Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[tickmike]

I just thought this may be useful .
While I was on one of my countryside walks yesterday spotted some trees growing very close to some high voltage overhead power lines (11Kv), it was next to a public footpath that went through a picnic area where young children could play on / push the branches on to the overhead power line  .
On the wooden support poles you should find a plate with a free phone number and also a  pole or support number, make a note of them and then  phone the number and give the details about location and support number and the problem.
I could not get to the support pole because of the thick undergrowth so I used one of the numbers below and give them my phone number, the ordnance map ref number, then someone phoned me back within a few minutes.

Western Power Distribution
Emergency telephone numbers

Midlands East    -    0800 056 8090
Midlands West    -    0800 328 1111
South Wales    -    0800 052 0400
South West    -      0800  365  900

Or look up your local power Distributor.

[burakkucat]

Good advice, Mike.

I'm sure Walter will have many a tale to tell of dangerous situations, with either HV or LV plant, that he has discovered when out and about in the Surrey countryside.

[oddlegs]

I just thought this may be useful .
While I was on one of my countryside walks yesterday spotted some trees growing very close to some high voltage overhead power lines (11Kv), it was next to a public footpath that went through a picnic area where young children could play on / push the branches on to the overhead power line  .
On the wooden support poles you should find a plate with a free phone number and also a  pole or support number, make a note of them and then  phone the number and give the details about location and support number and the problem.
I could not get to the support pole because of the thick undergrowth so I used one of the numbers below and give them my phone number, the ordnance map ref number, then someone phoned me back within a few minutes.

Western Power Distribution
Emergency telephone numbers

Midlands East    -    0800 056 8090
Midlands West    -    0800 328 1111
South Wales    -    0800 052 0400
South West    -      0800  365  900

Or look up your local power Distributor.

On a related subject.
If you ever come across a downed high voltage power line give it a very wide berth.
The distribution companies nowadays make extensive use of devices called "auto reclosers".
These are in-line circuit breakers that are designed to re-energise a tripped overhead line several times before eventually "locking out".
Many line faults are of a temporary nature such as a bird bridging lines with it's wings or a tree branch being blown by wind onto a line. The use of auto-reclosers mean there may be no need for an engineer to replace fuses.
I know of someone who tried to help at a night-time road traffic incident and didn't realise that a cable had been brought down when the car hit a pole. The line re-energised and he was very lucky not to be killed although he did lose an arm and a leg.

[Black Sheep]

Oooooooh !! Poor fella. 

Great advice Oddlegs.

[tickmike]

On a related subject.
If you ever come across a downed high voltage power line give it a very wide berth.
The distribution companies nowadays make extensive use of devices called "auto reclosers".

Yes that's good advice.
I remember when I was on a visit to a power station and was near a  large circuit breaker and you have guest it operated under fault conditions, the noise was incredible and the speed it opened and closed and then locked out was just amazing (we were later told a JCB digger had gone through a main cable.) 

Hi and welcome oddlegs.

[oddlegs]

On a related subject.
If you ever come across a downed high voltage power line give it a very wide berth.
The distribution companies nowadays make extensive use of devices called "auto reclosers".

Yes that's good advice.
I remember when I was on a visit to a power station and was near a  large circuit breaker and you have guest it operated under fault conditions, the noise was incredible and the speed it opened and closed and then locked out was just amazing (we were later told a JCB digger had gone through a main cable.) 

Hi and welcome oddlegs.

A few years ago I visited Eggborough Power Station on business. I was told to park my car in a marked bay directly under some very low high voltage cables that ran from one of the Generator Unit-Transformers to the National Grid Switching Station at the other side of the road.
I tentatively stepped out of the car and as I stood up I felt my hair standing on end. The hissing from corona losses was frightening and of course the transformer (500 MVA) was making a right racket.
To stand in the control room and look at the big digital displays in each of the four corners, each of them reading 499/500 MVA was quite something. At that time Eggborough was a base load station and running flat out 24/7.
I think the very quick re-closing times on big breakers is not typical for rural light lines. I understand that settings of up to several minutes are possible.

[Black Sheep]

We OR engineers have to be specificly trained to work in, or within, 100mtrs of generating stations. We call them 'Hot Sites' and anything beyond the 100mtrs is classed as a 'Hot Zone'.

I am one of these engineers and believe me, when working in one of the buildings within the GB's compound, the buzzing, hissing scares the hell out of me !!

We have to fit special fibre-link isolators, and other electronic isolator cards if installing any of our equipment within an area marked as a Hot Site. If the circuit is a DSL one, then there are two Isolating Units used. The price ?? approx £500 I was last told. 

[c6em]

Ah, this is/was my "field"
Anything less than 11Kv at 50Hz and 13.8Kv/60Hz (being the standard generating voltages in UK/USA) and a few thousand amps then my employers wen't interested.

Big transformers have blow out panels so if there is a mega overload the specially weakened calibrated panel bursts and the hot burning oil "vents".
Otherwise a major fault inside would turn the whole thing into a pressurised bomb.

Don't know much about high current switchgear design but as I recall the large units need some sort of compressed inert gas blasted in at high pressure to blow out the arc as it starts to be formed as the contacts are powered away from each other.  I'd guess they are not quiet in operation!

[oddlegs]

Ah, this is/was my "field"
Anything less than 11Kv at 50Hz and 13.8Kv/60Hz (being the standard generating voltages in UK/USA) and a few thousand amps then my employers wen't interested.

Big transformers have blow out panels so if there is a mega overload the specially weakened calibrated panel bursts and the hot burning oil "vents".
Otherwise a major fault inside would turn the whole thing into a pressurised bomb.

Don't know much about high current switchgear design but as I recall the large units need some sort of compressed inert gas blasted in at high pressure to blow out the arc as it starts to be formed as the contacts are powered away from each other.  I'd guess they are not quiet in operation!

One of my first jobs as a young apprentice electrician was to take an oil sample from a large recently installed distribution transformer.
I removed the blanking plug from the valve down at the base and held my glass beaker to it as I carefully opened the valve.
A terrific blast of high pressure oil knocked the beaker to the other end of the sub-station.
The transformer was fitted with an oil conservator tank above, with the usual Buchholz relay, to detect internal transformer faults in the pipework between transformer and conservator tank. The air breather and explosion relief vent were both fitted to the conservator.
Investigations proved that when the transformer was installed, some Herbert forgot to remove a solid steel blanking disc in the pipework to the conservator.
When the transformer warmed up there was no where for the expanded oil pressure to escape.
Because the transformer was a large one there was enough give in the steel tank sides to acommodate the pressure build up.
In those days the only explosion relief was a thick mica disc about 4 inches diameter on top of the conservator.
The inert insulating gas used in switchgear and bus-bar chambers is sulpher (sulfer) hexafluoride (SF6). It is used for voltages ranging from 400kV to 11kV.  Air blast circuit breakers use huge quantities of high-pressure compressed air released suddenly by giant poppet valves and make a terrific row. I worked at a steelworks where the arc furnace transformers were switched by ABCB's and the racket could be heard from miles away.

[Black Sheep]

That's a great insight lads. 

[tickmike]

About 30 years ago I drove past a small sub-station and it blow up with a loud bang and lots of sparks / flames and everywhere went black 

[Black Sheep]

Did you happen to see Oddlegs and c6em running in the opposite direction tickmike ?? 

[AdrianH]

Back in my early teens my brother and I were walking home one night when the substation in our road went up.    I will never forget the noise and the hot air from that thing going off, we were only @ 30 yards from it .
I am always surprised that these things can be sited next to footpaths and not have more protection, there must be the potential for flying debris. In those days it was just a 3ft. wooden fence and some bushes around that. Anyone could have climbed in there.

[oddlegs]

Back in my early teens my brother and I were walking home one night when the substation in our road went up.    I will never forget the noise and the hot air from that thing going off, we were only @ 30 yards from it .
I am always surprised that these things can be sited next to footpaths and not have more protection, there must be the potential for flying debris. In those days it was just a 3ft. wooden fence and some bushes around that. Anyone could have climbed in there.

The 11kv switchgear I used to work on was rated to deal with a fault energy rating of  250MVA.
That is the equivalent of 250,000 1 bar electric fires or a mechanical power of approx 250,000 horse power.
There is a good reason why sub-station door are arranged to open outwards.      
Older substations were fitted with oil filled switchgear which would add to any explosion, nowadays modern substation switchgear is likely to use vacuum switches with air insulation, or inert SF6 (sulpher hexafluoride) filled switchgear.
The transformers are still normally oil filled but epoxy insulated transformers are available (although very expensive) where the transformer is within a critical location. During the sixties there was a move towards silicone oil or even worse PCB filled transformers but these were found to cause terrible environmental damage.
I once saw the concrete cast roof of a large industrial substation blown into a low-earth orbit by a transformer fault.
I wasn't responsible for that one, it was at a neighbouring factory.   
I wouldn't hang around in front of a sub-station, high energy power is not something to be trifled with   

[tickmike]

I wouldn't hang around in front of a sub-station, high energy power is not something to be trifled with   

Another place you got to be careful where you sit in Electric trains, This relates to EMU's (Electric multiple units ) Not the Electric Loco hauled trains .
On EMU's you do Not want to sit in the coach with a Pantograph (device to pick up the power from the overhead line ) on the roof.
There is a 25KV cable that comes from the pantograph THROUGH the inside of the coach ( back of some wooden panel  ) to the transformer underneath .
When I was in research on the railways we had a few off these cable to find out why they had blow up  not a pretty sight inside of the coach.

Edit . I also had some transformers to take to pieces to see why they had exploded !