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Old March 9th, 2018, 10:02 AM   #1
Timeismoney08
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Power Factor Correction Capacitors

Hello,

I was just curious if a PF correction capacitor is ever used with a VFD install?

Have any of you ever needed to add a PF correction capacitor in any of your builds?



Thank you!
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Old March 9th, 2018, 10:37 AM   #2
AustralIan
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No.

No.
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Old March 9th, 2018, 10:39 AM   #3
Tom Jenkins
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VFDs generally have an inherent high power factor, and there is no advantage to adding capacitors.
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Old March 9th, 2018, 11:38 AM   #4
AustralIan
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Perhaps a line reactor to smooth out harmonic currents?
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Old March 9th, 2018, 11:53 AM   #5
jstolaruk
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I use line reactors; the few times I've been bit by not using them was enough for me to make it standard.
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Old March 9th, 2018, 04:44 PM   #6
jraef
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Quote:
Originally Posted by Tom Jenkins View Post
VFDs generally have an inherent high power factor, and there is no advantage to adding capacitors.
Not only that but when there are VFDs, adding PFC capacitors can actually CAUSE more problems that you otherwise wouldn't have had.
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Old March 9th, 2018, 04:52 PM   #7
janner_10
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Quote:
Originally Posted by jstolaruk View Post
I use line reactors; the few times I've been bit by not using them was enough for me to make it standard.

Out of pure interest, how were you 'bit'?
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Old March 10th, 2018, 05:54 AM   #8
jstolaruk
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Quote:
Originally Posted by janner_10 View Post
Out of pure interest, how were you 'bit'?
On one occasion, I was commissioning a panel with a handful of VFDs and a couple of servos. The servo motion would occasionally act erratic. After much time scratching heads and thinking that it was a tuning problem, I noticed the h/w designer had not designed in line reactors for the VFDs or Servos. I asked the electrician to rummage in their bone yard and install some in the new panel and the erratic behavior disappeared (or never again showed up).
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Old March 12th, 2018, 09:55 PM   #9
2rlp
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What's the difference between using Input reactors v/s Output reactors?
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Old March 13th, 2018, 12:10 AM   #10
Geoff White
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Input reactors stop drive noise from contaminating the supply.
Output reactor reduce the noise on the motor cable and reduce the chance of crosstalk to other cables.
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Old March 13th, 2018, 04:57 PM   #11
snowbanx
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PFC is not needed with a VFD. With a large amount of VFD's in an industrial plant, you may need to look at a harmonic filter.

As stated above, input reactors mitigate some of the noise and harmonics that are sent on the line feeding the VFD. Output reactors are to smooth out the pulsed voltage that is created from the SCR's firing. They are also used to stop the reflected voltage spikes that are created with long leads from the VFD to the motor.
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