## Negative Power Factor

## Negative Power Factor

(OP)

Observing power factor on PQM at one of the sewage pumping station we noticed that power factor become negative (≈-0.85) when one of the pumps is running.

Assuming that some capacitive load in the VFD motor circuitry exist, we can accept this situation.

When there is no pump running pf is 0.98 with 3Φ 6A current and 600V which is correct.

But when the pump is running in bypass mode, bypassing VFD, pf become negative, again (-0.97).

Can you, please, try to explain this to me? Thank you.

Assuming that some capacitive load in the VFD motor circuitry exist, we can accept this situation.

When there is no pump running pf is 0.98 with 3Φ 6A current and 600V which is correct.

But when the pump is running in bypass mode, bypassing VFD, pf become negative, again (-0.97).

Can you, please, try to explain this to me? Thank you.

## RE: Negative Power Factor

I’ll see your silver lining and raise you two black clouds. - Protection Operations

## RE: Negative Power Factor

In the normal world most VFD's exhibit near unity power factor, so you'd expect that when the majority of your load is on VFD, the power factor would be near unity, and when you bypass the VFD, you're back in the world of induction motors, where a power factor of 0.85 would be pretty common.

I'd venture a guess that either your instrument transformers are incorrectly connected of you have an error in your configuration of the PQM.

old field guy

## RE: Negative Power Factor

Actually, the R current at 0.866 power factor and B voltage will present a 150 degrees angle that means -0.866 power factor.

## RE: Negative Power Factor

xnuke

"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand,

Atlas Shrugged.Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

## RE: Negative Power Factor

I’ll see your silver lining and raise you two black clouds. - Protection Operations

## RE: Negative Power Factor

I was on site yesterday and this is what I've captured from the PQMII screen:

Van= 357V at 0 Lag

Vbn= 353V at 240 Lag

Vac= 355V at 120 Lag

Ia = 14A at 334 Lag

Ib = 13A at 207 Lag

Ic = 12A at 95 Lag

Thank you.

## RE: Negative Power Factor

A leading power factor with no load and a lagging power factor when loaded makes more sense.

What do you have that will push the PF leading at no load?

By the way, 334 degrees lagging is close to 26 degrees leading, for what it's worth.

No argument there. But on a practical level, VARs are directed.

If VARs and kW are used to calculate the PF, then PF does become directed.

I suspect that showing PF as positive or negative is an indication of a leading or lagging PF.

The manufacturer is saving space on the display of the Power Quality Monitor.

Please take this as a friendly suggestion David. No disrespect is intended.

--------------------

Ohm's lawNot just a good idea;

It's the LAW!## RE: Negative Power Factor

In fact, leading power factor is with load.

The captured values are with pump running.

Unfortunately I haven't captured exact power factor number, but it was leading.

Thanks again.

## RE: Negative Power Factor

I’ll see your silver lining and raise you two black clouds. - Protection Operations

## RE: Negative Power Factor

"In fact,

indicatedleading power factor is with load."If you have a switchable capacitor anywhere on the system, switch it and see how the indicated PF reacts.

--------------------

Ohm's lawNot just a good idea;

It's the LAW!## RE: Negative Power Factor

Like your thinking Bill.

Keith Cress

kcress - http://www.flaminsystems.com

## RE: Negative Power Factor

IEEE Standard 100 has this as the definition of

arithmetic power factorand definition (B) ofphasor power factor. It's pretty much the basis of the IEC power factor sign convention based on the fundamental frequency. However, remember that real power isn't always positive -- it's defined to be negative per passive sign convention when the device is a source. The IEC power factor sign convention takes this into account, so loads always have a positive power factor sign as they have positive real power and sources always have a negative power factor sign as they have negative real power. This sign convention agrees with textbooks that define power factor as the cosine of the load impedance angle, since in Quadrants I and IV, which both have positive real power, the cosine of any angle is positive. In Quadrants II or III, which both have negative real power, the cosine of any angle is negative.The IEEE power factor sign convention seems to be based on the relationship between the fundamental voltage phasor and fundamental current phasor. IEEE convention appears to use IEEE Standard 100 definition (A) of

phasor power factorto determine the power factor sign, which is "defined by the cosine of the phasor angle between the fundamental sinusoidal phase voltage and the fundamental sinusoidal phase current." If the current phasor lags the voltage phasor (an inductive/lagging load), the angular difference of current with respect to voltage is defined to be negative, and the IEEE convention states the power factor is negative. If the current phasor leads the voltage phasor (a capacitive/leading load), the angular difference is positive, and the IEEE convention states the power factor is positive.xnuke

"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand,

Atlas Shrugged.Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

## RE: Negative Power Factor

You should always check the phasors before you walk away and are recording anyway.

It would be great to actually see the display and the phasors.