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Topic Title: Low voltage network (400V)
Topic Summary: Can anyone recommend some literatures about the low voltage networks in the UK?
Created On: 17 October 2012 02:50 PM
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 17 October 2012 02:50 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Hello everyone,

Currently, I am doing the research about the LV network in the UK. I wanna to find some information about the detailed technical information about the LV network,such as, how long is the LV mains cable, how many houses are connected to one redial LV feeder, what is the general capacity of a LV transformer etc. Based on these information, I want to build a low voltage network model for my work.

I am searching these information on the websites of DNOs in the UK. However, most are about the connection of customers, few about the details of the LV network. So could anyone recommend some literature about the LV network to me.
Many thanks!
 21 October 2012 09:14 PM
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ArthurHall

Posts: 735
Joined: 25 July 2008

The Electricity assosiation set of books that go with their "Power System Protection" course have a chapter that you may find relevent. Chapper 16 on the third volume covers urban distribution and looks at the protection of the different types of LV network.
 23 October 2012 08:29 PM
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cookers

Posts: 203
Joined: 10 February 2012

Swordlover this is a big subject, a whole career could be spent just trying to get a grip with this, so my best wishes are with you as you build your model.

If you want to understand the rational behind the LV network design architecture of the UK, you really ought to have a knowledge of the 11kV, 33kV, 132kV, 270kV, 400kV network architecture, protection etc.

I would concur that the Electricity Association is a good place to start.
 25 October 2012 05:21 PM
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iie71219

Posts: 2
Joined: 21 May 2007

If you want to understand the rational behind the LV network design architecture of the UK, you really ought to have a knowledge of the 11kV, 33kV, 132kV, 270kV, 400kV network architecture, protection etc.



Having spent 30 years as a Distribution Engineer with Eastern Electricity, ending as Shift Control Engineer in charge of the biggest Distribution Network in the western world I must say I have no idea what the 400kV, 275kV, 132kV, or 33kV networks have to do with LV Network design. LV Network design is basically an exercise in applying Ohm's Law once a decision has been made about the peak current calculated from the 'After Diversity Maximum Demand' (ADMD) of the consumers/customers to maintain the voltage within statutory limits. ADMD will vary greatly depending upon whether mains gas for heating and cooking is available or not. In the mid 70's 'With gas' 2kW was used; 'No Gas' 6kW, 'Electric Heating' was 'Heating Load + 2kW'.

I'll concede that as 11kV/LV transfomers only have off-load tap selection, the maintenance of 11kV volts by on-load tapchangers on 33/11kV transformers plays it part in the regulation of LV volts received by customers but going up to even higher voltage systems is unnecessary.

I've read many textbooks about Electricity Distribution Engineering, most of which are still on my bookshelf, but none deal with LV in any detail at all as far as I can see, other than a bit about HRC fuses, so cannot make any recommendations but I'll be happy to try to answer any direct questions about design philosophy, tapered mains, fault impedance etc...
 05 April 2013 09:19 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Dear Sir,

In some cases, two transformers are connected in parallel to enhance the reliability of the low voltage network; they may operate at the same time or only one transformer operates and the other works as a backup. So I want to know whether it is a common practice to connect two low voltage (11kv/0.4kv) transformers in parallel to improve the reliability of low voltage feeder?

Thanks for your attention!
 07 April 2013 08:49 PM
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alanjhodgart

Posts: 14
Joined: 11 September 2002

Swordlover

As has been stated already, LV mains design is an exercise in Ohm's Law, although sticking the maximum number of customers on a feeder without exceeding statutory voltage limits isn't the whole story. You also have to consider the number of customer's that will be affected in the event of a cable fault, i.e. splitting the main to limit this to a reasonable number etc etc.

In the Yorkshire area, the largest LV main that is now installed is 300sqmm. The largest transformer that is installed is 1000kVA.

With regard to knowledge of the upstream 11, 33 and 132kV networks, the main thing I think to be aware of is that putting two LV substations parallel may put a parallel on between two Primary substations and potentially two Grid Supply Points. LV parallels that do this are generally known in the area, however looking at the upstream network should quickly reveal this, if this is not possible the Regional Control Centre should also be able to give you this info.

Generally LV transformers are not run in parallel due to the increase in PSCC and also the increase in the number of customer's that would be affected in event of a fault.

Alan
 13 April 2013 04:31 PM
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broadgage

Posts: 1265
Joined: 07 August 2007

Many good points above, to which I would add that most real world LV networks are not really designed as such but "just sort of grow"

New small customers are often added without any detailed assesment of the effects on the rest of the network.
If voltage drop becomes excessive then it is common practice to either instal a new main and connect the larger loads to that, or to feed an existing main from each end, usually with dissconnecting links or fuses in the middle.
A new larger customer would normally be served by an LV main installed for the purpose, but which might later also serve other customers.
A very large customer, but still one served at LV, would normaly have a substation built primarily to serve that customer, but also used for other nearby loads.

LV cables are often limited to about 240mm or 300mm. If that is not enough then either a second main is installed with some customers on each one, or in the case of a single large customer cables are parraled.
 23 April 2013 10:26 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

Broadgage is absolutely correct.

The LV network in most places is pretty shambolic and has evolved rather than been designed. Connections are made using the lowest cost consideration until the circuit is overloaded; then new 11 kV substations will be cut in.
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