Design of 20kV Distribution network in Djibouti

[shersan]

Hello all,

I'm planning to develop a suitable 20kV distribution network in an area of Djibouti to feed small industrial units and ware house located in a certain area .Max .load requirement of per industrial units is around 700kVA and small units requirements starts from 50kVA .

Total load power requirement of the total area is about 5.5MVA .

Djibouti EDD have HT distribution voltage level are 20 kV and agree to give two cable for our area network to form a
ring network .

My proposal in my mind is to strategically locate pocket substation consists of ring main units ( 2F +1 T ee off ) with transformer of 20/.4kV , 1500kVA/1000kVA/500kVA in a ring circuit formed by EDD 2 Cables.I presume the 2 cables can be paralleled as it's feeding from same EDD substation .

.Both the EDD incoming cables are connected to a 2F + 2 T RMU and from 2Tee off swiich with breaker protection feed the next located located 2F+1 T RMU indiviudually and so on the connected to a 4 or 5 more RMU's located different places

I would like to have your inputs on the following .

1) What kind of protection I need to consider in each Ring in Ring out Switches or the protection on the Transformer feeder .
2) I'm prefer to give an O/C protection and E/F indication on each RMU on the T -off unit and Ring IN and Ring Out will be Switches with SF6 insulated .


regards ,

Rana .

 

[RalphChristie]

Depending on costs.....

1. Direction protection on the Ring in Ring out feeders or some kind of cable differential protection.

2.On transformers of those size I would apply O/C and E/F protection, a Buchholtz relay and maybe a top oil temperature relay.

 

[RalphChristie]

Sorry

Correction: Directional protection

Directional protection would be the easiest and cheapest to apply, but due to grading you can have a time-factor/time-delay at the source.
Feeder differential protection can be fast (no time delays) but there have to be some kind of communication-link between two relays (at different sides of a cable) and that can add to additional costs.