How to correct for a Leading Power Factor (kVArh)

[Harsh864]

Hi guys,

We have a industrial connection of 225 kW.
Our industry consists mostly of Induction motors and runs in night shift mostly.
So we use capacitor banks for lower factor correction. And so far we have maintained 0.995-0.999 pf (sometimes even 1) over the years.

Previously, the power factor was calculated as
P.f. = kWh / ✓(kwh^2+kvarh_lag^2)Recently, our energy provider changed there of calculation technique and our meters to record kvarh_lead also.

And new formula is

P.f. = KWH / ✓(kwh^2+(kvarh_lag+kvarh_lead)^2)Due to this our p.f. is reduced to 0.200 to 0.225

Looking at the metering reading, I can notice that kvarh_lead is increasing very fast.

What should be done to correct p.f.
Is it the capacitor bank or something else.

 

[Windadct]

This seems very different than how this is done in the USA. But - are you paying for PF or for KVARH(lag) ? [ Example here in the USA you pay for what they measure, kVARH - and this is only for commercial connections.] In your case it seems they are measuring VAR - but billing for the PF which they calculate? ( In my opinion - this is really a bad process or practice.)

Technically PF based on only the Lagging aspect of the load is not accurate. I suspect that you have had too much correction ( capacitance) on line and frequently have a leading power factor, but since the calculation did not consider this, your PF calculation was "wrong".

PF technically is the ratio of Real to Apparent power, where KWH is energy , and VARH is ? .. "apparent energy" - but I have not heard that term used often. The distinction I am trying to make is the difference between power ( instantaneous flow or a rate ) and Energy ( cumulative quantity).

A leading power factor may be disruptive to the other local customers, so in general it is to be avoided, however usually customers are lagging, so your capacitors may be providing Capacitance = Leading VARs, to compensate for other utility customers lagging loads.

It sounds like you have fixed capacitance on line, and as the inductive load is varied sometimes you have too much capacitance on line.

One way to address this would be to move some of the capacitance to only be on line when the larger motors are on line ( running)

The Wikipedia on PF is pretty good, it is well worth the read.

 

[Harsh864]

We are in Industrial area. And our connetion is high tension line of 11kv.

We pay electricity charges based on kWh only.
Incentive is given on pf 0.95 and above(half percent for each 0.01)

Penalty is levied on pf 0.90 and below (half percent for each 0.01)
(on a percentage basis of electricity charges)Yes, we have put up the capacitor banks after the transformer and before the LT bus bar system.

Calculation steps and formula is provided by the energy supplier and I have cross checked it with the previous month bill.

When we run the factory for 12 hours / 2days / 3 days..
The p.f. comes at 0.94 for that period.

And if the factory is not operating for 1 day, then the p.f. for that particular time period goes to 0.2. ( average for the whole period goes to 0.78).

 

[jim hardy]

And if the factory is not operating for 1 day, then the p.f. for that particular time period goes to 0.2. ( average for the whole period goes to 0.78).

That'll cost you plenty, eh ?
What you'll have to do is quit drawing so much leading KVAR when your load is light.

One way to address this would be to move some of the capacitance to only be on line when the larger motors are on line ( running)

that's the most foolproof approach, move the capacitors to the motor feeds.

Or automate, ie measure power factor and switch capacitors as required to keep it above 0.95

 

[Harsh864]

Yes, this change is brought last month only, we became aware after checking the bill.

Yes, I will be consulting for moving the capacitor to larger motor feeds.

What you'll have to do is quit drawing so much leading KVAR when your load is light.
Or automate, ie measure power factor and switch capacitors as required to keep it above 0.95

This is what I am looking for. how to do it.

Will the dynamic power correction system help me.
As this system is for switching load real time and used for system where load is changed frequently.
And in my case load is constant for atleast 12hour shift.

Or the harmonics system will help me.?

 

[jim hardy]

Will the dynamic power correction system

That name sounds like something that would help, but i have no idea what it is you are describing.

As this system is for switching load real time and used for system where load is changed frequently.
And in my case load is constant for atleast 12hour shift.

Think about this for a little while
if every motor circuit were corrected to pf>95% by wiring a capacitor in parallel with the motor, would your factory pf be >0.95 ?
At first glance one would think so
and you'd need no automatic switching.

I think i'd want to do some experimenting before settling on a solution.
Try first moving capacitors to individual motor feeds and see if it helps.

Eventually i think some sort of 'smart' device would be your best bet - it won't forget to 'throw the switch'.
Here's first hit i got from Google search on "dynamic pf correction" , not a recommendation or endorsement, we don't advertise here
just read their brochure and search on the unfamiliar terms. Expertise begins with vocabulary.
http://www.eaton.com/Eaton/Products...PowerFactorCorrection/LV-AutoVAR300/index.htm

Or the harmonics system will help me.?

What harmonic system ?
I don't think your problem is harmonic related.

 

[Madhuri]

I am facing the same problem. How you solved it? LED installed in the premises gives leading pf and we are getting penalties for every month even though we installed APFC panel.

 

[anorlunda]

I am facing the same problem. How you solved it? LED installed in the premises gives leading pf and we are getting penalties for every month even though we installed APFC panel.

Your automatic power factor correction (APFC) must not be working correctly, or not set up correctly. I would seek help from the APFC manufacturer. I would also ask for engineering help from the power company to diagnose and fix the problem.

 

[Madhuri]

When APFC is not in the circuit and LED lighting load is there on the system PF is leading so no use of APFC at night. We are planning to install inductors in between. Please guide.

 

[anorlunda]

When APFC is not in the circuit and LED lighting load is there on the system PF is leading so no use of APFC at night. We are planning to install inductors in between. Please guide.

That is not the kind of decision you should make based on the opinion of strangers on the Internet operating with limited information. You should hire a professional power engineer.

Thread closed.