the maker's website with the model number, even if an older model, used.

Same "KVA" either way. You may want to look also at the Amps @ Voltage of each side - it's in the specs.

There is a SLIGHT disadvantage to running a transformer bass-ackwards. It has to do with which windings are closest to the Iron core - "input" or primary being the goal for best efficiency and right on-spec Voltage (ratio). So the Voltages and transfer efficiency are a skosh less-optimal when powered from the intended "secondary".. but your local SOURCE Voltage may not be right at "nominal", anyway.

And "slight" is all it is as far as "direction" goes.

Heating devices won't ordinarily care.

What are they going to do?

"Run HOT?"

"Send you to Veeee Etttttt Naaaaaaaaamm", maybe?

:)

If the Voltage is a bit high - or low - their own controls just cycle them for a very slightly shorter - or longer - ON time to hit and hold a commanded temperature/target.

"BFD", IOW.
 








 
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