Too Many Volts

[awemawson]

When we moved here eight years ago, I was aware that the mains voltage was quite high. Not really surprising, as we are supplied overhead by an 11kV three phase line, and the step down transformer to 415v three phase / 240v single phase is on our land.

This means that we are at the feed end of the cable, so if they are to allow for voltage drop to premises at the far end, we will inevitably be at the high end. Indeed, my barn / workshop is a direct cable from the transformer pole, and the farm house is 'one pole further downline', and typically there is a one volt difference in the mains between the two.

In the picture, the cable going to the left feeds only my barn / workshop, and the cable going right feeds the house then onwards to our neighbours half a mile away, and a small industrial estate.

[awemawson]

Now we've had problems with rather a lot of bulbs blowing, especially LED GU10's , but when I've measured the mains it's always been within the legal specification of 253 max.

However, when I fitted UPS's to the PC's, they continually monitor the voltage, and were giving me high voltage alarms. Plotting out the recorded data it was obvious that when the load was low 'down line' at night, in fact the volts were going as high as 256 and once 257.

I reported high voltage, and a 'UK Power Networks' man came out, measured, said it was in spec but on the high side, and although he couldn't act on my figures agreed to fit a voltage recorder for a week to see using their own calibrated instruments.

Sure enough his measurements exactly traced mine, so he went out to the transformer and inspected the 'tapping switch', which was set to the highest voltage. That's wrong he says, they should always be 'one tap down' or even more - I'll get it altered.

That was in early July. Since then we had a further five visits by various bits of the organisation 'just checking' resulting eventually in a notice through the door advising of a 'scheduled power cut' for today (8th December). Hooray - at last - about time.

So 09:30 this morning a large Unimog access platform, and two vans arrived. First thing to do was set out a matrix of earth stakes and earth the Unimog, that had churned it's way into our goose field.

Then they pulled the LV (415v) 200 amp fuses on the transformer pole. Then they had to 'mark the pole' to stop anyone else re-fusing

[appletree]

You can get a box of tricks which attenuate the supply voltage and thus reduce the current drawn, might be worth it on the 240 house supply, I can imagine your volts are all over the place, also if there are Solar panels on that feed they can impact.
When I was an Instrument apprentice my mate was in the electrical section his boss went to great lengths with power factor correction

[pete3000]

Technically should be 230v/400v the old standard was 240v/415v. Sounds like someone has done their tapping wrong...... as you have found out. Didn't you measure the 11kv to see if it was in spec lol

[awemawson]

Next they chopped out a section of the feed cables from each phase of the 11kV overhead line down to the transformer - all done live using long fibreglass tools and rubber gloves.

Two man job, with one cutting the cable and the second grabbing the cut off bit to stop it falling onto the transformer

[awemawson]

Then came the 'tap changing' - this transformer seems to date from the 1950's. The 'tap switch' was locked shut, but the lock got cut off with a big cutter. Then the chap trying to alter it convinced himself that it didn't 'feel right' - certainly there were no 'clunks' as it rotated - indeed it rotated apparently quite freely.

We had visions of something from the switch mechanism falling off inside the transformer, so having theoretically moved it two tap positions they decided to temporarily re-connect to measure the voltage (which had been 250 / 251 when they arrived)

Hooray - 240 volts phase to neutral - the switch must be ok 

[awemawson]

So then they could take off the temporary connections and re-crimp onto the stubs left where they cut the three phases.

To do this the various live cables were wrapped up in blanket red rubber  insulation, just in case something fell or went wrong

Then they moved their 'vehicle collection', back out into the yard to try and start trampling down the horrid mess they made - very soft clay soil that goose field 

[awemawson]

In fairness we've been offered a load of top soil and grass seed and a gang to spread it so they are trying to make things better !

And the result. Well now there's a bit of load back on the line my UPS here in the barn where I am typing is reporting 235v - I've never known it as low as that all the time we've been here. Just as well, as  while this was going one I took delivery of another batch of GU10 LED bulbs from Wickes (special offer half price at the moment  )

[lordedmond]

That brings back some memories from my past enjoyed live live working up the poles but not so much underground cable work , that's the price you pay for being a SAP amongst other things


The job I disliked the most was phasing out 11KV with two probs ( high res stacks ) inside the truck enclosure no room to move

All the tap changers I have delt with have been clunky and stiff as Blazers no wonder they had doubts

Glad they dropped you a wee bit now the boss lady will tell you the electric oven is not up to snuff 

Stuart

[John Rudd]

As an ex instrument type, dealing with anything greater than 24v dc gives me the willies......

Rather them up the pole than me at 11kv.......

[AdeV]

Watching men work on live 132kV cables (the ones on big pylons) is pretty scary... they drop them onto the cable with helicopters! 

[awemawson]

If, on a dry day a pigeon lands on a 132kV line, then flys off and lands on the ground, does it get a shock at either end of it's journey 

[lordedmond]

no

just a tingle in its feet 


i should not tell you this but levy can transform a crock of a bull to a pedigree bull , it works like this

a earth fault up a wooden pole over head line , thus a voltage gradient in the ground bull walk to pole and gets 20 volts between front and back legs DEAD bull on insurance claim its the pedigree bull QED

hence a sparks will take very small steps when approaching wooden poles you do not want  volts across your legs 

Stuart

[vintageandclassicrepairs]

Hi Andrew and All,
WHen I first looked at your photos I was puzzled as to why they cut the droppers to the transformer ?
Then I noticed that theres a HV cable heading off underground, Is this the supply to the ind estate?
Usual method of isolating the trafo would be to pull the HV disconnect on the pole just before the trafo
Obviously they did not want to disrupt supply to the cable ??

I worked regularly in the outdoor 110Kv switching and transformer compound attached to the Power station where I was a spark and later also undertook instrumentation
I found that workking near HV would lead to chronic fatigue ?? it was also very difficult as the ground was covered in a layer 2-4 in. stone
One job I undertook there involved recabling from a generator breaker to the 10/110kv tranformer
The old cables were  paper insulated, lead sheathed, steel tape armoured ! 3 x 300 sq mm.
8 runs of cable about 100yds long in a concrete duct
These had to be cut in 3ft lenghts and manually carried out due to live overheads 
The new cables were 24 runs of single core 300sq XLP copper, so they were cleated together every metre or so in threes, giving  8 runs of 3 phase "cable" arrangement ,
The end terminations had " 3M cold shrink" silicone rubber insulators

All this was replaced with an indoor SF6  gas insulated indoor setup about the time I took Voluntary severance 6 years ago
Best move I ever made 

John

[awemawson]

The transformer is fed 11kV from two directions. There is the overhead route via that isolator that you have spotted on our boundary with the water pumping station, then there is the red cable running down the pole which crosses our drive underground, and goes across the A21 to another pole where it continues above ground.

The industrial estate is only fed 415 v three phase in the bundled cables to the right of the transformer that call first at our house where we take one phase at 240.

Incidentally the water pumping station has a three phase 415 v feed down the pole and into their premises under our vegetable patch for which I don't think they have a way leave, a fact I'll keep up my sleeve I case I need leverage in the future 

It seems that somehow they weren't told about the arranged power outage, so they've had yellow flashing lights there this evening sorting out whatever mayhem it caused their system!

[awemawson]

So I thought it'd be interesting to see the over night results from the UPS voltage recordings:

First picture as it was one night in July - significant over volts in the small hours

Second picture - last night - far more healthy

[vintageandclassicrepairs]

Hi Andrew,
Good to hear you have a resolution to the issue,
My house  is supplied from a tranformer which used to be pole mounted near the road boundary in my garden
We had problems back then with short bulb life as we were nearest the trafo and it suppleid houses up to half a mile away,
When the networks were upgraded and a 3 phase transformer installed I got them to move it into the field outside my garden, so things look a little better
The supply is now more stable.

I'm still puzzled by the way your transformer is supplied?
Here in Ireland every rural transformer is fed through fused links and usually there are arc suppression coils as well
The fused links have a fusible element that is attached in tension holding the latch on the disconnect link
if the fuse blows the link drops open, This visual is very useful when fault finding at night
Remembering this, it seems a long time ago now, I left networks in 85 and moved to the power station

Cheers
John

[lordedmond]

John

It's not unusual with older instalations , I bet it was the only transformer on the line and they tagged on the extension Hv line , with the LV side they are Evan more caviller they usually have very little protection .

In fact older style switch gear for Hv they had a six second handle so you could not open the breaker for six seconds ,by that time if there was a fault it would trip upstream , for those that do not know it was a hinged leaver that you took off and turned round to open the switch to OFf

glad I do not play with it nowadays

Stuart

[awemawson]

i suspect Stuart is right here. I have seen photograph from the mid 1930's showing an HV 3 phase line in that position, but without the underground cable down the pole. It must have been replaced at some time in the 50's with the current one, as when we dug out for the slab for the green houses we unearthed the stumps of the original poles and the 1/4" thick solid copper earth plane 

[johnbaz]

Since I saw a poor fella cooked to overdone on top of a train in India (On youtube), The very thought of all the volts and megga amps chill me to the bone for anyone working on the lines 

I'm happy to have it all normal here in the city!!


John 

[kayzed1]

Glad you are sorted, today we had a whole 80volts in our mains, the myford ran at 43rpm then stopped but my L E D machine lamp still worked until i turned it off.

[lordedmond]

Since I saw a poor fella cooked to overdone on top of a train in India (On youtube), The very thought of all the volts and megga amps chill me to the bone for anyone working on the lines 

I'm happy to have it all normal here in the city!!


John 

John

All you need to remember is

It's the volts that jolt
But it's the mills that kills

(Mills - milliamperes )

Sorry sparky humour
Stuart

[kayzed1]

In prep for the arrival of my 3phase kit for the Mill i have today gone around the shed and linked all the metal with a 20mm earth cable. this i also fixed to the shed earth plus a link to out side and a 5foot earth spike knocked into the field next door i have a good earth in the house also from when we rewired the place 5 years ago, down to my last 10mt of cable now.

[lordedmond]

Now get a AC volt meter test the phase to neutral and take a note of it

Now disconnect the earth conductor that goes to the earth rod at the point were it connects to your system , now test from phase to the conductor that your disconnected , it should be as near as damit is to swearing

Do not forget to reconnect the conductor after the test


Now this is not the correct method as it involves putting in temp earth pegs a certain depth and distance , but it's a good indication that you do have a earth not just a rod in the ground


Have fun and be safe

Stuart

[kayzed1]

my 3 phase kit arrived today i had been to hospital so it was good to have some thing to play with to take the mind of whats to come......
 unboxed it and carried it all around to the shed, spent an hour removing the wiring from he mill and rewiring to run the 110v
 power feed  and 24v lamp, removed the switches and other guff and tested the power feed and lamp. Removed the old motor
and checked all looked OK with the new one and fitted power cable and humped it onto the plate. i had to make a shim/spacer
for the pulley to get it to sit correctly. Made up a new 240v lead with new plug and fitted the VFD to the mounting plate i made,
Simple job to wire it up and it runs nice with a lot less din that of the old single phase motor. i am half way through making a
a plate to mount the remote on the belt cover, pics if i can when fin.
Lyn.