PDA

View Full Version : Power Factor for Copeland ZP series 3 Phase Scroll Compressor







bmaneckjee
22-10-2016, 04:46 PM
I'm interested in estimating input power on a 208/3/60 ZP scroll compressor. I have a CT installed over one leg and assuming that the motor coils are balanced and that phase to phase voltage is 208V all I need to know to estimate the power consumption is the power factor for this compressor.

Power in kW = Amps x 3 x 208 / 1.73 * PF / 1000

When I use a PF of 0.9 I seem to be getting higher input power than expected under the load conditions. So either 0.9 is too high or I need to use a corrective factor for the inexpensive 0-5V CT being used.

Anyone know where to obtain the PF for such a compressor or whether it is to be expected that a corrective factor be used with an ordinary CT in a 3P environment?

Brian_UK
22-10-2016, 09:11 PM
How do your results compare with the manufacturers published input figures?

Magoo
23-10-2016, 01:23 AM
a good power factor is around 0.98 to 0.99 which indicates efficient use of drawn power consumed, another factor not in your formula is motor efficiency. should be around 0.9 hopefully.
so as total efficiency increases the drawn power current should reduce.
Power factor capacitors basically balance drawn current to even things out so to speak, dropping the total average.
On large plants automatic power factor correction can reduce power costs hugely, controlling inductive and resistive loads, and peak load penalties.

Greek_engineer
23-10-2016, 11:50 AM
is there any good stack of information with regard to power factor and total efficiency?

bmaneckjee
23-10-2016, 12:51 PM
How do your results compare with the manufacturers published input figures?

That's the problem - input power is higher than max draw values published. The output is bang on and COP is influenced by both of course.

I'm thinking the problem lies with the off-the-shelf CT's which may need a corrective factor to be used in 3 phase applications. However, even with such a correction I would still like to know where to find the power factor.

With regards to the other reply which mentioned capacitors - there are none used in this light commercial 10 ton unit.