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# Negative Power Factor

07/10/2017 8:47 PM

The utility electric power supply meter was reading a power factor of about -0.85; after installation of an automatic power factor correction equipment, the power factor changed to about -0.95. Can a power factor correction equipment change power factor from negative to positive? How can I change the negative power factor to positive power factor?

With regards

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#1

### Re: NEGATIVE POWER FACTOR

07/10/2017 9:04 PM

Get rid of some capacitors.

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#13

### Re: NEGATIVE POWER FACTOR

07/12/2017 5:47 AM

From here:-

Power_factor

Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors.

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#15

### Re: NEGATIVE POWER FACTOR

07/12/2017 9:10 AM

And there is also a thing called a synchronous condenser (simply a far over-excited generator with no real load on it, but it does apply a continuously variable correction to power factor within a localized region of the grid to which it is phased in.

It only takes a relatively small motor to spin the former generator as I understand it.

Compare this to a switched capacitor bank where there is no continuous adjustment, only steps of adjustment.

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#17

### Re: NEGATIVE POWER FACTOR

07/12/2017 11:34 AM

Whatevah. Then get rid of some inductances. PF is positive in all cases, anyway.

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#2

### Re: NEGATIVE POWER FACTOR

07/10/2017 9:18 PM

Methinks something is wired backwards!

Check the connections on the power factor meter....

Power factor = power/(volts x amps)

If one of these inputs is reversed, the sign will be negative.

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#3

### Re: NEGATIVE POWER FACTOR

07/10/2017 9:46 PM

"...Can a power factor correction equipment change power factor from negative to positive?..." Yes, but it's not necessarily advisable.

"...how can I change the negative power factor to positive power factor...", It depends upon your utility's tariffs, the nature of the load and the type and manufacturer of the equipment, some can, some can't; but if you have to ask then you must rely on expert advice to assist you.

A better question to ask yourself would be, "Why do I want to go from an inductive power factor to a capacitive power factor?"

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#4

### Re: NEGATIVE POWER FACTOR

07/10/2017 9:52 PM

I think this is just semantics. You had a LAGGING power factor of .85, you added PFC equipment, now you have a LAGGING power factor of .95. That makes perfect sense, that is what your power factor correction equipment was intended to accomplish.

The fact that you are reading something with a - sign and want it to read as a + sign is likely just you not understanding whatever that meter is telling you. There is no positive or negative, power factor is relative. It is either leading, lagging, or unity. but some meters use digital symbols like + to show leading and - to depict lagging. Others I have seen use < for lagging, > for leading, 0 for unity.

RTFM...

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#10

### Re: NEGATIVE POWER FACTOR

07/11/2017 2:12 PM

more confusion to the enemy - we have met them, and they r us.

I never ever see that - power factor (<0) in our power plant. But we always have positive VARS. If you ever see negative VARS, you are probably motoring your generator instead of driving it with prime mover, and trouble is imminent.

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#20

### Re: NEGATIVE POWER FACTOR

07/12/2017 9:49 PM

...If you ever see negative VARS, you are probably motoring your generator instead of driving it with prime mover...". A common misconception, and absolutely false. As long as the Watts are positive, the generator is extracting work from the prime mover and pushing real power (Watts) out to the system/load.

VARs, on the other hand, represent the net difference between the MMF (MagnetoMotive Force) from the field and the stator (aka the Air Gap Flux). In a generator the excess MMF from the field represents VARs being pushed out to the system, while if the stator is providing the excess MMF then VARs are being absorbed from the system by the generator. To avoid ambiguity regarding the relative terms leading vs. lagging, it always preferable to use the absolute terms "overexcited" and "underexcited" which refer to whether the stator or the field is providing the excess MMF.

For completeness, when the MMF from both the rotor and the field are equal in magnitude, we define the situation as "Unity PF"; i.e., the net air gap MMF is Zero, and no VARs are produced or consumed, and only Watts are produced by a generator or consumed by a motor/load.

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#21

### Re: NEGATIVE POWER FACTOR

07/13/2017 6:49 AM

If you load up a generator manually, you should note that when you increase the throttle and fuel flow goes up, power factor moves towards "more lead". The excitation current must be increased to keep the power factor at unity or lagging as the kW are increased.

If there is automatic kW loading with power factor control [usually to unity] you will see the excitation current increase with the kW. If power factor control is a "deadband" or proportional control it will tend to load & finish at a small lead, say 0.98, because it follows behind the kW. If your system is not on a Grid or is unusual, the power factor will control to that of the load, or maybe, a VARs which keeps the power factor at the Grid connection to unity, compensating local load power factor.

Note that, in the last paragraph, RAMConsult meant to type "stator and field".

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#5

### Re: NEGATIVE POWER FACTOR

07/10/2017 10:30 PM

..."Working Power – the “true” or “real” power used in all electrical appliances to perform the work of heating, lighting, motion, etc. We express this as kW or kilowatts. Common types of resistive loads are electric heating and lighting.

An inductive load, like a motor, compressor or ballast, also requires Reactive Power to generate and sustain a magnetic field in order to operate. We call this non-working power kVAR’s, or kilovolt-amperes-reactive.

Every home and business has both resistive and inductive loads. The ratio between these two types of loads becomes important as you add more inductive equipment. Working power and reactive power make up Apparent Power, which is called kVA, kilovolt-amperes. We determine apparent power using the formula, kVA2 = kV*A.

Going one step further, Power Factor (PF) is the ratio of working power to apparent power, or the formula PF = kW / kVA. A high PF benefits both the customer and utility, while a low PF indicates poor utilization of electrical power.

Here is an example.

A steel stamping operation runs at 100 kW (Working Power) and the Apparent Power meter records 125 kVA. To find the PF, divide 100 kW by 125 kVA to yield a PF of 80%. This means that only 80% of the incoming current does useful work and 20% is wasted through heating up the conductors."...

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#6

### Re: NEGATIVE POWER FACTOR

07/11/2017 3:03 AM

"Can a power factor correction equipment change power factor from negative to positive?" No, it cannot. The energy flow depends on the generator and on the load.

"how can I change the negative power factor to positive power factor" Negative power means that you are measuring generated power. Reversing voltage or current leads of the Meter will give you the opposite value.

The best you can do is to ask the installer of the meter.

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#7

### Re: NEGATIVE POWER FACTOR

07/11/2017 8:08 AM

One interpretation of "lagging" is that it is "late," "behind" - hence negative (-).

On the other hand, the conventional rotation of vectors in electrical diagrams is anti-clockwise, while mechanical clock displays rotated "clock-wise" for centuries and still do. Correspondingly, the complex number impedance of a series R-L circuit is R + jwL & R-C is R - jwC, hence inductive loads can be regarded as positive.

I once had a job for which I had to, after it was finished, change the meter scale [legend] and fit an inverting amplifier. This was because all the customer's existing meter needles in central control moved left for lag and right for lead. There were two conventions operating, old and new.

In answer to the question, it is technically possible to over-compensate for inductive loads to give a capacitive load to the supply.

However, if you look at the vector triangle for an 0.95 lagging power factor load, you will see that the perpendicular side of the triangle is 0.3 long. This means that to cancel this lagging current [with an equal leading current] there must be capacitors drawing over 30% of the active current.

This means that to reduce the supply current by 5% (1.0 to 0.95), capacitors drawing 6 times the reduction in supply current must be used. The cost of this is just not worthwhile for the reduction of supply current.

If 0.75 corrected to 0.95 is considered, capacitors drawing 28% of the 0.75 power factor line current give a 27% reduction of line current.

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#8

### Re: Negative Power Factor

07/11/2017 1:41 PM

Creating a positive power factor is an expensive and pointless indulgence. Utilities will charge for a leading power factor the same as lagging.

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#9

### Re: Negative Power Factor

07/11/2017 2:07 PM

Since power factor is power/(|volts|*|amps|), a negative power factor indicates the load is generating power, which might be the case of a residence with solar power selling electricity back to the power company.

"A negative power factor occurs when the device (which is normally the load) generates power, which then flows back towards the source, which is normally considered the generator.

For example, if an induction motor is used to operate an electric railway locomotive, the power factor will be lagging by less than 90 degrees as the locomotive climbs a hill. If the motor is nearly loaded, the power factor might be about 0.85. If the track is level at the top of the hill, the motor's load will be reduced and the power factor might drop to 0.65. As the locomotive begin to go downhill, the power factor drops more and may be come negative as the motor begins to operate as a generator returning braking power to the source.

However, the fact that PF is negative means that active power is negative too. When you are considering a load, this means that the load outputs energy to the system, so it works as a generator. If you would consider a generator, the negative active power means it works as a load, so it takes energy from the system. This can happen in fact in one and only state, when the generator's turbine failed and rotation of the rotor is created by rotating magnetic field of the system (the generator works as a motor and it is rotating the turbine)."

https://www.quora.com/What-is-a-negative-power-factor-What-are-the-reasons-for-this-Is-there-any-harmful-effect-on-a-small-capacity-gas-engine-for-a-negative-power-factor

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#11

### Re: Negative Power Factor

07/11/2017 3:32 PM

Power factor is the cosine of [90deg >= angle in question >= -90deg], therefore it cannot in itself be negative.

While power factor correction equipment can introduce a leading power factor, the closer the figure is to 1 the better, leading or lagging.

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#12

### Re: Negative Power Factor

07/11/2017 5:15 PM

"Power factor is the cosine of [90deg >= angle in question >= -90deg], therefore it cannot in itself be negative."

Thank you, yes, that was my point earlier. From a strictly engineering standpoint, "negative power factor" for a LOAD (not a generator) is not a valid concept. Hence my supposition that this original query is itself based on a misinterpretation of a value, likely displayed on a meter that is using the - sign to simply indicate that it is lagging. Nothing else makes sense.

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#14

### Re: Negative Power Factor

07/12/2017 9:07 AM

Nicely done, old sport, credit for stating the obvious, but stating it in a clear and concise, and correct manner.

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#16

### Re: Negative Power Factor

07/12/2017 9:18 AM

Positive power factor, at a utility tie point, indicates generation or sourcing of power. Negative power factor (induction loads) is a consumer. If the plant's utility tie is positive, it is supplying power to the grid. A -0.95PF is very good, anything < -0.85 typically incurs a penalty. To keep the discussion simple, the more negative the power factor, the more "imaginary" power is being consumed. Imaginary power is essentially heat and no work. A locked rotor would have a PF of -0.00 for example. In supplying the plant with the Real KW needed to do the work, as the plant's power factor goes more negative, the utility has to produce more power which costs all rate payers money. The plants utility meter only reads real power delivered (by Regulation). This is the reason for penalties for PF's <-0.85. It is suggested to discuss the situation with the local utility as many may offer cost sharing to correct this as it raises rates when new units need to be built, no one likes this.

Power factor correction can be had with a number of options, of which Cap banks were mentioned but employing a synchronous motor on a steady load such as a base loaded compressor and adjusting the excitation is another technique. Synchronous motors operate with a leading or + PF.

In summary, a -0.95PF is nearly ideal and efforts to improve on this would not be cost effective as the gain versus cost is non linear above -0.95. Whoever helped you get to this point, did a great job.

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#18

### Re: Negative Power Factor

07/12/2017 3:57 PM

Your PF correction stepper capacitor bank was not properly designed or outfitted. Your stepper PF bank of correction capacitors was overrated. My advice is you temporarily disconnect the stepper and measure the lagging power factor, make an inventory of the inductive equipment (Motors, Ballasts, Inductors, etc.) and re-caculate the required total PF capacitor correction for a .98 PF target value, divide this total by the number of steppers steps stops and install this number in equal VAR values (for each step position) insuring the stepper will not overcorrect if the original low PF value does not change. Try to establish a .98 PF upper target to insure that you will never overcorrect.

Note: If there are motors which continuously go in and out of the line, the stepper will never be able to properly correct to an optimum PF value.

A) First correct your Motors as much as you can with the appropriate 'Motor Mate' capacitor units (use fuse type disconnects) to insure each motor starts and runs with its own PF capacitor unit which will go in and out of the line when each motor runs and stops. Most of the remaining inductive load now is of a static nature so you can assume it will not vary in time.

B) When all 5-HP or bigger motors have been retro-fitted with 'Motor Mate' units, measure the remaining PF value and re-calculate your equal stepper PF capacitor step value to reach the .98 target.

As I said before, even when properly designed, steppers alone seldom ever correct to a satisfactory PF target value, because if there are uncorrected motors across the line, every time a large motor goes in and out of the line ,its inductive PF will upset the predesigned stepper discrete step correction limit and almost always, the stepper will under or over correct to an unsatisfactory PF value which will never be near the ideal .98 PF target.

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#19

### Re: Negative Power Factor

07/12/2017 4:27 PM

Cleverly stated answer, sir. I respect that immensely.

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#22

### Re: Negative Power Factor

07/13/2017 8:04 AM

There are several posts here that are either written badly, as to me they make no sense at all.....

Mostly the most recent ones!!

Here is a web page that explains it far better than anyone else here has up to now done (and I haven't trusted my over 50 years old knowledge completely either!):-

True-reactive-and-apparent-power

...and it makes sense and agrees with what I was taught in the 60's.....!!!

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#23

### Re: Negative Power Factor

07/13/2017 9:33 AM

Nicely done, salute!

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#24

### Re: Negative Power Factor

07/13/2017 1:22 PM

A good description of real, reactive and apparent power!

But the original post was really asking how power factor can have a negative value, which gets even more negative when it is "corrected".

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#25

### Re: Negative Power Factor

07/13/2017 2:07 PM

If a Power Factor of 1.0 equals 100% Resistive Load and 0% Reactive Load, then the 'sign' of the Power Factor indicates which reactive element is 'overbalancing' to its side. a positive PF < 1 would indicate too much inductance, a negative PF would indicate too much capacitance.

Since Power Factor correction equipment is normally designed to balance inductive loads, they are designed to shift varying amounts of capacitive load onto the circuit. that corrects excess inductance, but only increases excess capacitance. That is why the PF goes more 'negative,' You're already 'overcorrecting' without the added gear, and the new gear only 'overcorrects' further.

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#26

### Re: Negative Power Factor

07/13/2017 4:46 PM

So, if the guy removes all his capacitor banks, he should be seeing a substantially below unity, but positive PF... interesting. He was requested to do that experiment at least once.

You might just be right, and then where would we be voting you OT on this answer, I think that is over-reaction on someone's part (pun intended).

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#27

### Re: Negative Power Factor

07/14/2017 2:31 AM

We always used "leading" and "lagging"!

As I remember,the following was just about what he was saying, and I still find it easier to "follow", but it includes details of "minus" and "plus" as well for clarity. The underlined sentence is MOST important I feel....:-

If the resulting current phase angle is more negative in relation to the driving (source) voltage phase angle, then the power factor is said to be "lagging".
If the resulting current phase angle is more positive in relation to the driving (source) voltage phase angle, then the power factor is said to be "leading".
So if the driving voltage phase angle is $\theta$ deg and the resulting current phase angle is $\phi$ deg.
If $\theta$ > $\phi$ power factor is lagging.
If $\theta$ < $\phi$ power factor is lagging.
Then if $\theta$ = $\phi$ power factor is unity and neither leading nor lagging.
The driving (source) voltage phase is often assumed to be zero (for convenience) and in that situation it is immediately obvious that a lagging power factor condition is indicated by a negative sign for the current phase angle. Similarly a positive sign for the current phase angle indicates a leading power factor.

Can we all agree with this?

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#28

### Re: Negative Power Factor

07/16/2017 7:33 AM

There may be two possibilities,

1) Error in CT polarity connections

1) Error in CT polarity connection:

In PF meter, secondary of CTs in R&B phases are connected to the M( Main ) & L( Load ) terminals ( two sets ) and three secondary (E1, E2 &E3 ) terminals of PT are connected to three potential terminals of PF meter. If there is wrong CT polarity connection in one phase, the PF meter will show negative reading.

In case of over compensation, proper load study must be done before any installation of APFC panel since supplying leading VAR to the utility is very detrimental.

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#29

### Re: Negative Power Factor

07/16/2017 8:46 AM

Sorry to say this, but (and you are not alone) appear to not to understand the question clearly, if I read your answer.

So here its is again:-

The utility electric power supply meter was reading a power factor of about -0.85; after installation of an automatic power factor correction equipment, the power factor changed to about -0.95.

(Which is a "good" correction to my mind, closer to unity! In my day, that would have been considered to be quite reasonable!)

Can a power factor correction equipment change power factor from negative to positive? How can I change the negative power factor to positive power factor?

The answer being "OF COURSE IT CAN!!" In this case, even more capacitance would be needed.....In the past, I have been told that to achieve unity, which is of course best, was/is not financially worth the effort, with what are usually inductive loads....

I also feel that many here are misinterpreting the meaning behind the usage of "Positive" and "Negative" power factor!! Badly even!!

Which is why I reiterated (again), the clearer and better usage of the words "leading" and "lagging".......which is showing far more clearly that the voltage and current are not in phase with each other and where they are with repect to each other!!

Minus is not "bad" and "plus" is not good!!!! In fact, both leading and lagging are similar problems. Unity is best!!!

I am constantly surprised by the misunderstanding of otherwise seeming well informed people on that simple point alone.....

As some of the posts here are apparently simply giberish!!! According to some, normal PF corrections apparently making it "worse" not better, DUUHHH! Now that I really don't understand at all!!!

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