Hi, I'm new to this forum. I'm an electrical engineer student, i'm currently trying to size a transformers bank to feed the intrinsic 480v loads of a MPU Turbogenerator.

The following loads are connected into the MCC's 480v Bus bar.

Indoor Motor 1/3 HP, 460VAC, single phase, 1.1 A FLA

Outdoor Motor 1/5 HP, 460VAC, single phase, 1.4 A FLA

Compressor 460VAC, 3- phase, 39 LRA and RLA 5.5

1. I would normally use the apparent power equation S = sqrt(3) * VL * I , but i also read that with motors you need to include motors efficiency and power factor with the following:

S = (hp * 0.7457) / (P.F * EFF)

What's the most accurate way to do it? It's for my thesis.

2. How does the VFD affects the load calculation?

3. To size the bank should i add up the kVA and divide them by 3? And how should i do the voltage drop at secondary for each single phase transformer?

I know maybe i'm asking for a lot, i was supossed to size a 3-ph transformer first but they told me it needed to be a 3T bank and i'm confused on how to proceed.

The following loads are connected into the MCC's 480v Bus bar.

**Pre/post lubrication Motor/pump:**2 hp, 460vac, 60hz, 1750 rpm, 2.9 A, p.f 0.8**Enclosure vent fan #1 Motor**: 15 hp, 460vac, 60hz, 6.7 A, p.f 0.85**Oil cooler vent fan #1 Motor**: 5hp, 460vac, 6.7A. 79%**Start Motor :**Duty: 15 minutes inverse service 1760 RPM, 231 A. 0-150 hp, 0-460 vac, 0-4000 RPM.**VFD, Start Motor speed control:**50/60 hz, 0-150 hp, 0-460 vac, 0-4000 rpm**PCR Air conditioner:**Indoor Motor 1/3 HP, 460VAC, single phase, 1.1 A FLA

Outdoor Motor 1/5 HP, 460VAC, single phase, 1.4 A FLA

Compressor 460VAC, 3- phase, 39 LRA and RLA 5.5

1. I would normally use the apparent power equation S = sqrt(3) * VL * I , but i also read that with motors you need to include motors efficiency and power factor with the following:

S = (hp * 0.7457) / (P.F * EFF)

What's the most accurate way to do it? It's for my thesis.

2. How does the VFD affects the load calculation?

3. To size the bank should i add up the kVA and divide them by 3? And how should i do the voltage drop at secondary for each single phase transformer?

I know maybe i'm asking for a lot, i was supossed to size a 3-ph transformer first but they told me it needed to be a 3T bank and i'm confused on how to proceed.

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