Hi, I have an issue and would like some help.

I have a 3 element heater connected in delta. 4.5KW, 9KW and 9KW. Heaters are powered by 480VAC.

I have measured the following impedance on the heater:

AB: 20.0 Ohms
BC: 27 Ohms
AC: 20.4 Ohms

I also measured line current (current clamp) and got the following readings:

A: 22.3
B: 30.7
C: 22.5.

Could anyone enlighten me as to how I could use these info and calculate the power of this heater assembly? Total power should be 22.5 KW but I cannot come up with the right numbers.

As a last request, could anyone post a link to a website where I could find useful info regarding 3-phase power and related calculations?

Thank you,
EE

 

EE... the measured ph-ph resistances, i.e., 20.0, 27.0, 20.4 don't agree with those calculated from the kW values and voltage you cited.

For example the R related to the 9.0 kW heating element is V^2/(1000 x 9.0) = 25.6 Ohms! If the rated voltage is 460 instead of 480, then the calculated R is 23.5 Ohms.

The 4.5kW heater would yield 51.2 Ohms @ 480 V, and 47.0 Ohms @ 460-V!

The theoretical and measured Ohms don't even come close! Do you have the actual Vab. Vbc, and Vca voltages related to the measured ph-ph currents Iab, Ibc, and Ica?

Regards, Phil Corso

 

EE... secondly, how were the Ohm measurements taken?

Were they made with the delta intact, or were you able to isolate the three heating elements?

Phil

 

This is a tricky subject although it's made much simpler by not having to worry about power factor.

I would take a guestimate based on calculating the power using the 3 different amperages,
If you want to get the exact kW separate the phases and check the load one element at the time VxA=kW

There is probably a formula for doing this but I use the KISS approach

Roy