Typical Domestic Power Factor?

[JohnW2]

As previously mentioned, I have recently had my electricity meter changed. What I now have is an Elster A1140, which E.ON appear to have programmed to provide only a very limited amount of information (in comparison with what it theoretically could provide). All that is currently available (for my E7 supply) appears to be total kWh, Day kWh, Night kWh and total kVArh. The first three are obviously straightforward (and correspond with what I’ve always had, but the last one represents information I have not previously had, so my curiosity has caused me to look at it!

Over the first few days, total kVArh has been running at about 28% of the total kWh figure. By my reckoning that means that kVAh = kWh x 1.0385, hence a Power Factor of about 0.96.

Is 0.96 a typical PF for a domestic installation? I think I was probably expecting ‘worse’. Very few of the loads in my house are likely to have a unity PF - although I suppose that most of the ‘large’ loads do. The only really ‘resistive’ loads are the heating elements in tumble dryer and immersions and (when used) electrical heaters, and the elements in (only very occasionally used) kettles, toasters, hair dryers etc. etc. Everything else (including nearly all of the lighting) involves motors and/or some sort of SMPSU (LEDs/CFLs, IT/other electronic equipment, chargers etc).

Kind Regards, John

 

[ericmark]

A good few years ago I got egg on my face when 20 x 60W fluorescent lamps tripped the 16A MCB on a 110 volt (63-0-63) supply. On getting a fitting on the bench I tried swapping the tapping from 110 volt to 127 volt and also removing the capacitor. The latter was quite a surprise, I expected the current used to go up, but not as much as it did. The 60W fitting could draw over one amp.

Now what then went through my mind is how do you know when a capacitor becomes disconnected or fails. Light output does not seem to alter, it just uses more power, with a factory we have a power factor correction unit which will correct the shift when the ones built in fail, but at home nothing.

So when I got an energy meter, plug in type, which showed the power factor I was interested to see what it showed. The old freezer was one item I looked at, 95% once running and I thought it would be so easy to include a capacitor just like with a fluorescent lamp.

But we also have devices which warp the sine wave, every time we turn AC to DC we rectify just the peak part of the wave form, so this must flatten off the wave form, every inverter drive we use, must warp that wave form more and more. Today by freezer, fridge/freezer and washing machine all use three phase motors and an inverter drive, the LED lamps are also all DC but not sure if there is any smoothing of the DC, and TV, Radio and all other electronic goods are DC. So the wave form must be warped.

Add to that DC generators with DC to AC inverters these also are unlikely to produce a true sine wave, although they could enhance the peak if they want to.

So I worked out the saving by fitting a capacitor to a freezer, however the result was just not worth doing, I did write a program in java script to use the info from the plug in energy meter to show what size capacitor to fit, but when I saw how little it saved, I never bothered fitting any.

 

[JohnW2]

Interesting stories, eric, but what do you think my 'overall' ('average', if you like) PF? Do you think it's typical of what one might expect in a domestic installation?

Kind Regards, John

 

[ban-all-sheds]

Is 0.96 a typical PF for a domestic installation? I think I was probably expecting ‘worse’.

Would you like to borrow my old oil-filled welder? I'm sure we could get closer to your expectations....

 

[JohnW2]

Would you like to borrow my old oil-filled welder? I'm sure we could get closer to your expectations....

So do you think that 0.96 is 'as expected' (without a welder)?

Kind Regards, John

 

[ban-all-sheds]

IHNI. You said you were expecting worse - I thought a socking great transformer might help make it worse...

 

[JohnW2]

IHNI. You said you were expecting worse - I thought a socking great transformer might help make it worse...

"Expecting" and "wanting" are not quite the same thing!

Kind Regards, John

 

[endecotp]

Some of your larger switch-mode power supplies may have power factor correction.

 

[JohnW2]

Some of your larger switch-mode power supplies may have power factor correction.

Indeed - and I guess that would probably relate to ones in computers and related equipment. However, many/most of them are pretty old, so I'm not so sure how likely it is that they will have reasonable correction. I have a plug-in meter which would enable me to check items individually, which I may do when I have some spare moments.

Kind Regards, John

 

[AdrianUK]

Do you think its 0.96 leading or lagging??

Over the last few years I've noticed that our home pf has slowly flipped to leading. As I write the draw is 1.384Kw, - 489VAr with a pf of 0.94 cap. It moves much closer to unity when the immersion cuts in.

The loads that I know are running are: 4 desktop PC with LCD monitors, twin 5' fluorescent lamp, twin 4' fluorescent lamp and around 6 or so LED lamps, plus the usual SKY boxes, networking kit etc. The load is predominately SMPS (born out by the fact that our current THD is around 32% with around 20% being 3rd order - the current waveform has a very pronounced peak around the crest).

These figures are not coming from our DNO electric meter but from the ISKRA MC750 measurement Centre that is connected into the outgoing meter tails

 

[winston1]

Now what then went through my mind is how do you know when a capacitor becomes disconnected or fails. Light output does not seem to alter, it just uses more power,

Er, no. A capacitor is a zero power factor load. Disconnecting it will not make the light use more power. More current will flow at a lower power factor, but the power will be the same.

 

[JohnW2]

Do you think its 0.96 leading or lagging??

As I implied in my OP, other than for the motors of fridge/freezer compressors, WM, DW & dryer and CH pumps etc. (when they are running), I would imagine that most of my non-resistive loads (and virtually all of them which are on for long periods, or 24/7) are capacitive, being as they involve SMPSUs of one sort or other, with or without filter capacitors. The only fluorescents left with inductive 'ballasts' are very rarely used.

Over the last few years I've noticed that our home pf has slowly flipped to leading. As I write the draw is 1.384Kw, - 489VAr with a pf of 0.94 cap. It moves much closer to unity when the immersion cuts in.

Not all that dissimilar from mine, then.

Kind Regards, John