Power Factor
Power Factor
(OP)
A trick question regarding lagging and leading power factor:
Is this determination based on the direction of var flow (in or out), or is it based on watt and var flow in the same direction?
If watts and vars are flowing out of a substation, we have a lagging PF.
If watts are flowing out, and vars are coming in, we have a leading PF.
What about watts in / vars in?
and watts in / vars out?
Can a PF be lagging at the feed end of a line and leading at the load end of a line?
Is this determination based on the direction of var flow (in or out), or is it based on watt and var flow in the same direction?
If watts and vars are flowing out of a substation, we have a lagging PF.
If watts are flowing out, and vars are coming in, we have a leading PF.
What about watts in / vars in?
and watts in / vars out?
Can a PF be lagging at the feed end of a line and leading at the load end of a line?






RE: Power Factor
The convention is that inductive loads (current lags voltage) has negative P.F. while capacitive loads (current leads voltage) has leading P.F.
Gunnar Englund
www.gke.org
RE: Power Factor
If watts and vars are flowing in opposing directions, power factor is leading.
So for an induction motor - power is flowing into the motor, reactive power is flowing into the motor - power factor is lagging.
Synchronous generator that is producing vars - watts flowing out, vars flowing out - power factor is lagging.
Capacitor bank - power flows in (losses), vars flow out - leading power factor.
There is an IEEE metering standard that is generally depicted in any power meter instruction book that covers this. If you go to the GE website and download the instruction book on their PQM, I believe you will find a diagram there.
Also, you might search this forum - there have been some extended discussions on this in the past.
RE: Power Factor
ELI: Current(I) is after ('lags') voltage (E), in an inductive (L) load.
ICE: Current is before ('leads') voltage in a capacitive (C) load
RE: Power Factor
RE: Power Factor
Yes if it is a short heavily-loaded line and the load is capacitive.
The model for a short transmission line is a simple series inductance.
Let's say the load is dissipating 10MW and producing 1MVAR (leading since MW and MVAR flow in opposite directions).
Let's say the transmission line at this loading level dissipates 3MVAR in the series inductive element.
We have to injuect 10MW and 3-1 = 2MVAR at the supply end. Since P and Q are in the same direction this is lagging.
Note this scenario becomes less likely with longer tranmission lines where the equivalent circuit includes a a shut-capacitor at the end.
The more likely scenario with a long transmission line is that we may have an inductive load at the load end and leading power factor at the supply end (due to line capacitance generating more MVAR than is used by the load)
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