Small 11Kv cable fire London...

[PEG]

...And the other issue,is the tunnel/ducting systems will invariably contain "other" services,including OSA facilities,which they could tell you about,but would then have to terminate you...:biggrinjester:

Years ago,i was involved in work,in city centre Manchester,and we all had to sign OSA papers,but there is no secret concerning the craftsmanship in those sewers and ducts,and the myriad of links between services,down there.

I recall one tunnel,where there were 80+ cables,pipes and ducts,a mixture of power,telecommunications,gas and who knows what else...a fire in one similar,would tilt a jointer towards,depression :icon12:

 

[Knobhead]

As far as i'm aware, all of the local MV/LV distribution network TX's are Dyn 11 (delta/wye). N-E Resistors would only be used where it is requirement to limit the fault current on the LV side. Earthing electrodes for MV and LV systems are generally separated at TX locations unless the Ra value of the electrode systems are of a suitably low value (under 1 ohm).


I don't consider MV/MV TX's as being particularly part of a local network distribution system, although in Central and the City of London the networks have been reinforced and evolved many times often in not exactly the best way, so it wouldn't surprise me at all that N-E resistors have been used quite extensively.

Local distribution transformers 11/.433KV Dy11, up to 1000KVA 4.5% imp, 1500KVA 5% imp.
Star point neutral solid earthed. (TN-C)

Primary transformers 33/11KV Dy11+OLTC
Star point impedance earthed. (IT)



A little gem I found last night while reading up on something else.

London’s predominant network assets comprise approximately:

2,000km EHV cables (above 11kV)
8,000km MV cables
19,000km LV cables
100 EHV/MV substations
13,000 distribution substations
2.1m customer connections

Hardly surprising there’s the odd failure.

 

[Engineer54]

Local distribution transformers 11/.433KV Dy11, up to 1000KVA 4.5% imp, 1500KVA 5% imp.
Star point neutral solid earthed. (TN-C)

Primary transformers 33/11KV Dy11+OLTC
Star point impedance earthed. (IT)



A little gem I found last night while reading up on something else.

London’s predominant network assets comprise approximately:

2,000km EHV cables (above 11kV)
8,000km MV cables
19,000km LV cables
100 EHV/MV substations
13,000 distribution substations
2.1m customer connections

Hardly surprising there’s the odd failure.

That makes sense!!

What KV values are you/they calling EHV?? I wouldn't call either 33/66KV EHV, one is the top end of MV and the other would be HV.

I've been told that central Londons (west end) network and to a lesser extent the City of London network is in dire need of a complete redesign having been reinforced many times as cheap stop gaps to keep supplies running. The cost in time materials to undertake this work, scaring the life out of the private DNO's!! lol!!

The only time i've ever used impedance earth resistors is on MV generator installations...

 

[Knobhead]

The document I was reading was concerned with 11KV rings only so anything above was out of its scope.

I found it very interesting, they’re using automatic sequenced switching to move the OP under fault conditions.


All the 33/11KV 20MVA and 11/3.3KV 4MVA transformers were impedance earthed star point.
Smaller 11/3.3KV transformers were solidly earthed star point. The E/F relays being fairly sensitive as they only fed one load.

 

[Engineer54]

Are they still using 3.3 KV TX's on London's networks??

I like a good read sometimes that's interesting and holds my attention, got to be better than reading about someone's RCD tripping out intermittently, or what's the best way to wire a shed/garage!! lol!

 

[Knobhead]

I was referring to the transformers I’ve worked on.

They still use 6.6 in London and parts of the NW. That wasn’t what I was reading about last night.

It was system reliability I was interested in. I set off looking for E/F passage indicators. That led on to automatic switching for RMU’s.

 

[UKMeterman]

To increase "reliablity of supply" in the "City" the LV supplies are fed from two MV transformers and have a reverse power relays and ACB at each sub station. This means that the LV fault level is very high, I wonder if this has added to the intenensity of the pavement explosions and so on.

 

[Engineer54]

To increase "reliablity of supply" in the "City" the LV supplies are fed from two MV transformers and have a reverse power relays and ACB at each sub station. This means that the LV fault level is very high, I wonder if this has added to the intenensity of the pavement explosions and so on.

From my understanding, the fault levels are very high throughout Central London and the City of London.
The fire as far as i can see is located in the West End (Central London) not in the City...

 

[UKMeterman]

Have a google for
[h=2]Search Results[/h][h=3][PDF]Long Term Development Statement - UK Power Networks[/h]

 

[Engineer54]

Have a google for
Search Results

[PDF]Long Term Development Statement - UK Power Networks

An interesting read, though quite a bit of waffle is going on in that report. I wonder what they actually mean by ''Long Term Development'' because the areas i've already pointed out have been in dire need of development since i was a lad. As i said the costs involved, especially in Central London are going to be astronomical and must be scaring the crap out of these private companies, that will probably move on before any real work is undertaken....

 

[Knobhead]

To increase "reliablity of supply" in the "City" the LV supplies are fed from two MV transformers and have a reverse power relays and ACB at each sub station. This means that the LV fault level is very high, I wonder if this has added to the intenensity of the pavement explosions and so on.

I was reading about it last night after I found the fault passage indicator info I needed. I got reading about the MV protection and automatic switching.

It’s highly unlikely they’ll run transformers in parallel, purely down to the fault currents local to the substation. You have to take in to account the low system impedance on the MV side feeding in to the transformer.

There was another well publicised incident recently where a LV UG link box failed. It could have been O/L or water ingress which some are prone to. I know one thing, I don’t like them.

From my understanding, the fault levels are very high throughout Central London and the City of London.
The fire as far as i can see is located in the West End (Central London) not in the City...

The line to line fault currents will be high, at least using NER’s the line to earth current can be limited.

 

[Engineer54]

I was reading about it last night after I found the fault passage indicator info I needed. I got reading about the MV protection and automatic switching.

It’s highly unlikely they’ll run transformers in parallel, purely down to the fault currents local to the substation. You have to take in to account the low system impedance on the MV side feeding in to the transformer.

There was another well publicised incident recently where a LV UG link box failed. It could have been O/L or water ingress which some are prone to. I know one thing, I don’t like them.




The line to line fault currents will be high, at least using NER’s the line to earth current can be limited.

As i say, i think the patch and fix thats been going on for years will continue, with no real effort in sorting out the distribution system as a whole. In Central London the main problem is space and being able to maintain supplies while they are installing the new upgraded system. ...And of course the costs involved, that will just keep getting bigger the longer they leave it and keep installing patching work...

 

[UKMeterman]

Hi,
I have seen some new 132KV subs being installed on the outskirts of the city (Finsbury) and there have been other changes.
As to Tony's point please read the document I linked to, the two transformers in parrell is exactly what they are doing...!

 

[Engineer54]

Hi,
I have seen some new 132KV subs being installed on the outskirts of the city (Finsbury) and there have been other changes.
As to Tony's point please read the document I linked to, the two transformers in parrell is exactly what they are doing...!

Not exactly a good practice though is it? Looking at those single line drawings in the link, isn't instilling any confidence on my part in the security of network systems they are currently supplying...

It's the Central London distribution networks that need a total overhaul, where there is just no space to accommodate upgrading. Finsbury, or other outskirt areas is another world compared to congested areas of London...

 

[Knobhead]

Hi,
I have seen some new 132KV subs being installed on the outskirts of the city (Finsbury) and there have been other changes.
As to Tony's point please read the document I linked to, the two transformers in parrell is exactly what they are doing...!

Learn to read drawings.
The transformers that look like they are in parallel are feeding the 11KV network. They are dual star secondary. They aren’t separate units in parallel.

I was referring to LV being in parallel. The MaxPFC would exceed the LV pillars rating.
Some LV pillars incorporate automatic change over of transformers, the MG SAIF springs to mind.