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Humble2000 (Electrical) (OP)
4 Jul 06 14:55
Is there anything wrong to have a lead power factor?
We just injecting reative power to the utility right?
I have specified a capacitor banks that will fix the power factor to above .95;however if the load drops the power factor migh lead.
I am aware of step cap. banks but I just want to know what would happen by having leading pf?
itsmoked (Electrical)
4 Jul 06 14:57
I believe you can cause stability problems for the utility if your load can swing between lag and lead. Others will confirm this.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

Skogsgurra (Electrical)
4 Jul 06 17:08
Leading power factor is just as bad as lagging. It means that your reactive power heats cables, transformers and switchgear without doing any useful work. It limits tha available power in a given installation. PF = 1.0 is ideal.

Gunnar Englund
www.gke.org

davidbeach (Electrical)
4 Jul 06 17:15
From the standpoint of heating and losses, the lead/lag of the power factor does not matter.  There can be stability issues as mentioned, particularly around generators.  Running a leading power factor can cause a voltage rise, where a lagging power factor causes a voltage drop.  So, as you swing back and forth between leading and lagging power factor you exaggerate the normal voltage variation, possibly to the point of equipment damage.  Best not to go beyond about .98 leading, better to stay just on the lagging side of unity.
jghrist (Electrical)
4 Jul 06 23:19
Some utilities have a penalty for leading power factor.
tinfoil (Electrical)
5 Jul 06 9:06
Most utilities are still using  revenue meters that cannot (or programmed to be unable to) distinguish between leading and lagging.  If your load is sufficiently leading, you may be penalized identically to the same p.f. lagging.

In all of the utilities I have ever seen, the main circuits tended to run at 80-95% p.f. lagging (depending on load characteristics and line capacitor policies).  So long as your facility is not so large that your leading pf drives the entire utility circuit into leading pf, the utility actually 'wins' (especially if they get to charge you extra for reducing their reactive power flow and supporting their circuit voltage!).
Humble2000 (Electrical) (OP)
5 Jul 06 9:23
Thank you for all valuable replies.

I am mainly concern about the technical problems that this may cause.
As I understood the leading pf can increase the voltage level at the PCC which makes sense.
Instability is a problem that the generation centre would need to concern about and us as a customer have nothing to do with it.

I understand that when we are injecting Reactive power to the circuit that can be used somewhere else in the system , but how this is metered I don know.
Does anybody have a literature on common hydro metering devices?

Regards,
waross (Electrical)
5 Jul 06 20:30
The electro-mechanical meters that were common for 40 or 50 or more years would run in reverse with a leading power factor.
Theoretically this would allow you to "subtract" KVARhrs from your meter during periods of light loading, such as at night when the equipment was shut down but the capacitors were still connected.
In reality, many Utilities installed a ratchet in the meter so that it would not run backwards. When the power factor was lagging, the meter recorded KVARhrs, when the power factor was leading, the meter simply stopped.
respectfully
ScottyUK (Electrical)
5 Jul 06 23:29

Quote:


Instability is a problem that the generation centre would need to concern about and us as a customer have nothing to do with it.

Actally the chances of a generating facility even being aware of it is virtually nil, because the great majority industrial loads are lagging. David's point is valid if you have private generation or your facility is a large part of the load on a embedded generator on the local utility distribution system. In this case the generator may well run into stability problems if it is required to run at a leading power factor.

The people who are more likely to be those who share your utility PCC because their voltage will possibly be affected. If you have your own dedicated transformer or a private HV intake, then any problem is essentially yours and the utility will privately thank you for reducing their VAr loading a little.

----------------------------------
  I don't suffer from insanity. I enjoy it...

Helpful Member!  alehman (Electrical)
6 Jul 06 0:46
If you have local generation, and the generators 'see' leading power factor it can cause voltage stability problems.
ScottyUK (Electrical)
6 Jul 06 2:49
I just said that! smile

----------------------------------
  I don't suffer from insanity. I enjoy it...

itsmoked (Electrical)
6 Jul 06 4:06
I said it first!!bangheadcrylol

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

TestBeforeTouch (Electrical)
6 Jul 06 15:59
I like the quote from Beeman's book. "There are probably more imaginary difficulties associated with capacitors than with any other equipment".

At my plant the utility charges for any lagging PF and none for leading PF, therefore,  we are always leading.
alehman (Electrical)
7 Jul 06 0:31
Scotty/Itsmoked - Not to belabor the point, but I think you guys were refering to possible problems for a utility, unless I am misreading something. I was thinking about a small on-site generator. Sorry if I repeated your ideas.

I reply because I recently experienced this exact problem with one of my clients. There was no problem running on utility power but the backup generator had problems until we removed the capacitor which was causing leading power factor.
itsmoked (Electrical)
7 Jul 06 2:34
I did say utility but should have probably said "generators". But I think we're all more or less correct as we operate on vapors of info.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

ScottyUK (Electrical)
7 Jul 06 2:41
Alehman,

No apology wanted - I'm just poking fun. I was trying to say that a central utility generating plant wouldn't even notice if one small load went from lagging to leading, but an embedded generator belonging to the utility and local to the site might see the change, and an islanded generator belonging to the siteb would be likely  to see an adverse effect if the pf went significantly leading.

We are saying the same thing for sure.

----------------------------------
  I don't suffer from insanity. I enjoy it...

wrong100 (Military)
7 Jul 06 5:37
start
The FCC and power co have decited that
cap loads are bad.
In cap loads current peak leads voltage peak.
In inductive loads current peak lags voltage peak.
 Forty years ago loads were resistive (0 pf) or inductive
(-pf, or laging.

With computers, audio, and so forth, loads have become
leading (+pf).

If your substation is 1000kw and you are using 100kw,
you are 10% of the load, at 10% pf leading or laging
only your meter knows.

Forty years ago power co had sync motors, cap banks,
to correct for lags.

In a nutshell, it costs more in copper/iron to allow
non "0" pf + or -.
davidbeach (Electrical)
7 Jul 06 12:30
Resistive loads have a power factor of 1, not zero; that's why it is referred to as unity power factor.  The reactive factor of a resistive load is zero.
bacon4life (Electrical)
11 Jul 06 16:18
Take a gander at thread238-122851.  

There can also be overvoltage problems if there is too much capacitance at the end of a lightly loaded line.
MineGuy (Electrical)
11 Jul 06 20:47
David Beach,
I dont mean to counteract your statement but
"From the standpoint of heating and losses, the lead/lag of the power factor does not matter"

Just would like to have more insight. Leading power factor means transfer of reactive power back to utility and lagging means from the utility back to load. In both issues, there will be heating as power is flowing. So Could u advise what you mean here. Again, I don't mean you are wrong.
Thanks
davidbeach (Electrical)
11 Jul 06 21:42
MineGuy, for a load of x kW at a power factor of .909, leading or lagging, you have an apparent power of 1.1x kVA.  Given a voltage, that kVA can be converted to amps, and those amps, squared, times the resistance of the line is your losses.  It doesn't matter whether the current is leading or lagging when considering these losses.
asvcmaster (Electrical)
11 Jul 06 22:17
Humble,

I have recently commissioned a 4.3 MVAR\Phase Ungrounded Wye PF Bank at a Clients Shredding Operation (4000 HP Wire Wound Rotor w\Liquid Rheostat). It is Tuned to the 9.8th Harmonic.

At Idle the Bank leads a bit, and it is .94-.97 under load.
The serving Utility does not care about the Leading VAR's, and in this particular application, they will rarely be at Idle.

I would have to say, the Utility, and Application will determine if you can get away with the leading KVAR's.

Mike
davidbeach (Electrical)
11 Jul 06 23:48
In the Pacific Northwest, the principal wholesale power provider, BPA, charges their customers, primarily distribution utilities, a penalty for any power factor below .97, leading or lagging.  I did a long underground feeder fed by one of those utilities once, and they were very concerned that I wasn't going to cause the the customer's load to go leading due to cable capacitance.  Fortunately, at only 14.9kV, the added 4.8 miles of line wasn't going to become a problem.  On the other hand, it was amazing how little voltage drop there was at the end of an 18 mile underground circuit (of which the 4.8 was about in the middle), even with a several hundred percent change in load between summer and winter.
Robert789 (Electrical)
23 Jul 06 15:06
Assuming that we are dealing only with a distribution circuit and not generators, I would mainly be concerned with voltage rise.  If I have the equation correct, the voltage rise can be calculated from the source impedance as follows:
{((KVAR per Phase)/(KVln))/Ibase} * X1 = %VR

The utility won't have to have additional capacity to carry the leading VARs because this will be during periods of light loading, the capacitors will result in freed capacity during peak load periods.  

From the utility perspective, I would rather have you be at 95% lagging on-peak (when VAR support is most needed) and 95% leading off-peak than to have you at, say, 90% lagging on-peak and unity off-peak.  {But our accounting department would still insist on charging you the leading power factor penalty}
DaveScott (Electrical)
23 Jul 06 20:55
I wonder if there are any tuned circuit difficulties, for example, linking a capacitive site to an inductive site?

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