Power factor correction

[ssembo]

Hello, i am currently trying to learn about power factor correction but got faced with a problem. I have power consumption details of a certain company but when i calculate its power factor i get 0.38.

From what i have learnt, inorder to get the required kVAr of the capacitors, you have to multiply the kW with the multiplier from the table that corresponds to the new power factor you want to achieve. NOw the problem is, my current power factor of 0.38 is not shown in the power factor table. How do i go about this?


Thank you.

Colin.

 

[RCinFLA]

PF that bad is rare. Some capacitor balasted LED of low power can be that bad.

I assume this is a motor with inductive PF you are trying to correct. What I do is convert the impedance to parallel equivalent and parallel a cap to bring power factor between 95 to 96%. It is generally not a good idea to go all the way to 100% since resonances at switch off can create high surge voltages.

 

[ssembo]

First of all thanks for responding. This is a milling plant whose consumption details i obtained from a utility company. i used the power triangle and thats how i got 0.38pf. i was suprised too but now, how do i determine which size of capacitor i will need to make the pf 0.95. All th calculations i had met did not involve impedances and again, i don't have accesss to the plant.

 

[RCinFLA]

I would be highly suspect that any commercial electric motor would have a 0.38 PF. I think the number is wrong. I the worst run state PF I have seen on a motor is about 0.65.

A very lightly loaded motor may have that poor a power factor.

 

[dr pepper]

Sometimes the pf is written on the motor rating plate, might be worth a phone call to see if one of the lads can see it marked on the plate.

Anyway with a mill esp if its a later one theres usually a speed control for the spindle, either a dc or ac drive, usually to comply with directives such drives have built in power factor correction.

I think you need to contact the machine manufacturer and see what they say about the expected pf.

Where I work we have extrusion machines for polymer, they use lots of energy, and the heaters are inductive as when the pf machine had a failed cap bank the pf went down as low as 0.28, us the maint department aere a little embarassed when the first we knew of it was when the power company came and told us.