Power factor and domestic electricity billing in the UK?

[Uncle Peter]

Can someone confirm that power factor is NOT taken into consideration for domestic supplies? I have a feeling it isn't, but I can't find any information on the internet. If it matters, it's a modern (

[John Rumm]

Domestic meters only record real power...

[harryagain]

The very fact that you pay for kilowatt hours (Kwh) not kilovoltamps hours (Kvah) tells you that power factor is not accounted for. Only commercial organisations might be asked to pay for Kvah.

[Brian Gaff]

So how does this affect actual loading of the system. Is it large enough for them to really be losing out? I can remember that when I worked in a factory, the leccy board came around and wanted to redistribute the soak test racks and other things to different mains phases due to imbalance of power factor due to the method the ssets used to get power. It always made me wonder how, if this was so bad, why it made no difference when they wer in peoples homes. Brian

[John Rumm]

For industrial users, certainly...

Domestic users are far less likely to have a PF significantly below unity, and if they do, it tends to be down to harmonic content rather than classical voltage current phase mismatch.

[Uncle Peter]

I know they call it kWh, but that doesn't mean that's what they charge for :-)

I wanted to make sure that what my own meters read was the same as what theirs does. My own meters show power factor, but I think the price they show is not based on that reading. It's not clear though, as one of them (newer version of the same model!!) shows kW as kW, but the other shows kW when it's actually reading kVA. For example, one might read 240V, 2A, 480W, PF 0.7. The other will read 240V, 2A, 336W, PF 0.7. I think when I watched the costs going up on the counters, they both seemed to be calculating cost from VxAxPF, despite what was shown as "kW".

[Uncle Peter]

I would imagine that in a street, the substation is even loaded as there are several houses on each phase. Also capacitive loads and inductive loads probably even out too. But the square-wave-creating switched mode power supplies cannot be evened out, so I guess that's costing them in losses in wires.

[PeterC]

At work (25 years ago) we paid for kWh but were charged for MD (Maximum Demand) peak on kVA (not kVAh). Much correcting of PF went on; especially as, being design and manufacture of electronic assemblies, the load was mostly fluorescent lighting and not a lot of inductive load.

[harryagain]

The power factor is the ratio between true power (Watts) and Apparent power (Volts x Amps) The current lags the volts in inductuve equipment. The power factor is also the cosine of the angle between volts and amps. So angle = 0, cos 0=1 (ie in phase, (resistive load) Power factor is

1/unity.

angle = 90, cos 90 = 0 (pure inductive load) Nor actually achievable in practice.

[dr.s.lartius]

domestic supplies? I have a feeling it isn't, but I can't find any inform ation on the internet. If it matters, it's a modern (

[harryagain]

Volts x Amps x power factor IS watts by definition.

Power factor IS the ratio between watts and VoltsxAmps.

Watts/voltsxamps = Power Factor.

[Windmill]

But an old coin meter installed by the husband of a relative in the boarding house he used to run charged for an inductive load. Quite generously.

As I found out on a trip back to Scotland while still living in Canada.

I had plugged in a 3.5 KW autotransformer (needed 'cos I planned to use

110V power tools as soon as tenants left a flat which I'd rented out).

With no transformer load to speak of, the meter needed repeated feeding!

It now has a 10uF 250VAC capacitor to correct the power factor (also stops it from tripping MCBs during power on).

[John Rumm]

True, but not usually that applicable to non unity domestic loads in this day and age...

[Uncle Peter]

I worked in a school which had a capacitor bank. Not sure why, I can't see most of their loads being inductive. Maybe it was from back when they had inductive ballasts on the lighting. Probably nobody thought to check if it's still set right.

[Uncle Peter]

[Uncle Peter]

Yes, I know. So one of my meters is incorrect (I think it's just the kW display is actually showing kVA, calculating the cost seems correct - based on kW, not kVA). This one: 240V, 2A, 480W, PF 0.7.

[harryagain]

There are both three phase and single phase transformers. Large load usually have three phases in order to distribut the load equally over the phases as far as is possible.

The high voltage side is isolated from the low voltage side.

The naming/colouring of the phases is purely arbitary, only the "rotation" of the phases is important.

If a load is unbalanced (ie not equally distrtributed between the phases, it results in both phase shifts and unequal voltages appearing between phases.

[Andrew Gabriel]

Yes. They generate 3rd-harmonic distortion, which can be bad in large quantities because it adds together in the neutral line, rather than canceling out between phases.

The final step-down transformer is a delta-star configuration, as there are no neutral conductors in the supply network until you step down to

240V. A high load on one of the 240V phases becomes a not so high load on two of the three phases supplying the final stepdown transformer, so you can see that your one-phase load is already being smoothed as you work back up the supply chain.

[Uncle Peter]

And I guess there's no way to cancel a harmonic like you can shift normal PF with a capacitor.

I see. So the only problem of uneven phase loading is locally.

[The Natural Philosopher]

Not here it ain't. Nor any of the pole mounted transformers on the local

11KV overheads. One phase partial deltas.

Star-delta is not a configurations that exists in the real world either. Its one or the other.

Its hard to see how you can supply a single phase from three phases anyway. A single phase is always the result of the difference between two phases.

You cant extract a single phase from a star connection anyway. A star connected load implicitly is a three phase load.

as there