Pikeys and a stolen substation neutral cable = BANG!!!

[Kirchoff]

Hi,
I heard about this on the news. Apparently all the local residents' appliances blew up due to a voltage spike.

I couldn't figure out at first how this happened? Then I started wondering whether, because the secondary winding of the transformer is a 'star' winding and the centre the 'earth/neutral tap it must have caused an inbalance in one of the legs leading to the voltage surge?

I'm not sure if I'm right as I've not worked for many years (ill health).

Any other ideas?

 

[Engineer54]

Quite frankly, i don't believe a word of what's been reported here. The protective relays would have tripped the system out long before any damage could have occurred!! Unless they had been defeated, by trained technicians. Highly unlikely!!!

Many such instances are generally reported by those that haven't got a clue of what their writing about!! lol!!!

 

[Kirchoff]

You may be right, but they interviewed the residents and filmed their broken appliances. But I do agree in that the media put a spin on everything (if not make up) their stories to create shock value, ala Daily Mail.

 

[Silly Sausage]

Unless they had been defeated, by trained technicians. Highly unlikely!!!

Haha!...BEng(Hons) pikeys!

 

[Knobhead]

I’m not one that normally disagrees with you EN54 but look at the normal protection for a “ring” tee switch. HV O/L only! No REF or secondary O/L other than the local fuse pillar.

Knowing where to make the first cut is important to keep you alive, but it’s not rocket science!

Myself and a few of my mates could make some money out of this

 

[mechelec]

if you remove the star neutral to earth link (low voltage as it is a delta star transformer)at a substation you will then have in effect a floating earth as the centre point of the transformer has no reference to earth. If the three LV phases are balanced then all will be well, but on a distribution sub with multiple domestic customers it is a very very unlikely situation. As would normally be the case the load would be imbalaced and therefore you could have anything from 0V - 400V(declared voltages) seen on either of the three phases. This situation will result in up to 400V seen on appliances with no neutral return path. As we know electricity will always follow the path of least resistance and any electronics circuits with filter circuits will be fried.
Eng 54 you may have different protection on the subs where you are but I can assure you the distribution subs around me have BS88 fuses as protection of the LV feeders (and a few ACB's to individual customers) and these will not clear a fault as described above. The ame situation arrose locally some time ago and meant the removal of all cutout fuses to 250 properties (including breaking in to empty properties with police escort) one poor woman arrived home 30 minutes after they had broken into hers poor thing

 

[Engineer54]

I’m not one that normally disagrees with you EN54 but look at the normal protection for a “ring” tee switch. HV O/L only! No REF or secondary O/L other than the local fuse pillar.

Knowing where to make the first cut is important to keep you alive, but it’s not rocket science!

Myself and a few of my mates could make some money out of this

Ah, if your just talking about an isolated local distribution TX controlled purely by a RMU, Yeah!! But maybe i was thinking along more grandeur lines when talking about a ''sub-station''!! ...lol!!! How much of a length of neutral cable would they achieve in one of those sub-stations?? hardly worth getting out of bed i would think, especially when your putting your life at risk in the process!! ...:nuke:lol!!! :uhoh2:

 

[Engineer54]

Thinking further on the subject, it would also depend on what sort of LV protection they had on the main switchboard in this distribution sub-station. I know many used to have EFF on the main TX LV supply cables, not so sure on the much smaller set-ups though!!!

 

[mechelec]

its all small subs around here. The largest 11KV-400V subs are only 1000KVA

 

[Engineer54]

if you remove the star neutral to earth link (low voltage as it is a delta star transformer)at a substation you will then have in effect a floating earth as the centre point of the transformer has no reference to earth. If the three LV phases are balanced then all will be well, but on a distribution sub with multiple domestic customers it is a very very unlikely situation. As would normally be the case the load would be imbalaced and therefore you could have anything from 0V - 400V(declared voltages) seen on either of the three phases. This situation will result in up to 400V seen on appliances with no neutral return path. As we know electricity will always follow the path of least resistance and any electronics circuits with filter circuits will be fried.
Eng 54 you may have different protection on the subs where you are but I can assure you the distribution subs around me have BS88 fuses as protection of the LV feeders (and a few ACB's to individual customers) and these will not clear a fault as described above. The ame situation arrose locally some time ago and meant the removal of all cutout fuses to 250 properties (including breaking in to empty properties with police escort) one poor woman arrived home 30 minutes after they had broken into hers poor thing

I bow to your experience in this matter mechelec. Yes i'm afraid your right , i am use to a far more sophisticated set up than 3 BS 88 fuses in the package sub-stations we install, on both the MV and the LV side..lol!!! But, i have been in a few of the bigger localised sub-stations in the Essex area, and have seen protective relays in use, on both the HV and LV side.

 

[alanl]

It can happen (blowing appliances). I did a course last year, and on it was an EON employee whose sole job was to repair damage that they, and the copper thiefs have caused.
It wasnt common, but does happen infrequently when a length of copper is taken from a substation that a quick jolt of high voltage goes down the existing 230v lines.
Anything plugged into the mains at the time is usually fried.
We then had a talk about surge protection devices, and they would not help, as the belt of HV usually went down the neutral or earth. Apparently the incoming 100A fuse does not blow either. He says a few houses have caught fire because of this.
Alan.

 

[Justin pearson]

i use to work for transco in the office organising repairs and replacements of the big transformers in powerstations around the country.

I lost count as to how many power stations where broken into and the earth rods where cut and stolen (Very large Earth Rods). I am sure that any SAP's in the forum will tell you how dangerous it is walking through a live power station with anything metal in your hands.

I never saw any fried copper thieves though.

 

[jay sean]

Our company sent us to do the CP course, we went to Drakelow grid, just the humming of the tx and the overhead cables gives you the willies, don't know how the pikeys have the guts to do that.

 

[Knobhead]

Many years ago I went to the EMEB training collage, at that time remote 132KV protection was by fault throwers. Basically a high speed switch would cause a dead short to earth on the centre phase, the primary station would then register a fault and open the OCB to that feeder. OK until the Pikeys have nicked the earth return from the fault thrower, it’s f-all use then. One or two got their just deserts, DOA when the engineers got there!

 

[Justin pearson]

and on a foggy wet evening they crackle, and spit i wouldnt want to walk round them with a step ladder on my sholder. I forget exactly what they told us on our training, in nottingham where they have fake power station training centre is, as it was so long ago now but getting within 1.2m of some of the bits will arc across and give one hell of a packet.

 

[JD Hogg]

Yeh I live quite near a grid substation, does anyone know why the transformers hum?

 

[Justin pearson]

they dont know the words

 

[JD Hogg]

Lol ...

 

[Justin pearson]

no i dont,but i know they are expensive very b***dy expensive and we were planning for work that was going to happen ten years later.

Im not sure if that was because the maintenance teams were very slow, or it just took that much planning. But i suppose if you are switching of a power station in a big city i can imagine it takes some planning.

Think of all the tea and sandwiches they would have to make for the workers.

 

[Engineer54]

Yeh I live quite near a grid substation, does anyone know why the transformers hum?

IN very simple general terms, ionisation of humid air is the hissing noise and the the humming is the the iron core lamination's vibrating under load... All in most circumstances very normal!! However, differences in these humming noises can to a trained ear indicate underlying problems with a TX. Also different TX constructions, different humming noises....

 

[Knobhead]

One to add to the experience pile. I got a call to a plant, all the office equipment had failed. On arrival I tested the supply to the office and all seemed OK. Called the lads from office services to come and sort their junk out. (It was junk, it's a wonder you didn't need to shovel coal in to the computers). All power supplies smoked! I'm puzzled now, how could 4 go wrong together. Got talking to the plant manager and he tells me that the lighting had "gone weird" for a while. Went back and checked the Ph -N voltages again and all OK.
It wasn't until lunchtime when I got talking to some of the other electricians that things became clear. Two of them had installed a 150mm 3½C cable in to the plant main switch board that morning and had disconnected the neutral - earth cables to make it easier to get their cable in, when finished they reconnected them. To quote one of them "I thought there was a bit of a spark!" What galled me was I'd fitted an engraved warning label to the earth bar when I installed it!

 

[Knobhead]

and on a foggy wet evening they crackle, and spit i wouldnt want to walk round them with a step ladder on my sholder. I forget exactly what they told us on our training, in nottingham where they have fake power station training centre is, as it was so long ago now but getting within 1.2m of some of the bits will arc across and give one hell of a packet.

Which one did you go to? The first one I went to was Ashover Hall but this was closed down and a new one opened at Radcliff power station. Ashover Hall was a beautiful place, when you went out to do the practical switching part of the course it was like going on a nature ramble. When I want to Radcliff the HSE had ruined the course it was so watered down. The “students” were no longer allowed to touch the U/G link boxes, I had a great time at Ashover paralleling transformers with solid copper links, lots of pretty blue sparks.

 

[mechelec]

I have spent a lot of time at ratcliffe on various courses, they have a pretty good 11KV network which they power up so that you can sectionalise, isolate and test on etc. If I remember correctly it is run at less than 11KV with very fine protection.
Im not sure what will happen to the training centre as western power have taken over from eon. The last time i was there there were rumours of some staff being finished. They had recieved a price to move the training network and werent sure if they would move it or leave it at ratcliffe. I would imagine the training centre would struggle to keep going if WPD stopped sending their guys there.
Ashover hall had finished when i started but I have heard stories of how good it was. my mate used to take his bike and go cylcling in the evenngs when he was sent. Did you stop in the digs Tony?

Engineer54 I wish there was some sort of monitoring on the LV side. The times I go to customers off supply and they say "you took your time I waited and waited for someone to come out". I ask how long was you off supply before you rang. usually it went off hours before and they think we know. We totally rely on customers calling us. If your power is off and you dont call no one will ever know, be it one house or an industrial estate (LV). Another point is if we have an OC LV mains fault it can make it easier to find if all affected customers call in.
On the HV if a pigeon farts on the line control know. it has been more geese flying into the line this week funnily enough i have had 3, 2 were on saturday. bloody tasty too on sunday.

 

[Justin pearson]

Ashover Hall it was indeed a nice place

 

[Knobhead]

Digs! The place was like a 5 star hotel. We’d go off to the local pub in the evening, on arriving back at the hall a buffet would have been laid out by the housekeeper. 4 meals a day!

As to the 11KV it was what the label says. The system was feed by four .433/11KV high reactance transformers, it could kill you quite well. You know the voltage was right as when you isolate an OCB you get a hiss as the contacts part. I was very twitchy doing live phasing out for the first time at Ashover, and to be honest over the years I was no less twitchy doing it.

Below is the set up at Radcliffe.

View attachment 7211

 

[aptsys]

As we know electricity will always follow the path of least resistance and any electronics circuits with filter circuits will be fried.

Electricity will follow ALL paths of resistance.

 

[mechelec]

Electricity will follow ALL paths of resistance.

I was just trying to explain basically if the neutral is lost as a return path in a piece of connected equipment then electricity will follow the path of least resistance in the equipment back to source to make a circuit!!!!!!

 

[aptsys]

I was just trying to explain basically if the neutral is lost as a return path in a piece of connected equipment then electricity will follow the path of least resistance in the equipment back to source to make a circuit!!!!!!

...AND all the other return paths. Not just the path of least resistance.

 

[Knobhead]

If you want to know what’s happening to the phase-neutral voltages you have draw out a vector diagram of the currents and then transpose voltages on top of it.

Basically to comes down to:
The phase with the lowest load will have the highest Ph-N voltage. That’s the phase that first blows things up. That drops the loading on that phase even more causing more imbalance and an even higher voltage rise.

End result, one estate with irate customers wanting compensation and a couple of house fires!

I will try to do a vector for you, but it’s not easy so give me time.

 

[Dunc]

I love these posts about the MV/HV side of things. Most of my work is domestic with the odd commercial/light industrial job so most of this stuff goes right over my head but interesting reading none the less.