power factor correction equipment sizing

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mwuniseal

Member
I need some help in sizing power factor correction equipment. I understand that there is much involved, so I will just start with the basics. Our switchgear is fed from a 1333 kva transformer at 8.0 % impedence. The secondary of the transformer is 480/277 3 phase wye with a 1600 amp main.We currently measure current and power factor. Current averages 700 amps and around 1200 amps at peaks.The power factor averages around 85%. That is all the information that I have at this time. What else do I need to have to figure what size kvar equipment I need. Any information is greatly appreciated.
 

Besoeker

Senior Member
Location
UK
I need some help in sizing power factor correction equipment. I understand that there is much involved, so I will just start with the basics. Our switchgear is fed from a 1333 kva transformer at 8.0 % impedence. The secondary of the transformer is 480/277 3 phase wye with a 1600 amp main.We currently measure current and power factor. Current averages 700 amps and around 1200 amps at peaks.The power factor averages around 85%. That is all the information that I have at this time. What else do I need to have to figure what size kvar equipment I need.
The power factor you wish to attain and some data on how power factor varies with loading.
 

bob

Senior Member
Location
Alabama
I need some help in sizing power factor correction equipment. I understand that there is much involved, so I will just start with the basics. Our switchgear is fed from a 1333 kva transformer at 8.0 % impedence. The secondary of the transformer is 480/277 3 phase wye with a 1600 amp main.We currently measure current and power factor. Current averages 700 amps and around 1200 amps at peaks.The power factor averages around 85%. That is all the information that I have at this time. What else do I need to have to figure what size kvar equipment I need. Any information is greatly appreciated.

KVA? = KW? + KVAR?. KVA = KW/PF. You should be able to determine the KVA, KW and PF from the utility metering and your bill. You decide what you want the PF to be and calculate the required KVAR to make it happen. From there you get the size of the KVAR equipment.
 

jghrist

Senior Member
Assuming that the power factor is 85% at the peak load of 1200A, then using Bob's formulas:

First calculate the reactive power without power factor correction:

kVA = 1200A?0.48 kV?sqrt(3) = 998 kVA
kW = 0.85?kVA = 848 kW
kvar = sqrt(kVA? - kW?) = sqrt(998? - 848?) = 526 kvar
This is the reactive power requirement of the load

To get to 95% pf with the same kW load,

kVA = kW/0.95 = 848/0.95 = 893 kVA
kvar = sqrt(893? - 848?) = 280 kvar
This is the most net reactive load you can have after correction to keep the power factor at 95%.

To make up the difference between the 526 kvar and 280 kvar, you need 526 - 280 = 246 kvar of capacitors (82 kvar per phase).

You can do similar calculations at other loads to determine how much can be fixed (to correct at minimum load) and how much each capacitor step needs to be.
 

Shoe

Senior Member
Location
USA
Any particular load(s) resulting in reduced power factor? It's best to put the reactors at the load and switched with the load rather than the service entrance.
 
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