STRANGE NEUTRAL CURRENT !!!!

[simon rogers]

Morning fellow practicioners of the dark art we call ELEKTRICKARY , I have recently been ask by a close freind if i thought his electric bill seemed "A SLIGHTLY BIT HIGH!!!". So he showed me it and I nearly fell off my bar stool (forgot to say he is a publican),his usage breakdown has come back at 269KWH now wait for it ..........per day . Now i admit i am no expert on metering rates etc , but i am 47 and started my apprenticeship when i was 16 , so have a few years under my belt , have been self employed from 21 till now and have run / designed/tested jobs from an extra socket to 20/30 million £ new builds and refits. So i am throwing myself out there to see if i am missing something bloody stupid . I have calculated his total load from fridges etc info plates lights by counting and added about another 30A on top , and it comes to 119A total . Now this is spread over a 415V 3 phase supply , which i have clamp metered up and monitered the indivdual cores which average out Brown/red- 23A , black/yellow- 19A & Grey/blue - 42A , oh and the neutral comes back with 38A on it.This obviuosly is nowhere near 269KWH , and was thinking this rouge N current must be from a dodgy connection on supply side ? It is also obviously a potential overheating risk i would have thought ? So does anyone have any thoughts to help me out PLEASE . thanks for reading my bumbbling thought train Simon

 

[Deleted member 26818]

As far as I am aware, meters do not measure neutral current.

 

[telectrix]

from the phase currents you quoted, the N current should be approx. 20A for that unbalanced load.

also,from another thread, it appears that your customer is billed on the phase with the highest current, i.e. 42A in this case.

 

[marc8]

from the phase currents you quoted, the N current should be approx. 20A for that unbalanced load.

also,from another thread, it appears that your customer is billed on the phase with the highest current, i.e. 42A in this case.

could you look at balancing the load slightly better this would then bring down the current on the highest phase & bring the other phases closer overall thus reducing the bill.

 

[The Ghost]

Is this an HH meter with remote monitoring. You have looked at his bills does it give a Kva figure on the top right corner?

 

[static zap]

Neutral currents are bad for the Bill ! ,
unbalanced , effectively paying for what you may not have used on 2 phases ,
(that' s the part of 3 PHASE that is a big down side)
....Has something got a bad power factor ?
Hence phases not cancelling as well as they should .
( Do they have propper central heating ? )

 

[The Ghost]

So the neutral is the overflow from the unbalanced phases. If I do a scaled triangle to get the neutral overload I get 30a on the neutral.

 

[UNG]

Have you looked back through the billing history and how it has changed over the last few months / years
Looking at the figures you have posted has someone got a decimal point in the wrong place or added a zero and it should really be 26.9KWH per day

 

[Wilko]

May have misunderstood, but 11kW continuously for 24hrs is 264kWh used. On a single phase 11kW is about 48A. So - is the load you measured continuous? I'd have thought it would average to maybe 10% of peak, perhaps. Which puts me back thinking @UNG is onto something

 

[simon rogers]

ok i will start answering from top down lol .Spinlondon a clamp meter will measure the current(if any) on anything you clamp it round. Telectrix not sure about the 20A and i think it depends on who and what tarrif it is on for billing .marc8 balancing the loads is my next step , not as easy as it should be due to nothing on the 30 way ancient ryfield board being labeled and multiple circuits coming out of at least half the fuses that are being/not being used.Vortigern not a HH meter just normal clamp meter monitered and recorded twice an hour for a day just to get an idea and didnt notice kva.UNG he is only in there a few months and the previous landlord hadnt paid any electric bills for god knows how long (about£ 34k long ) so no bills to compare it too ,but i had thought about the decimal point being wrong , its easily done if someone aint paying attention . Thanks all of you for the input and quick responces . I will hit it again later on and keep all of you posted to how it goes cheers sibo08

 

[static zap]

So the neutral is the overflow from the unbalanced phases. If I do a scaled triangle to get the neutral overload I get 30a on the neutral.

Using your 30 A graphically obtained , I get worst case 331kWh ... daily
(if exactly 2 phases -unused ...power factor may improve this !)
...2/3 of your bill is un-real (and i/j-joke) ...or NOT £
(my maths was lazy for- this one -interaction will probably make it 270)

 

[Simonslimline]

Any harmonics summing in the neutral?

 

[static zap]

...or it's just a pub full of old in-efficient things
old coolers / Halogen lighting , and electic heaters flat/accomodation
.. from era when electicity was cheap .... Breweries -are not generous !
Only need 16A per phase average to get there !
(got rid of old freezer -for this type of reason)

 

[The Ghost]

No harmonics on my part that is a straight equilateral calc/diagram

 

[buzzlightyear]

probably a faulty meter .on three phases. time to get DNO involved.

 

[FatAlan]

Anyone growing whacky baccy in the loft?

 

[David Prosser]

Old landlord didn't pay the bills ? Maybe trying to claw back some money from your mate. I've two ridiculously high bills in the past both of which were just a ruse to get me to ring the supplier and confirm details and to let them send a meter reader around. One was explained as they didn't believe the meter readings could be so low. It was a local cricket club that was hardly used through the winter. The other one was over a rented property where the previous tenant had skipped out without paying the last year or so electric. Two visits from the meter guys and new bills where issued.

 

[Lucien Nunes]

There seem to be some misunderstandings going on here. Ordinary meters measure energy used. They do not care which phase it is used from, or how well balanced the load is. You can use it all on one phase, or equally across three, the energy consumption will be what it is. They cannot charge you for energy you could have used on the other phases had they been loaded to the same current as the highest-loaded phase. The tariff might depend on your maximum demand, and half-hourly metering can report this, so there could be an incentive to manage the load both as far as size and timing of load peaks. That is reasonable and sensible, as spreading peak loads helps manage the energy networks.

Unbalanced loads create neutral current, as do certain harmonics in both single and 3-phase loads. Neutral currents themselves are of minimal importance to the customer, e.g. with a 100A TP+N supply it matters little whether the neutral current is 1A or 100A. There is a modest efficiency advantage for the supplier of the load is balanced due to lower cables losses, and they must manage the total neutral current so that it is not excessive in any distribution cable. But neutral current does not equate to 'energy paid for but unused' or any such thing. It's merely the algebraic difference between the line currents. If loads on different phases differ in power factor (e.g. lighting mainly on one phase, motors on another) then the neutral current calculations must take this into account. The most extreme cases, with phase angle controlled loads, can result in higher neutral current that any line current which can cause overheated neutrals, but this is truly rare and extreme. With the figures in the OP, there is no such hazard as the neutral current is less than the highest line, hence no reason to think something is going to be overloaded.

Low power factor causes higher currents than are truly necessary to deliver the amount of energy purchased. This increases cable and transformer losses, and hence costs the supplier, so there are incentives to keep the p.f. as high as possible. Again, this is a networks efficiency consideration, and while low metered p.f. might be reflected in a less favourable supply tariff, the supplier cannot charge for energy that would have been delivered at the same current had the p.f. been unity.

Going back to the OP, 269kWh per day is an average load of 11kW. I can produce that load by switching on the appliances I can see from where I am sitting, and that doesn't include any cooking equipment. It could result from being wasteful, growing tropical plants, even a miscalibrated meter. But it doesn't sound like anything that would make me fall off a bar stool or an indication there is anything amiss with the supply.

 

[static zap]

....... The tariff might depend on your maximum demand, and half-hourly metering can report this.............

So a high startup demand , may get you on less reasonable price per unit , or is it more of a equipment standing charge -=un-used capacity in hardware ?
(had heard about staggering run up of high demand
devices so the don't coincide)
Was penalty for a peak current , or power consumed ?
(or is this in-consistent across DNO / metering fitted)

 

[Marvo]

If his bill is in units of kWh then he's not being penalised for poor power factor, non-linear loads, harmonics etc and as Lucien says I've never seen a metering device that calculates consumption using the highest load phase current.....