Transformer sizing 3phase 120/208wye - 480 delta

[Fordean]

I have a project. The new power washer is 60 HP @ 480 Volts @ 48 Amps 3phase
I have to use a stock type transformer. For the one which I spec'd is 14 week out to 10 weeks
I would like to try a 45kva I used a 50 in spec. Only 2 in stock are the 45 KVA and a 75 KVA

I planned on 150 amp tapped from 400 amp main. (1/0 thhn thinking ALum maybe that would be 2/0)

Can someone check my calc.

I calculated the Incoming

208volt 3 phase to 39.9 KW.
480volt 48a 3phase 19 kw

 

[augie47]

Calculations appear to be way off. 19kw @ 480v3 phase is 22 amps. 48amp would be 40kw,
The 45kva would possibly be "light" for a motor load.

 

[Dsg319]

I would suggest sizing transformer at a minimum of 125% of FLC out of NEC.

I don’t know much about sizing trannys for motor loads but I know during the locked rotor current of the start up of the motor if not sized large enough you could have extreme voltage drop resulting in a motor not starting.

 

[David Castor]

I'd recommend double checking the motor data. A 60 hp, 460 V 3-phase motor has an NEC FLA (430.250) of 77 A. 1 kVA per hp is generally a good rough approximation. So 60 hp would be about 60 kVA. This is 72 A at 480 V.

Something seems off on the motor data.

 

[Fordean]

I'd recommend double checking the motor data. A 60 hp, 460 V 3-phase motor has an NEC FLA (430.250) of 77 A. 1 kVA per hp is generally a good rough approximation. So 60 hp would be about 60 kVA. This is 72 A at 480 V.

Something seems off on the motor data.

I read the label on the machine's requirements.

 

[infinity]

It's 48.2 HP and 48 amps which is about right.

 

[Fordean]

It's 48.2 HP and 48 amps which is about right.

Thanks, I got motor HP confused with another job.

 

[Fordean]

I'd recommend double checking the motor data. A 60 hp, 460 V 3-phase motor has an NEC FLA (430.250) of 77 A. 1 kVA per hp is generally a good rough approximation. So 60 hp would be about 60 kVA. This is 72 A at 480 V.

Something seems off on the motor data.

You were right. Its not 60 its 48.8 HP. Got confused with other job. Picture is below.

 

[augie47]

side note: I looked at the operating instructions and spec sheet and, it may be generic, but the install instructions call for GFCI protection.
Something to think about

 

[kwired]

I have a project. The new power washer is 60 HP @ 480 Volts @ 48 Amps 3phase
I have to use a stock type transformer. For the one which I spec'd is 14 week out to 10 weeks
I would like to try a 45kva I used a 50 in spec. Only 2 in stock are the 45 KVA and a 75 KVA

I planned on 150 amp tapped from 400 amp main. (1/0 thhn thinking ALum maybe that would be 2/0)

Can someone check my calc.

I calculated the Incoming

208volt 3 phase to 39.9 KW.
480volt 48a 3phase 19 kw

KVA should be same both sides of the transformer. Rated amps is what will change. A 45KVA unit should be rated 125 amps on low volts side and 54 on the high volts side. That should be too small for a 60 HP motor, but I see we concluded this is only a 48 HP motor - getting close but possibly still a little undersized.

 

[topgone]

KVA should be same both sides of the transformer. Rated amps is what will change. A 45KVA unit should be rated 125 amps on low volts side and 54 on the high volts side. That should be too small for a 60 HP motor, but I see we concluded this is only a 48 HP motor - getting close but possibly still a little undersized.

Same ideas here. I size transformers 140% of the expected load +, + any other future loads!

 

[David Castor]

I think a 45 kVA transformer would be too small.

 

[zbang]

I looked at the operating instructions and spec sheet and, it may be generic, but the install instructions call for GFCI protection.

Most likely, they sell a lot of consumer machines (although mine came with a GFCI on the cord).