Power Factor Correction at motor Terminals. In rush current.
Power Factor Correction at motor Terminals. In rush current.
(OP)
I was in a discussion:
http://www.eng-tips.com/viewthread.cfm?qid=368907
...and the consencus was that placing a capacitor at the motor terminals does not increase the inrush current. I can't find it so .... Here is a link:
http://ecm web.com/co ntent/corr ecting-pow er-factor- your-motor -terminals.
http://www.eng-tips.com/viewthread.cfm?qid=368907
...and the consencus was that placing a capacitor at the motor terminals does not increase the inrush current. I can't find it so .... Here is a link:
http://ecm
Quote:
There are, however, limitations on capacitor size when connecting capacitors this close to the motor terminals. These limitations are products of self-excited motor overvoltage (of as high as two times source voltage) and excessive inrush current (of as much as 20 times normal full-load current). Subsequent transient torque caused by out-of-phase reclosing before the capacitor can discharge can also play a part in limiting capacitor size.





RE: Power Factor Correction at motor Terminals. In rush current.
See http://gke.org/presentationer/files/PFC%20and%20Mo...
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Power Factor Correction at motor Terminals. In rush current.
RE: Power Factor Correction at motor Terminals. In rush current.
RE: Power Factor Correction at motor Terminals. In rush current.
RE: Power Factor Correction at motor Terminals. In rush current.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Power Factor Correction at motor Terminals. In rush current.
I've never bothered measuring a capacitor/motor combination but I have measured capacitors by themselves and they typically have a high frequency ringing inrush. So, I would expect the very first answer from David provided in the other thread is exactly what happens. You'll get the 1/4 to 1/2 cycle capacitor ringing superimposed on top of the motor current. I'm not sure why there had to be this redundant thread about it.
RE: Power Factor Correction at motor Terminals. In rush current.
One thing that I found is that the risk of self-excitation seems to be quite a bit exagerated. Large capacitors prolong the decay of induced voltage (keep rotor flux up), but there was no sign of overvoltage. At least not on the small motor. Haven't looked in detail at the "larger" one.
I'll sit down and collect a few zoomed recordings. Ready in a few hours.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Power Factor Correction at motor Terminals. In rush current.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Power Factor Correction at motor Terminals. In rush current.
I haven't been able to stop my lights from blinking, but maybe by adding additional capacitance when the motor starts may have an effect. I'm wondering if adding the capacitance will reduce the duration of transient, as opposed to reducing the magnitude of the transient?
RE: Power Factor Correction at motor Terminals. In rush current.
thread237-241267: Discharging PFC capacitors
I’ll be happy to be proven wrong (since that means I’ll learn something). Or maybe it won’t be a matter of right/wrong but just looking at things differently. I look forward to seeing your post.
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(2B)+(2B)' ?
RE: Power Factor Correction at motor Terminals. In rush current.
I am getting curious now and will look for larger motors with capacitors connected to the terminal. The problem is that most people probably will get nervous when I mention that I want to do this kind of test. Time for some googling, I think.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Power Factor Correction at motor Terminals. In rush current.
RE: Power Factor Correction at motor Terminals. In rush current.
Regarding the overexcitation – I’ve got to admit I was surprised to see no peak in the decaying voltage after disconnecting the overcorrected motor. So I immediately looked for a reason to dismiss it and settled on resistance. But then again, if that was the whole story I’d still think at least there would be a at least a little blip in the voltage as passing through resonance. So maybe there will be some other lesson to be learned in studying the details.
Do you know if the motor stator was wye or delta wound?
=====================================
(2B)+(2B)' ?
RE: Power Factor Correction at motor Terminals. In rush current.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.