Leading Power Factor Issues?
Leading Power Factor Issues?
(OP)
Aside from the associated voltage rise, are there any problems that would likely result from a leading power factor on distribution lines during light load periods?
I am planning to add some fixed capacitor banks to a rapidly growing area of our electric system, and would like to add slightly more than the base KVAR requirement on a few circuits.
I would look at switched banks, but equipment problems in the past have caused me to lose faith in their ability to operate as desired in an unsupervised mode.
Any input on this topic would be appreciated.
I am planning to add some fixed capacitor banks to a rapidly growing area of our electric system, and would like to add slightly more than the base KVAR requirement on a few circuits.
I would look at switched banks, but equipment problems in the past have caused me to lose faith in their ability to operate as desired in an unsupervised mode.
Any input on this topic would be appreciated.






RE: Leading Power Factor Issues?
RE: Leading Power Factor Issues?
RE: Leading Power Factor Issues?
http://www.squared.com/us/products/switchgr.nsf/DocumentsByCategory/6C04856EAABF9DAF852565D400704AD6
RE: Leading Power Factor Issues?
Also on the capacitor issue... Every so often, a local telephone company that rides our poles will ask about capacitor banks that we might have in a particular area where their customers are complaining about telephone line noise. We will typically send a serviceman to meet one of their technicians and remove any capacitor banks in the area from service to help them troubleshoot. As far as I know, taking our capacitor banks offline has never resulted in any improvement in their condition.
RE: Leading Power Factor Issues?
Thanks.
RE: Leading Power Factor Issues?
There may be a penalty for leading power factor from transmission suppliers. One of the transmission providers in the southeast US has the following provision in their Service Agreement for Network Integrated Transmission Service:
"Valley Periods - The Transmission Customer must operate its electrical system in a manner resulting in a 100% power factor or lagging power factor as measured at the primary (high) side of the transformer at the hour of transmission system valley on a monthly basis."
The transformer will add reactive vars, so this allows a somewhat leading power factor on the secondary side.
RE: Leading Power Factor Issues?
I expect to try and install only fixed capacitors on distribution lines. Then add some switched capacitors as needed inside substations where I can monitor them through SCADA. Every manufacturer claims to have great capacitor controls and switches, but each of the ones that I have tried in the past have developed severe operational problems within a year or so.
RE: Leading Power Factor Issues?
RE: Leading Power Factor Issues?
V rise (in %) = (Transformer %Z * KVAR)/(Transformer KVA)
Note: Keep the %Z as a percentage (i.e., do not convert it by dividing by 100)
RE: Leading Power Factor Issues?
It will be interesting trying to comply with this. You won't be able to switch in steps small enough to ensure a 98% pf at all times without going leading sometimes. If you can predict when the transmission supplier peak will occur, SCADA control seems like the way to go.
Make sure that you do at least an approximate calculation of resonant frequency to make sure that it is not near the 5th or 7th harmonic. Example:
5200A fault available at 12.5 kV (112.6 MVA)
4.5 Mvar capacitor bank
resonant h = sqrt(112.6/4.5) = 5 (see IEEE std 519 section 8.2.1.)
RE: Leading Power Factor Issues?
RE: Leading Power Factor Issues?
How do you plan on controlling the capacitors? Time, vars, volts, amps, or some combination?
RE: Leading Power Factor Issues?
We do have a few circuits that have more commercial and small industrial load. On these circuits, I may try to switch based on amps or vars.
Duke used to provide us with a load signal (through NCEMC), but I believe that they stopped doing this a couple of years ago.
RE: Leading Power Factor Issues?
Depending on local harmonic generation and the system resonance frequency, the banks may be required to be in the form of a detuned filter (probably tuned at say 4,8 p.u.). As your target PF is only about 0,96 (as opposed to close to unity)you may resonate above crical frequencies (5th, 7th) and get away without a filter.
Leading VARs are not a problem and voltage rise and potential VAr overloading of transformers are generally all that has to be considered.