Hello,

Thank you in advance for all the tips and answers. Recently we moved to a warehouse and we just paid over $300 bill for the one month from Consumers Energy, which I believe is caused by the transformer that we don't really use. We have some lights and computer only in the warehouse, no machinery. On the bill it stated we used:

2261 kWh - this from using about 25 fluorescent lights (each containing 6x32W tube lights) and 6 computer stations, that's it.

The building has a power line from Consumers Energy at 480V, which was used for welding by previous occupant. The line is connected to a large panel where there is only one breaker one at this moment - for the step down transformer to 240V, which feeds smaller panel with all small (120V) electrical outlets and ceiling lights.

My questions are:

1. How to calculate the power consumption of that transformer when it's in idle (everything in the warehouse is shut off, but the transformer is on and buzzing)?

We have given:

11.3 A

measured by electrician today at the cables that run from large 480V breaker in large panel to the transformer (three cables are there, 4A, 3.3A, 4A, totaling 11.3A)

480V which is the current going to the transformer

Some source also mention Power Factor, do you know if it applies here and if so at what value? I just assumed is is value of 1, so kVa=kW

From what I found this suppose to be:

11.3A x 480V x 1.73 (square root of 3) = 9383.52 VA = 9.38 kVA(kW)

Is it correct?

If so, continuing, what is our power consumption when all the lights and devices are on? Measured amps as well today by electrician (14A, 10A, 9A, totaling 33A)

33A x 480V x 1.73 (square root of 3) = 27434 VA = 27.43 kVA(kW)

Now, if this is correct, our facility runs 40 hours a week with all the lights and computers on and 128 hours a week with the lights off and transformer at idle. That will give us:

40h x 27.43kW = 1097.2 kWh

128h x 9.38kW = 1200.64 kWh

Total 2297.84 kWh per week, assuming 4 weeks per month = 2297.84 x 4 = 9191.36 kWh which is not equal the consumers energy reading (2261 kWh actual) and I am sure this calculation is incorrect because the bill would be $1011.45 at rate $0.11/kWh.

Where is an error here?

Thank you in advance for all the tips and answers. Recently we moved to a warehouse and we just paid over $300 bill for the one month from Consumers Energy, which I believe is caused by the transformer that we don't really use. We have some lights and computer only in the warehouse, no machinery. On the bill it stated we used:

2261 kWh - this from using about 25 fluorescent lights (each containing 6x32W tube lights) and 6 computer stations, that's it.

The building has a power line from Consumers Energy at 480V, which was used for welding by previous occupant. The line is connected to a large panel where there is only one breaker one at this moment - for the step down transformer to 240V, which feeds smaller panel with all small (120V) electrical outlets and ceiling lights.

My questions are:

1. How to calculate the power consumption of that transformer when it's in idle (everything in the warehouse is shut off, but the transformer is on and buzzing)?

We have given:

11.3 A

measured by electrician today at the cables that run from large 480V breaker in large panel to the transformer (three cables are there, 4A, 3.3A, 4A, totaling 11.3A)

480V which is the current going to the transformer

Some source also mention Power Factor, do you know if it applies here and if so at what value? I just assumed is is value of 1, so kVa=kW

From what I found this suppose to be:

11.3A x 480V x 1.73 (square root of 3) = 9383.52 VA = 9.38 kVA(kW)

Is it correct?

If so, continuing, what is our power consumption when all the lights and devices are on? Measured amps as well today by electrician (14A, 10A, 9A, totaling 33A)

33A x 480V x 1.73 (square root of 3) = 27434 VA = 27.43 kVA(kW)

Now, if this is correct, our facility runs 40 hours a week with all the lights and computers on and 128 hours a week with the lights off and transformer at idle. That will give us:

40h x 27.43kW = 1097.2 kWh

128h x 9.38kW = 1200.64 kWh

Total 2297.84 kWh per week, assuming 4 weeks per month = 2297.84 x 4 = 9191.36 kWh which is not equal the consumers energy reading (2261 kWh actual) and I am sure this calculation is incorrect because the bill would be $1011.45 at rate $0.11/kWh.

Where is an error here?

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