Power Factor - Leading / Lagging

[Bugman1400]

In my experience, harmonics are quite often a contributing factor in PFC failures.

In one paper mill every element in a bank of automatic PFC units had failed. Paper machines use variable speed drives which have a high harmonic content. This was not taken into account and no mitigation measures were in place.

I agree with your assessment on harmonics as well. I have also seen caps fail at the substation because the load being served was a large arcing-type boiler.

 

[Ingenieur]

Where did the 8200 come from? Isn't the nominal operating at 7967V?

cap rating is 8320
actual operating is 14200 LL or 8198.4 LN (I rounded to 8200)
pf went from ~0.963 to ~0.960, negligible

system rated is 13.8
motor rated is 13.8 (OP says 13.2 should have been spec'ed)
system actual operating 14.2 1.029 PU

 

[Bugman1400]

cap rating is 8320
actual operating is 14200 LL or 8198.4 LN (I rounded to 8200)
pf went from ~0.963 to ~0.960, negligible

system rated is 13.8
motor rated is 13.8 (OP says 13.2 should have been spec'ed)
system actual operating 14.2 1.029 PU

I think the operating is 13.8kV which is 7967.

.......nevermind. I read the OP's first post that said the motor was fed at 13.8 and took that to mean the operating was 13.8 but, now I see later in the thread that the voltage does go to 14.2.

 

[Open Neutral]

I'm curious re: the original question.
What are the disadvantages of over-correcting into leading? (Assuming no POCO PF charges)

 

[Ingenieur]

I'm curious re: the original question.
What are the disadvantages of over-correcting into leading? (Assuming no POCO PF charges)

One factor
surge impedance Zg = sqrt(L/C)
as C gets larger Zg gets smaller
this determines the magnitude of the asymmetric fault (or switching) current magnitude

no real gains in eff above 0.95 pf

 

[Open Neutral]

no real gains in eff above 0.95 pf

I asked because eons ago I had to add switching to enable C when motors were running but not when off.
I always wondered what the downside of not-switching them out would be....

 

[Besoeker]

One point not yet mentioned unless I missed it it that over correction can result in a terminal voltage increase.

 

[meternerd]

What is the disadvantage of running a motor with a leading power factor? I've heard that in a sense you are giving reactive power back to the utility company, but wouldn't one advantage be that a leading power factor would try to improve the overall power factor of your facility / plant? In our case, this is an 8500 hp motor that's fed with 13.8kV. What if we ran this motor at a leading power factor? We don't get charged for poor power factor anyway.

If you don't get charged for PF, why bother? The utility may install PF correcting Cap banks, but if they don't require you to do so, and there's no financial incentive, most customers we have don't. We only charge for KVAR if it's over a 50 KVA service.