Small 11Kv cable fire London...

[UKMeterman]

There seems to be a small cable fire in London, has affected key parts of the MV network BBC Local Live: Updates from London on Wednesday 1 April 2015 - BBC News

 

[Fin170]

If only the housing of the joint was metal....

 

[Darkwood]

If only the gas line wasn't run so close!

 

[pennychew]

Has anybody seen Doody Toody today?

 

[davesparks]

There can be only one possible cause for this......

Plumbers!

 

[tazz]

There can be only one possible cause for this......

Plumbers!

No it UKESrail (aka Essex again)........

 

[Knobhead]

He'll have been at a loose end in the afternoon

 

[sammyshooter]

Still going guys:

http://www.bbc.co.uk/news/uk-england-london-32157618

There have been surges all over central London, one knocked the till out in nandos when I was getting my tea last night, I was livid!

 

[Gardner]

I must ask, how are the 11kv MV networks earthed? Anyone know?

 

[Engineer54]

The same as LV networks, via earth electrodes....

 

[UKMeterman]

True, but there is often a neutral earthing resistor or similar at the star point of the upstream transformer.

 

[PEG]

...Watched the inferno on TV...looked a lot more troublesome than a standard PFC test...

 

[Engineer54]

True, but there is often a neutral earthing resistor or similar at the star point of the upstream transformer.

How far upstream are you talking about??

 

[Gardner]

The same as LV networks, via earth electrodes....

TT for MV? I mean the neutral point of the supply transformer. A high resistance or Peterson earthed neutral point will drastically limit fault current greatly reducing the incident energy at a fault. Solid grounding is something I would avoid in MV, even though the US does it like crazy because every other MV-LV transformer is wye-wye.

 

[Engineer54]

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.

 

[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!