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# Electrical Math Question!

#1
09-20-15, 07:08 AM
Member
Join Date: Dec 2014
Posts: 12
Electrical Math Question!

Thanks to those who gave advice on a previous thread, now hopefully this is simple!

I'm trying to calculate the electrical cost of running some equipment but struggling to get all the conversions correct.

Here are the variables..

600v power going to a 150kva transformer with 120/208 output. The transformer is a WYE line-neutral.

What I am trying to calculate is the KWh (assuming 100% consumption for ease of math)

I found something online that gave me 144kwh but not sure if i entered all the variables correctly? Is that close?

Thanks

#2
09-20-15, 07:26 AM
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,285
You cannot calculate the KWh because you do not have the load of the equipment. This should be in watts or KVA

The transformer will have some no load losses, but they will be very small.

Are you trying to find the cost of running a no load transformer?

#3
09-20-15, 07:30 AM
Member
Join Date: Dec 2014
Posts: 12
The background behind this is we are trying to guestimate the cost of usage by production companies that will hook up their lights etc to the dedicated transformer. Their usage will fluctuate but we wanted a 'worst case scenario' so we don't lose money on the deal. With roughly 400A (i believe) available, if we assumed they averaged 300A usage, how would that calculate out?

#4
09-20-15, 07:50 AM
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,285
That is going to be very hard to guestimate because of there are so many variables. How much equipment will a tenant have? Are they line to line loads only or is there loads to neutral? Does this include lighting and/or HVAC? How long will the equipment be running, 24/7 or only 8 hrs per day? What about office loads?

I would look at installing a sub meter on the 600 volt feeder. Emon Dmon is a good one out there. then the tenant will pay for the power they use.

To answer your math question I used this calculator to figure KW: Amps to Kilowatts (kW) conversion calculator and used the following numbers:
AC 3 phase
300A
line to line volts
208volts
.90 power factor
97.27 KW

You then have to put in time for KWh:
97 KW x 8 hours per day = 776 KWh
776 x .15 (cost per KWh) = \$116.4 per day

Be sure to check your utility for the cost per KWh in your area. Also commercial rates are different then residential.

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