ECN Forum Forums General Topics of the Trade General Discussion Area Faulty kWh meters

to WFO

Average time from datalogging experience on houses is that the Ave load is around 2 Amps for 20 hrs / day The other 4 hours it can be anything from 2.1 up to 60 Amps.

In general I would conclude that the Ave error is probably around the 3 to 4 % mark which is not too bad cosidering those meters were 70 + years old. The higher loads > 30 Amps are usually drawn around cooking times when ranges and hotwater demands are higher. Winters in Auckland are not that cold and maybe over a 2 month period some form of electric heating is needed to keep the houses warmer and dryer.

Some shorted turns in the current coil counteracted the increase in speed of the disc too.

Remedie: Probably 99 % of these meter have been replaced by now. There might be the odd one around. Because they had cyclo type dials the meter readers didn't complain too much. Usually these were in the old homestaed houses , sometimes on a marble switchboard high up in the dark corners of the hall.

I gor one in my collection and will post a piccie, and ask one of the moderators to insert it.

2 pictures as promised by RODALCO:







BTW Ray, we've still got a lot of them Ferranti's down here, but they aren't quite that old.
Be a while before we get anything electronic here as far as metering goes, we've only just finished installing all the ABB ripple control relays.

Thanks Trumpy for posting the piccies.

Nothing is more reliable long term than the ferraris disc meter, Accuracy wise also they are the best meter available as far as I'm concerned.

Unless you are brainwashed by sales talk what all these electronic meters can do besides recording power usage.

Man, you sure got your money's worth out of them!

I know what you mean about the electronic meters. They'll probably get better, but I'm a little leary about them still. I had one of the meter manufacturers tell me, "Sure, electronic meters are more accurate and have morre features.....but face it. You'll be lucky to get 15 years out of one."

Considering they already cost 3 to 4 times as much, that's not very comforting.

But here's why you'll see them. Deregulation
(or "Re-regulation" as we call it here in Texas) is raising another part of its ugly head. The U.S. Energy Act of 2005 is trying to force everyone to offer TOU (time of use)metering or some equivalent form to all customers within the next two years.
Unfortunately, you just can't get that kind of data from the older disk meters.

[This message has been edited by WFO (edited 12-27-2005).]

Hey, with all the talk about 'standby' power consumption in electronics and how they collectively suck up precious hydro over the long run, how much consumption does the actual meter use and add to the power users bill?

I just had a case where the homeowner was complaining about excessive billing for the 2 years they were in the house. Utility changed out meter once...no change in bills and they told him removed meter was OK. A smoked HVAC fan motor prompted a call to an electrician who discovered a line-to-neutral imbalance of voltage...like 90-130 or so at the moment. Classic open/bad neutral situation although the homeowner hasn't noticed the other symptoms such as dim/bright lights, etc. Electrician contacts the utility who comes out and does a lot of work. Problem solved...bills down to what the homeowner thinks is reasonable. Now, I am told that the typical Form meter used in single phase 3 wire residential applications is non-Blondel compliant and reads all line-neutral usage at 1/2 the current and twice the voltage. Therefore, an imbalance in line voltages will undermeter some loads and overmeter others...the net effect depends on the load distribution and the imbalance. 240 volt loads will always be metered correctly. Anyone ever heard of this effect?

You are correct.

Each current element of a form 2 meter is designed to produce 1/2 the flux proportionate to the current going through it. The left hand half of the element being wound opposite to the right hand element. And, as you mentioned, the potential coil is connected across each leg (240 volts).
If a 120 v load is pulling "A" amount of current (and for simplicity assuming Watts = Volts x Amps and ignore PF), then 240 x 1/2 A = Watts.

Which of course, is the same as 120 x A = Watts.

For a 240 volt load, the "A" current is returning in the other leg of the meter current coil in the opposite direction. But since the coil is wound in reverse, the flux fields "coming and going" are cumulative.

So 240 volts x (1/2 A + 1/2 A) = Watts.

Which of course, is the same as 240 x A = Watts.

So take an unbalanced load....100 amps on one leg and 10 on the other; and assume a 4 volt drop in the service wire on the heavier loaded leg.

Actual watts,
(116 volts x 100 amps)+(120 volts x 10 amps)=12800 watts or 12.8 Kw.

The meter sees,
236 volts x (1/2 of 100 amps + 1/2 of 10 amps) = 12980 or 12.98 Kw

Or a 1.4% overcharge (if I did my math right). It pays to be balanced for more than voltage drop. Of course, I'm just grabbing arbitrary values at random here.

Hey RODALCO...how about checking my math. Did I blow it?



[This message has been edited by WFO (edited 12-27-2005).]

Your maths look right there WFO.

Under these very unbalanced conditions that meter still does a very good job considering that a class 2 meter is allowed a ± 2.5 % error and is well within its specs.

In general the bit over and under measurements will cancell each other out longer term.

In case of broken neutrals there are usually a lot of problems with blowing lightbulbs if exposed to a high voltage for too long or appliances not working properly.

HAPPY NEW YEAR !! Ray.

Is that also true for electronic meters?

I recently used Hager electronic meters in the tenancies of a shopping centre. One tenant managed to reduce his bill considerably by changing the C/T ratio setting. It didn't occur to me when I selected them that there was nothing stopping anyone from doing so.

Were these direct reading electronic meters or did they have a multiplier attached ?