motor calculation

[RonR]

I need to run a 40 hp and a 30 hp motor at the same time.

I will be feeding both motors from a step up xfmr(208/120v 3 phase to 480 v 3 phase)
to a panel that has a 175 amp main breaker. What is the required Kw rating of the step up xfmr??


the existing step up xfmr is 112.5 Kw and it is running a 20 hp and a 30 hp at
the same time.

 

[petersonra]

I need to run a 40 hp and a 30 hp motor at the same time.

I will be feeding both motors from a step up xfmr(208/120v 3 phase to 480 v 3 phase)
to a panel that has a 175 amp main breaker. What is the required Kw rating of the step up xfmr??


the existing step up xfmr is 112.5 Kw and it is running a 20 hp and a 30 hp at
the same time.

You are around 75 kVA with both motors running. 112.5 is probably adequate.

 

[Dennis Alwon]

So in the end you have a 112.5kw trany that will run a 40 hp, 2- 30 hp and a 20 hp motor? I think you will be okay

 

[RonR]

I will be removing the 20 hp and installing a 40 hp so there will
be a 40 & a 30 at the same time.


p.s. is the 175 amp main breaker in the panel still ok??

 

[Dennis Alwon]

The breaker depending on the wire size to the transformer could be fine. I expect that you have a panel with a breaker on the load side of the trany?

 

[RonR]

So in the end you have a 112.5kw trany that will run a 40 hp, 2- 30 hp and a 20 hp motor? I think you will be okay

sorry, i forgot something.

actually I will be running 2- 40 hp or 1- 40 hp & 1- 30 hp so
it will end up at 80 or 70 hp at the same time.

is the 175 amp main breaker ok??

 

[RonR]

The breaker depending on the wire size to the transformer could be fine. I expect that you have a panel with a breaker on the load side of the trany?

the main breaker is 175 amp, the individual breakers to the 20 & 30 hp are
70 amp. should the breakers to the 40 hp be larger than 70 amp??

 

[ptonsparky]

the main breaker is 175 amp, the individual breakers to the 20 & 30 hp are
70 amp. should the breakers to the 40 hp be larger than 70 amp??

Most likely.