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Topic Title: High incoming voltage
Topic Summary: Fllodlights not working
Created On: 03 November 2017 08:53 PM
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 03 November 2017 08:53 PM
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tillie

Posts: 891
Joined: 03 May 2006

Hi , I look after the electrical installation at a football stadium.

Came in on Monday morning and was asked to check out some 1000w lights that roll out over the pitch.

There are 72 lights on each rig and there are 3x rigs. (1000w MH each lamp )

About 1 in five lamps were out on each of the rigs.

Checked all supplies and found voltage to all points.

Checked ballasts and found that they have small warning lights on that were flashing.

Phoned manufacturers and have been informed that the flashing denotes overvoltage to the fitting.

Checked voltage and found that the lamps not working were receiving 459v across the phases ( 400v lamps ).

The lamps that were working were reading around 435v.

At this point I was able to unplug the lights and plug them in at the other end of the pitch where the supplies are fed from a different substation.

All the lights worked so I came to the conclusion that the voltage is too high for the fittings when fed from the other end.

These lights have been working perfectly for a number of years.

I then checked the voltage at the main distribution panel in the car park next to the suspected problem transformer and found voltage across phases to be around 460v and phases to neutral readings of 260v.

At what point does overvoltge become dangerous ?

I also checked some points around the stadium and even 300 mtrs away from the main panel I am reading 260v at plug sockets.

Could this also explain why fridges are packing up at an alarming rate ( 5 since the start of the season ).

We called out UKPN on Thursday and they have said the voltage is slightly high but within their spec.

They are going to see what they can do ( maybe ).

In the meantime we cannot use all the lights which is going to cause a problem.

Not too sure where to go from here.

Anybody have any pointers ?

Regards
 03 November 2017 09:58 PM
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MHRestorations

Posts: 40
Joined: 22 October 2017

off the top of my head, the voltage is 230 (400v phase to phase) plus minus 10%, so 253 absolute max, or 440 abs max phase to phase. This is way over that. UKPN are incorrect in saying it's within their limits. Their limits are as above, defined by statute. There's something wrong (possibly a stuck tap changer, or incorrect tappings on the one substation). But it's their issue to fix.

As to liability, IANAL
 03 November 2017 10:02 PM
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MHRestorations

Posts: 40
Joined: 22 October 2017

Adding to the former, anything above 246 or so, I get antsy....overvolting lowers the life of conventional tungsten lamps significantly, and other appliances can react ....poorly. As to actual danger, there shouldn't be any, the OCPDs should be fine with a 20or more percent overvoltage (from experience and pragmatism), and wiring is fine at 300/500v usually. So danger... notsomuch (rogue appliances aside). Inconvenience and stress.... (both to people and devices) are not so simple.
 03 November 2017 10:06 PM
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alancapon

Posts: 6914
Joined: 27 December 2005

Originally posted by: tillie
. . . I then checked the voltage at the main distribution panel in the car park next to the suspected problem transformer and found voltage across phases to be around 460v and phases to neutral readings of 260v. . .

. . . We called out UKPN on Thursday and they have said the voltage is slightly high but within their spec. . .

Rubbish. The statutory voltage limits for a phase to earth measurement are 216.2V to 253V, measured at the outgoing (load) terminals of the meter, or the isolator immediately following it. At 260V, they are in breach of the ESQCR regulations which their licence requires them to comply with and they must make the necessary adjustments to drop the voltage to 253V or lower.

Regards,

Alan.
 03 November 2017 10:26 PM
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tillie

Posts: 891
Joined: 03 May 2006

Hi , thanks for replies.

That was exactly as I thought ie 253v maximum.

Is this something they can fix quite easily ?

I actually measured the voltage with them present in the main switch room.

They went away to check out the local transformer and then phoned me and told me that it is slightly high and he has passed he's findings on to others and it is now out of he's hands.

I was given a job number but have heard no more.

My worry is that they are going to leave as is but thanks to your comments I think we have a case.

Regards
 03 November 2017 10:41 PM
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broadgage

Posts: 2432
Joined: 07 August 2007

I would double check that the instrument used is reading correctly, and presuming that it is in order then complain to the DNO.
The measured voltage is appreciably in excess of that permitted and the DNO should correct it.

Whilst high phase to neutral voltages can sometimes be due to a high resistance neutral within the consumers installation, that would not explain the high phase to phase voltages measured.

And yes a routinely high voltage can kill fridges, they seem more vulnerable than other appliances.
 03 November 2017 11:47 PM
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mapj1

Posts: 9553
Joined: 22 July 2004

Normally the substations have enough tapping options (connections part way along the windings) to allow them to fiddle it in excess of 10% either way.
Of course it may have been wound up to max because someone else at the other end of the line is complaining its a bit low for them.

Check your meter against one known to be calibrated, keep a diary of voltage readings as near as you can easily measure to the incomer and assuming it is regularly over 250 L-E , then keep ringing them back to remind them.
You might try and speed them up and threaten to bill them for the broken equipment.
A well known make of Italian fridges in particular are designed with 220V as design centre, and are already running warm at 240.
automatic voltage regualtors exist, but really should not be needed on a well installed set-up. One could get one sent over from our colleague in Bankok I suppose

-------------------------
regards Mike
 04 November 2017 08:35 AM
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tillie

Posts: 891
Joined: 03 May 2006

Hi , I have took readings with three different testers including my MFT which is calibrated.

There is also a dial on the main panelboard which allows me to test all phases to neutral and between phases.

All readings are above permitted.

Would a high resistance neutral downstream of the main panel raise the incoming neutral voltage ?

Regards
 04 November 2017 09:00 AM
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broadgage

Posts: 2432
Joined: 07 August 2007

A high resistance neutral, would under an unbalanced load, cause a reduced voltage on the highest loaded phase and a rise in the voltage on the least loaded phase.
The phase to phase voltage would remain unaltered.

A high resistance neutral within the customers installation should not noticeably alter voltages within the DNO network, up to and including the service cut out.
 04 November 2017 09:14 AM
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AncientMariner

Posts: 717
Joined: 14 December 2004

Originally posted by: tillie

Came in on Monday morning and was asked to check out some 1000w lights that roll out over the pitch.

There are 72 lights on each rig and there are 3x rigs. (1000w MH each lamp)


From your original post, that is quite a few kW in total and 72kW per phase.

When you and UKPN measured the voltage, was that off-load or with the operating lamps running?

I'm just curious as regards volt drop in the supply with that load and also how far away is the 11kV to 400V transformer?

Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 04 November 2017 09:34 AM
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tillie

Posts: 891
Joined: 03 May 2006

Hi , that was with the lamps running.

Even when the lamps are off the voltage remains the same roughly.

There is the transformer next door to the main panelboard with the main substation 2 miles away.

Regards
 04 November 2017 09:46 AM
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AncientMariner

Posts: 717
Joined: 14 December 2004

The "transformer next door to the main panelboard" is that 11kV to 400V (or as measured)? Is it owned by the DNO or the football club?

"The main substation 2 miles away "is that supplying 11kV to your next door transformer? (I'm guessing here that it is similar to one of two near here; one is 33/11kV the other is 132kV to 33kV and 33/11kV within the same site)

Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 04 November 2017 09:51 AM
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tillie

Posts: 891
Joined: 03 May 2006

Hi , it is owned by the DNO.

They told me they were going away to check the 33kva transformer which is 2 miles from the ground.

So not sure what the transformer next to the main panelboard is but assume 11KV TO 400V.

Regards
 04 November 2017 06:59 PM
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AncientMariner

Posts: 717
Joined: 14 December 2004

Would certainly seem to be a DNO, UKPN responsibility.

Please update the forum with the outcome etc.

Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 04 November 2017 10:48 PM
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alancapon

Posts: 6914
Joined: 27 December 2005

Originally posted by: tillie
. . . There is the transformer next door to the main panelboard . . .

The ESI standard transformers are 11kV / 433V on nominal tap, which will not help if you are right next to it.

Regards,

Alan.
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