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Topic Title: Problem with volt drop on UKPN supply
Topic Summary: I say voltage too low they say not
Created On: 07 December 2018 03:07 PM
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 07 December 2018 03:07 PM
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505diff

Posts: 182
Joined: 20 March 2006

Hi folks, I've got a customer who has rented a farm unit and used it as a joinery shop for about 9 years the supply is 60/80 amp three phase underground service, from a pole mounted transformer about 200m away, the transformer also supplies a farm house via an underground supply, these are the only buildings off the transformer.

The supply is also sub metered to a a joining unit that has been up to now used as storage, however now a car alarm installation company have the unit, the loading on this is low with no car ramps or air con units and at the time just one 2kw panel heater. The lighting in the car workshop are low bays.

The problem is when my customer starts up a planing machine the low bays go out and some of the fluorescent tubes dim.

I want to look at this about 8 weeks ago and found that even when a small chop saw that a chippy would use of site was started the lights flickered.

My first thought was a loose connection, but due to the fact I could not isolate much at the time I tired another method which was to go into the farm house and test the voltage as loads were added in the work shop, my MFT which is in calibration registered 197 volts with a 45amp load across three phases in the workshop, the load without any machines running is 20amp per phase, remember this is a separate service off the same transformer.


I then at the joinery shop incomer carried out a loop test which was all fine.

The motor that seems to cause the problems has a 6 kw start up current which is a bit of a spike but not massive, even without this the voltage heads south with every another thing is switched on.

UKPN were called in and fitted logging equipment at the service head, the customer told me after a week they returned and found it was not working as it had been installed incorrectly, it was then refitted and they seem to think its within the limits it should be.

I'm intending to return with a number of heaters and my spare testers to double check the voltage to load it up to about 50 amps per phase.

Naturally the transformer is in the usual asset managed condition, in a field on a pole leaning at 40 degrees is stained black around the bushings with oil that's run down it, also the customer told me two lv fuse holders burn out in the last five years one causing a small fire.

I don't know the rating of the TX but its the biggest you could fit on a single pole.

UKPN have told the customer he needs to pay for a supply upgrade which i think is totally unnecessary, what do you think?
 07 December 2018 03:33 PM
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OMS

Posts: 22864
Joined: 23 March 2004

What's the agreed supply capacity ?

It might be fairly low and the basically the user is causing his own problems

70 kVA through a small pole pig transformer and 200m of run is inevitably going to create what might be described as a voltage depression

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 07 December 2018 03:37 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

Voltage drop within the consumers premises, including any sub-metering, is not the fault of the DNO.

If however the steady voltage at the meter is below that permitted then I believe that the DNO must rectify this.
AFAIK they only need to deal with a persistently low supply voltage and are not liable for dips during motor starting etc.

The lower limit at the point of supply is 230 volts less 6%, or 216 volts.
Voltage drop within the consumers premises should not in most cases exceed 5%.

The only wiggle room that I can see would be for the DNO to claim that the customer is overloading the supply.
The "agreed supply capacity" MIGHT be less than that implied by the size of the cut out fuses.

It might be worth fitting LED high bay lights, many types are ok down to 100 volts.
 07 December 2018 05:55 PM
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Weirdbeard2

Posts: 753
Joined: 29 November 2017

Hi 505, if the problem is the low bay lights going off and then not coming back on for a while as they won't restrike until cooled a bit, how about replacing the lights with LEDs?
 07 December 2018 06:17 PM
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505diff

Posts: 182
Joined: 20 March 2006

Thanks for the replies just to confirm all readings have been taken within 1m of the cut out on each service not at the end of a sub main. I don't know what the agreed supply is on site, but i've got another customer with a single phase 60 amp supply with a good 100m run and this often gets fully loaded and that pole mount tx is something like 16kva and they never have any problems. The car workshop are now fitting low bay LEDs. I think at some point we in the past the farmer had a grain dryer on site, hence why I think something may be a miss, if you loaded a 60/80amp household single phase supply to full load you would not expect the lights to dim!
 07 December 2018 06:38 PM
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chrispearson

Posts: 1095
Joined: 15 February 2018

Originally posted by: 505diff

I don't know the rating of the TX but its the biggest you could fit on a single pole.

UKPN have told the customer he needs to pay for a supply upgrade which i think is totally unnecessary, what do you think?


... but i've got another customer with a single phase 60 amp supply with a good 100m run and this often gets fully loaded and that pole mount tx is something like 16kva and they never have any problems.


I suggest that you get your wellies on and have a shufti through a pair of binoculars and let us know the rating of the Tx.
 07 December 2018 07:00 PM
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perspicacious

Posts: 8055
Joined: 18 April 2006

What is the ASC and what disturbing loads were declared?

Regards

BOD
 07 December 2018 07:09 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

Originally posted by: 505diff

Thanks for the replies just to confirm all readings have been taken within 1m of the cut out on each service not at the end of a sub main. I don't know what the agreed supply is on site, but i've got another customer with a single phase 60 amp supply with a good 100m run and this often gets fully loaded and that pole mount tx is something like 16kva and they never have any problems. The car workshop are now fitting low bay LEDs. I think at some point we in the past the farmer had a grain dryer on site, hence why I think something may be a miss, if you loaded a 60/80amp household single phase supply to full load you would not expect the lights to dim!


Under 200 volts, close to the cutout is too low, unless the load is in excess of the agreed supply capacity.

If I fully loaded a domestic supply I would expect the lights to dim a bit, but not to below 216 volts at the cutout, and hopefully not below 200 volts at the point of use.

Regarding the presumed previous grain dryer, I suspect that this was an oil burning unit. These have a typical electrical load of from about 6Kw to 20Kw, for fans, controls, pumps, and augurs to move the grain.
An electrically heated grain dryer can be much more than that. The last one that I saw was just over 200 amps per phase !

Drifting a little O/T, but back in the good old days I knew someone who had "summer bulbs" and "winter bulbs" for the most used lights in their rural home.
The winter ones were 210 volt and the summer ones 240 volt.
 07 December 2018 08:08 PM
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kellyselectric

Posts: 497
Joined: 22 July 2016

If the LV fuses burnt up and caused a problem I think Ide be inclined to ask the DNO to check the joints up their also I wonder if there mite just be a faulty underground joint. Also if it was me I think I would check the phase to earth volts and see if they are much different from phase to neutral volts
 08 December 2018 09:38 AM
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KFH

Posts: 799
Joined: 06 November 2010

While working at a domestic customers (urban environment) I recorded a steady 190V at 6:00 in the evening. I had checked the Ze and PFC earlier, can't remember figures, and there were no issues apparent that would have caused a low voltage. The customer said that cooking Christmas dinner took forever and normally cooking in the evening was slow. I told them to phone their supplier which they did and were effectively told its not our problem! I suggested they talk to their neighbours to see if they had a problem but heard no more.
 08 December 2018 10:05 AM
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Zoomup

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Joined: 20 February 2014

Gas oven.

Z.
 08 December 2018 10:16 AM
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AncientMariner

Posts: 904
Joined: 14 December 2004

If I wanted to find out the Agreed Supply Capacity (ASC) say for a house built in the late 1950s, would the DNO be able to advise? The cut-out fuse is 80 amp - fitted by the DNO's jointer when the cut-out was moved in 2002.
Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 08 December 2018 10:44 AM
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broadgage

Posts: 3170
Joined: 07 August 2007

What would the DNO do if a customer had an agreed supply capacity of 23 KVA on a 100 amp fuse, and actually used 23 Kva but with the voltage of about 190 volts ?

That would represent a line current of about 120 amps and would cook the fuse and eventually operate it.
The customer could reasonably argue that they are NOT overloading the supply "your agreement says 23 Kva, and we are using 23 Kva"
 08 December 2018 10:51 AM
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mapj1

Posts: 12039
Joined: 22 July 2004

The DNO certainly 'ought to know' the supply rating , though in reality there may be a few cases where they have to send some one to have a look so they can remember.

For the OP, if its an old TX it is probably sized assuming 240V rather than 230, so it will set off at more like 250 unloaded. To lose 20% on the route presumably something is working rather harder than intended. Has the paint blistered off it?
Can you measure PSSC ? We can probably infer something about supply impedance.
The cheap solution to the lights is probably automatic voltage regulation for that circuit.

-------------------------
regards Mike
 08 December 2018 06:56 PM
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kellyselectric

Posts: 497
Joined: 22 July 2016

KFH how can the DNO say its not their problem? Its theirs tranny that is supplying the house after all. I find its a really bad and hard to understand attitude. Especially silly bearing in mind how precious they are about their intake fuses
 08 December 2018 07:58 PM
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MHRestorations

Posts: 83
Joined: 22 October 2017

With DNO's (at least SSEN) it seems to be the luck of the draw whether you get a decent normal human being who will say 'yeah that's not right, we'll look into it', or a jobsworth who complains that the 80A switchfuse we just installed because of moving the board to a new location is 'on our piece of chipboard' (i kid you not)
 08 December 2018 08:58 PM
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KFH

Posts: 799
Joined: 06 November 2010

Originally posted by: kellyselectric

KFH how can the DNO say its not their problem? Its theirs tranny that is supplying the house after all. I find its a really bad and hard to understand attitude. Especially silly bearing in mind how precious they are about their intake fuses


I didn't think they could and told the customer so. But they told me the answer while I was on the last job I did for them and I was up against various time constraints so could not make a call myself to try and push it further.
 09 December 2018 11:24 AM
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electric

Posts: 53
Joined: 04 June 2009

Hi KFH

Just a thought regarding the answer your customer received.

The Electricity Supply Industry can be rather confusing these days, as opposed to the time when if you had a query with anything relating to the your electricity account, meter, or the distribution network, you just contacted your local "Electricity Board" who would deal with it.

If your customer did contact their "Electricity Supplier", then the supplier was correct in the answer they gave, but could/should have been a bit more helpful in informing the customer who to contact.

Voltage complaints relating to the Public Electricity Distribution Network are the responsibility of the customer's DNO (Distribution Network Operator) or IDNO (Independent Distribution Network Operator), not their Electricity supplier.
Even if the DNO and the Electricity Supplier are both part of the same company, regulation dictates they operate separately.

Kind regards
Chris

-------------------------
Kind regards, Chris
 13 December 2018 12:58 PM
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505diff

Posts: 182
Joined: 20 March 2006

A quick update, went back to site today, and retested and it seems a lot better, UKPN have removed the logging equipment and resealed the cutout but not blanked off the terminals which the equipment was connected to in the cut out (nice). I looked at the letter which they sent the customer and the graphs did not correspond any where near my original readings, I think something was loose and they have sorted it out, but they have not mentioned anything about faults. At least for now the problem seems to be sorted out, thanks for your input folks.
 13 December 2018 02:32 PM
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statter

Posts: 173
Joined: 06 February 2013

Hello Glad to hear you got this solved. For the future there is Guaranteed Standard that DNOs such as UKPN have to follow when they receive a voltage complaint from a customer. The details are in The Electricity (Standards of Performance) Regulations 2015 but basically they have 7 days to offer a visit or an explanation. If they don't offer a visit within 7 days or turn up on the arranged day they have to pay the customer £30.

This is one of several Guaranteed Standards that DNOs have to stick to.


Peter
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