VFDs & Power Factor Coorection Capacitors

Hi,

I have this client who has installed an active power factor correction system, all the capacitors totals to about 1400 KVAR. He wishes to install VFDs on his chilling plant 3 X 30 HP VFDs of either ABB or Yaskawa makes.

Will the capacitors pose any problem to the drives, considering the action of switching ON / OFF of the pf correction capacitors?

What measures can be taken to overcome this?

Ron

VFD itself can produce 'reactance capacity'. There are capacitors in VFD's DC-circuit those who do it. Also they are 'small' versus 1400kVAR.

2rlp,

I don't know anything about the active switching part but I'm sure this will not be good. My only experence with power correction caps and VFD's was not good. Chopper brakes had to be installed before they would run even when there was no decelleration. The drives would trip on overvoltage constantly. On these particular units there was a light that was supposed to indicate when the brake was working. The light never came on but the units would run. without the brake module they refused to function. The resistors never got warm either.

I worked in a plant with hundreds of drives and an active PFC bank. We ended up putting isolation transformers in front of the drives to keep them from failing.

You should talk to the drive manufacturer.

2rlp said:

Hi,

I have this client who has installed an active power factor correction system, all the capacitors totals to about 1400 KVAR. He wishes to install VFDs on his chilling plant 3 X 30 HP VFDs of either ABB or Yaskawa makes.

Will the capacitors pose any problem to the drives, considering the action of switching ON / OFF of the pf correction capacitors?

What measures can be taken to overcome this?

Ron

Click to expand...

I am not going to give you a definite yes or no, but I will quote my situation.

A 750 KVA transformer,
with 300 KVAr of active PF control,
300 KW of VFD's , 100 Kw of which are controlling chillers
with out any additional equipment,
We have our capactors near the transformer so there is a low impedence in cabling.
The VFD's are wired with cables that also providing low impedence to the power supply which I feel eliminates problems

I do note that when the transformer gets near full load that the total harmonic distortion noted at the active PF controller starts to rise from less than 4 to a value near 7.
My thoughts on that are that the Impedence of the cabling near full load starts being too high.

I would expect to see more problems with the capacitors than with the VFD's , although I would not want to have more than half the load being consumed by VFD's