Power factor correction and inverters

[Magnum]

I am not sure why you say no in response to me saying that what @Rickster said is correct? Especially since your following comments support what he said...

No you pay for Difference between KW and KWA this is for Single Phase and 3 phase installation. Industrial clients get a report every month on the Power factor difference and get fined extra. this does not include the Extra wear and tear you cause to infrastructure due to the Extra load you draw at high inductive loads. Even though a machine draws 3KW the incoming power draw can be 4KVA exceeding instalation limits when running pure Inductive load. you rarely Trip the Breakers in residential setups hence almost no one out there know about Power factor. Only a few artisans, Guys that had Electrical at school and colledge ect even knows it exist.

 

[Kawak]

What is the total load? Compare that with the difference and then decide if PF is going to have any effect and benefit.
What is the voltage AND frequency stability like when you notice the motors making funny noises?

Resistive loads are pure loads kW = VA, hence the PF = 1. Adding resistive loads generally stabilises any PF issues. ( makes the difference between kW and VA less significant.)

When the resistive total load is reduced ( no geysers, kettles, etc are running) the inductive loads become more significant, hence it sort of makes sense that you notice these issues at those times.


Do you know that the motors are working properly and do not have capacitors in them that are busy dying on you?

No personal experience of the small devices being sold.

A typical residential load is almost entirely resistive. BUT that changed when we all started using CFL lamps and LEDs and more and more inverters etc.

I presume that it would not require anything substantial to correct any PF issues in a typical home. However, without someone doing some proper measurements first, it would not be possible to just assume those tiny gadgets would be really doing anything more than making the snake oil salesman rich.

You are correct, I have an induction hob, using that makes the 2 numbers differ by over 340, when the oven is on, the number closes to within 40, load during that time registers around 2kva x 2 inverters and generally 2.34kw per inverter. But that gap closes massively when the oven is used.

The motor that I know acts this way is my pressure boosting pump which I can hear from the kitchen and begins to sound like it's seriously low on power, any way to test if capacitor is dying? Or maybe I can just change it, local shop sells the capacitor for just R110.

 

[Kawak]

https://electrical.theiet.org/media/1687/power-factor-correction-pfc.pdf

This pdf explains it really well

Good read, though my non electrician brain still don't really know why it happens, it feels like motors are designed wrong to need something that is out of phase to power itself, makes sense that correcting it saves energy. Will the saving equate to actually using less of my battery if I ever go off grid? Will going off grid make PFC worthwhile for a home install?

 

[Neuk_]

No you pay for Difference between KW and KWA this is for Single Phase and 3 phase installation. Industrial clients get a report every month on the Power factor difference and get fined extra. this does not include the Extra wear and tear you cause to infrastructure due to the Extra load you draw at high inductive loads. Even though a machine draws 3KW the incoming power draw can be 4KVA exceeding instalation limits when running pure Inductive load. you rarely Trip the Breakers in residential setups hence almost no one out there know about Power factor. Only a few artisans, Guys that had Electrical at school and colledge ect even knows it exist.

I am still not understanding why you are disagreeing? What @Rickster posted is correct, PFC is mainly used by very large industrial electricity users with one reason being because they are billed very differently to residential users.

 

[Magnum]

I am still not understanding why you are disagreeing? What @Rickster posted is correct, PFC is mainly used by very large industrial electricity users with one reason being because they are billed very differently to residential users.

You don't only pay extra if you use 3 phase.

 

[Kawak]

I am still not understanding why you are disagreeing? What @Rickster posted is correct, PFC is mainly used by very large industrial electricity users with one reason being because they are billed very differently to residential users.

Im guessing large industrial consumers are billed for KVA and not KW like us home users?

 

[Neuk_]

You don't only pay extra if you use 3 phase.

Who said otherwise?

 

[Neuk_]

Im guessing large industrial consumers are billed for KVA and not KW like us home users?

I am not entirely sure to be honest, I'll ask my FIL some time, he did explain at some stage the there is a charge for large industrial users related to their max kW used within a small time frame.

 

[Magnum]

Who said otherwise?

The whole post is that Only 3 phase pays extra as they use different meters. Everyone pays extra. 3 phase in industrial aplications gets Fined extra. Even farms will most likely only pay per phase and it is to the users advantage to balance the phases for reading purposes as they still use old meters. And an imbalance can only be detected with excessive meter readings on a single phase. Right now we are sitting with a R15mil Eskom bil for the month. I have helped the Chief a couple of times with some Calculations.

 

[Neuk_]

The whole post is that Only 3 phase pays extra as they use different meters. Everyone pays extra. 3 phase in industrial aplications gets Fined extra. Even farms will most likely only pay per phase and it is to the users advantage to balance the phases for reading purposes as they still use old meters. And an imbalance can only be detected with excessive meter readings on a single phase. Right now we are sitting with a R15mil Eskom bil for the month. I have helped the Chief a couple of times with some Calculations.

I never read the post in question that way at all, I read it that PFC is mainly used by large 3 phase industrial users in part due to how they are billed.

 

[Magnum]

I never read the post in question that way at all, I read it that PFC is mainly used by large 3 phase industrial users in part due to how they are billed.

It's a double misconception. Not everyone with 3 phase has special meters. And not only 3 phase pays extra.

 

[Tacet]

Personally I don't see the need for PFC in a solar setting unless your PF is worse than the rating of your inverter, which I don't think is very likely.

Reason:
Your inverter's kW rating is basically the amount of power it can convert from DC to AC. It is the active/true part of the power consumption. You can't change that.
Your inverter's kVA rating is determined mainly by the wire gauge of its transformer gauge and is the apparent power, which consists of both the active and the reactive power. It is an indication of how bad a PF it can handle. Fixing a bad PF will decrease the reactive component of the power consumption, but it won't do anything to the true power used.

Example:
If the apparent power is 2000 kVA, 2886 A for a PF 0.8 circuit, the true power will be 1600 kW (2309 A) and the reactive power will be 1200 kVAR. Making the PF unity will result in the reactive power being nil, and the apparent power being 1600 kVA, 2309 A. Your saving is in decreasing the current in the system, not in true power. Where PF plays a role in residential installations is where the power meter measures current. In that case you pay for the apparent power, not the true power.

 

[Kawak]

Personally I don't see the need for PFC in a solar setting unless your PF is worse than the rating of your inverter, which I don't think is very likely.

Reason:
Your inverter's kW rating is basically the amount of power it can convert from DC to AC. It is the active/true part of the power consumption. You can't change that.
Your inverter's kVA rating is determined mainly by the wire gauge of its transformer gauge and is the apparent power, which consists of both the active and the reactive power. It is an indication of how bad a PF it can handle. Fixing a bad PF will decrease the reactive component of the power consumption, but it won't do anything to the true power used.

Example:
If the apparent power is 2000 kVA, 2886 A for a PF 0.8 circuit, the true power will be 1600 kW (2309 A) and the reactive power will be 1200 kVAR. Making the PF unity will result in the reactive power being nil, and the apparent power being 1600 kVA, 2309 A. Your saving is in decreasing the current in the system, not in true power. Where PF plays a role in residential installations is where the power meter measures current. In that case you pay for the apparent power, not the true power.

In the above case, can I assume the savings in amps will translate to my battery bank? Or is the savings "phantom" and really only matters to equipment damage and wiring "heat" not "real" energy? This just came to me in the thread as one less battery in the bank is a savings of over 20K for off grid solar.

 

[PaulMurkin]

Wanted to find out if anyone is using power factor correction on their solar inverter/generator setup, does it do anything?

My understanding is it will bring the KW closer to the KVA rating of these machines, but does it actually make any difference in real life? Do those tiny units sold online actually work? They seem to just have a small capacitor in them.

Snake oil

 

[Tacet]

In the above case, can I assume the savings in amps will translate to my battery bank? Or is the savings "phantom" and really only matters to equipment damage and wiring "heat" not "real" energy? This just came to me in the thread as one less battery in the bank is a savings of over 20K for off grid solar.

It will not translate to your battery bank.

 

[PaulMurkin]

Good read, though my non electrician brain still don't really know why it happens, it feels like motors are designed wrong to need something that is out of phase to power itself, makes sense that correcting it saves energy. Will the saving equate to actually using less of my battery if I ever go off grid? Will going off grid make PFC worthwhile for a home install?

The answer is simple...
AC motor is inductive. To make it operate on single phase, you need to introduce a phase shift between two windings which creates the rotating magnetic field in the stator coil that turns the rotor.

Inductive loads cause the current to lead the voltage by 90 degrees. Capacitive loads cause the current to lag by 90 degrees.

At the domestic level, a notorious cause of poor power factor is the non-linear load, aka SWITCHING POWER SUPPLY. But I've yet to see a case where this has ever been an issue. Sure, its mandated to have active PFC in power supplies above a certain wattage to qualify for the CE mark, but even so, never seen or experienced any real problems.

The inline filter between the inlet and the power supply is usually sufficient.

I've only ever had to deal with PFC at a big factory, that used many thousands of kVA 3 phase, a whole shop full of lathes, mills, etc.. huge place

 

[Geoff.D]

The motor that I know acts this way is my pressure boosting pump which I can hear from the kitchen and begins to sound like it's seriously low on power, any way to test if capacitor is dying? Or maybe I can just change it, local shop sells the capacitor for just R110.

1. The fact the local shop sells spare capacitors, says to me it is a known failure point for that specific make of pressure pump.
2. Inspection is usually the first step to see if the capacitor is failing ( bulges, leaks, popped seams etc).
3. You can use a capacitor tester to verify the value.

If you do decide to replace it, first check the spec of the capacitor, especially its voltage ratings and try and get a higher rated one instead.

 

[Neuk_]

They are

Thanks, interesting.

 

[Kawak]

1. The fact the local shop sells spare capacitors, says to me it is a known failure point for that specific make of pressure pump.
2. Inspection is usually the first step to see if the capacitor is failing ( bulges, leaks, popped seams etc).
3. You can use a capacitor tester to verify the value.

If you do decide to replace it, first check the spec of the capacitor, especially its voltage ratings and try and get a higher rated one instead.

Thanks for the advice, will ask for that.

 

[Kawak]

@fragtion thank you, you are likely correct, I have now ran the system on battery only for 3 consecutive days and it's been perfect, no flicker or strange noises on any of the pumps. Guessing Eskom doesn't really have enough power so we need ripple control?

@Geoff.D changed my capacitor just because it looked old and wasn't an expensive exercise, my original one was marked 400V 25uf, bought a larger one, 500v 30uf, price difference was only R8, works fine, thanks.