Pilotwire protection using Translay Relay SDPS102 & 103 1

[shersan]

Dear All ,

Please enlighten me with some good solutions .

In our 11kV electrical distribution systems ,Five nos of 11kV substations(connected as Ring ) are fed from 2nos, 800 A feeders of 33/11kV primary substation . The ring in & ring out cables are 2 Runs of 3cx 185 sq mm PILC/Al cables and all switchgears are almost 20years old . Ring in Ring out feeders on 11kV substation are protected with only pilot wire protection with translay relays .Now the utility decided to change the incoming cable with 1 x 240 Sq mm XLPE/Cu cables inplace of 2 Nosof 3cx 185 sq mmm PILC and we might need to change the protection relay with normal MICOM P121 realy ( E/F & O/C)in place of translay relay on our 11kV S/S due to the source (utility ) substation feeders are protected with VA Tech DCD O/C & E/F relays .

As the 33/11kV ,2 feeders are sharing the whole connected load on our 5 nos 11kV S/S , what kind of protection realay at the incoming point of these 5 S/S ' s is advisable ???? The ring is connected in the following sequence . 33/11kV ( feeder 1 )ring in to S/S -to S/S 2 to S/S 3 to S/S 4 to S/S 5 to 33/11kV ( feeder 2 ) .Mostly all connected loads crane loads .Supply continuity is paramount in the event of fault in any of the 5 S/S's .

 

[DiscoP]

I would be using directional overcurrent protection on the two incomers, especially if no instantaneous protection is to be applied on the incomers.

I would also have a non-directional oc/ef relay on the breakers each end of the ring, with translay on the feeders around the ring.

Ideally there would also be some form of busbar protection on each of the five substations, as a bus fault is not cleared by translay protection.

If no busbar protection is installed, the fault is cleared by both non-directional oc/ef relays at each end of the ring and the whole plant is lost.

This would cost a lot more, and would have to be balanced against the impact of a complete loss of power until the faulted bus is located, and also against the likelyhood of a busbar fault developing.

 

[shersan]

Thanks DiscoP

As we are thinking to get rid of pilot wire translay protection due to no guarante on the existing pilot wire , I feel the better idea is to have directional relays at the incoming feeders of all substation and the same provided at the 132/11kV S/S End .

Would it be a best protection scheme with O/C & E/F directinal realys at the source end and incomer of the 5 S/S's and then the non directional featured realy ( O/C & E/F realy such as MICOM P121 ) at the outgoing feeder ( load is crane load ) ????

My next wories is how could I grade the Upstream S/S ( 132/11kV ) with our all 5 down stream substation as it is formed as a ring . What should be minimum grading margin should be given between each substation Incomers and outgoing feeders .????

 

[DiscoP]

You could use directional o/c relays around the ring rathern than translay protection, although this means 5 grading steps under the utility and above the crane load currents - it could be quite difficult but is not as big a problem with translay protection.

I like to have 300ms as a grading margin, although sometimes it is necessary to use a lower margin - the Areva NPAG available on their website give some guidance on this.

 

[shersan]

Thanks DISCOP,

I would use directional O/C& E/F relays (Eg : CDG relays ) at the ring in & out feeders of the each substations and non directional featured O/C & E/F relays ( Eg:MICOM P121 ) for the outgoing crane feeders of the each substations .And the 132/11kV feeders ( 2Nos ) at each end with non directional relays . Please note that all 5 S/S would be on a ring circuit and in case of any fault in any of the S/S s(11kV ) ,one of the feeder will take care of the load without any power interruption .


Lastly but the least can you describe what was the benefit of having pilotwire protection given earlier ..
and could you refer me some web pages which could help me to improve my knowledge in relay protection .

 

[DiscoP]

The main advantage of Pilot wire protection (Translay) is that it doesn't require any time delay as it only operates for a fault on the feeder being protected - so less grading steps are required.

The downside of this protection is that no back-up for faults on other feeders is provided.

Protection Relay Manufacturers websites might be a good place to start for information.

A good page to use with links to nearly all manufacturers is

http://home.att.net/~john.horak/

Also - please note that the CDG relay is non-directional - they are the same type of protection as the P121. For directional protection you would need to use CDD or P127 if using relays from GEC/Areva

 

[RalphChristie]

I think DiscoP has given you very good answers.

You can find the NPAG-manual at (free download):

http://www.areva-td.com/static/html...typid=1107432285131&productline=1079943326752

(copy and paste whole address)

For directional protection:
Download chapter 9 (Overcurrent and earth fault protection), read from pg 12.

For feeder differential protection (translay etc.):
Download chapter 10 (Unit protection of feeders)