LV Distribution Feeder Queries

[Squire1998]

Hey there everyone,

I'm currently an EE student doing my 4th year project. As part of my project, I am carrying out a literature review into the design rules DNOs apply to their LV distribution networks.

I am trying to built up a reasonable understanding into how these networks are laid out. From what I can gather, most areas have a centralised substation with 5 or 6 parallel, radial feeders coming from the LV side of the transformer terminals to domestic and commercial properties.

I've done a bit of research already but I'm struggling with a few things I hope somebody could help clear up. I've included a picture showing one of the networks I'm studying:

• Where the red triangle is the secondary substation, am I right in saying that this network has two "main" feeders (red and blue).
• If that is the case, how are the branches physically tapped off the main feeder? For instance if a residential property is only requiring a single phase supply, how is that taken from a three-phase - 3/4 core cable? Is that cable taken into a junction box of sorts, or would it just be "tee'd off" directly from the main feeder?

Hope these questions aren't too silly and make a lick of sense

 

[davesparks]

The terminology as far as I know is 'distributing main' for the cable coming from the substation and down the street.
'service cable' for the cable which is tapped off of the distributing main to feed a customer.

Small services are generally tapped off directly from distributing main via line taps/ c crimps, pole top joint box if overhead or via a sealed underground joint if underground.
Underground joints are usually either cast resin, heatshrink or cold shrink types depending on the particular DNO, type of joint or operational requirements.
Larger services may have a feed directly from a feeder pillar at the substation.

 

[Pete999]

The HV Sub station will normally be formed by an open Ring, with an incomer HV an HV Local feed to a HV.LV TX and an outgoing HV feed to the next HV sub station,ere this method will be relocated, the Local feed to the TX will be HV transformed to LV, the LV feed usually goes in TP and N to a LV Feeder pillar, for example close by to a Housing development or similar large customer, TP and N as well as SP and N supplies are taken from the Feeder Pillar, suitably fused of course ( my knowledge of this has been from acting as an Authorised Person (Electrical) on military HV rings and HV Spurs) things may have changed, some authorities operate a closed Ring.

 

[Carl S]

Have a look on UKPN's website.

 

[Squire1998]

Many thank for the replys guys, all very helpful. They have cleared up my understanding a little bit.

Have a look on UKPN's website.

Cheers, I have gotten most of my information there so far but some of it wasn't clear enough for me to understand.

 

[Pete999]

Many thank for the replys guys, all very helpful. They have cleared up my understanding a little bit.


Cheers, I have gotten most of my information there so far but some of it wasn't clear enough for me to understand.

What part aren't you clear on?

 

[Squire1998]

What part aren't you clear on?

Sorry, I meant I wasn't clear with how the UKPN described how the service cables physically tapped off from the main feeder but it's been cleared up here.

 

[R-fur]

I does seem a bit strange at first, having a 25mm service solid tee'd off of a 300mm main fused at 400A. But remember the 400A fuse is to protect from earth fault or short circuits. The 100A fuse at the cutout protects the service cable from overload.
The earth loop impedance at a TNC-S cutout has to be below 0.35 ohm so the loop impedance at the main is easily low enough to blow the 400A fuse.