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Three phase heater wiring and load calculations

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Posted by MaheshChhatbar (My Page) on
Sun, Dec 23, 12 at 3:52

I have a heater unit of 18 KW
It is a Three Phase unit in which I have connected 4 x 1.5 KW heater across each Phase to Neutral.
thus having 3 x 4 x 1.5 KW = 18 KW Total.
It draws appx 24 amps per phase and appx 1 amp in neutral due to little imbalance in heater.
The above are connected as Star or WYE. We have appx 240 V across Phase to neutral.

Not I intend to increase my heating to appx 27 KW.
I am to place an order for 1.5 heaters rated at 415 VAC
I will be connected the heaters as Delta.
That is 6 heaters is connected across two phases.
Thus I will be connecting 3 x 6 x 1.5 KW Heaters = Total 27 KW.
What I wish to know is what will be the ampears drawn from each phase of the supply.
I am confused.
Please help.

Thanks & Best Regards

Mahesh

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RE: Three phase heater wiring and load calculations

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Very confusing. there is no neutrol in 3 phase. Ohms law.
do the math. Total amps or amps per element ?

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RE: Three phase heater wiring and load calculations

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I was curious as to how to solve this problem so I did a little research. I think my answer is correct.

Changing the configuration from wye to delta increases the voltage across each heater by a factor of 1.73 (square root of 3). The heater voltage becomes:

240V * 1.73 = 416V

If you want to dissipate 27KW of total power then divide by the voltage to get the current through the heaters:

27000W/416V = 64.9amps

To get the line current through each heater divide the total by 3:

64.9amps/3 = 21.6

The currents from the supply is the summation of the currents in the heaters. The line currents are out of phase by 120 degrees so you need to multiple by 1.73:

21.6amps * 1.73 = 37.5amps

Below is a link for a wye and delta calculator. You can plug in any two numbers and calculate the others.

Merry Christmas

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RE: Three phase heater wiring and load calculations

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Y-connected 3-phase does have a neutral. Delta connected does not.

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