Advantages of Double Circuits in Availing Power Supply

Is the other one standby??

It is a 100% rated 110KV, 50 Hz dedicated double circuit feeding our plant alone.

send a single line diagram. We will look in to that.

I'm certain that there can be other advantages.

Excuse me for doubting you but 110KV is a lot of voltage. I believe it is more likely a power grid distribution voltage that happens to be running through your facility instead of two 110kV lines powering your facility.

If both lines are paralleled normally, line voltage drop is reduced. Line current is less, less heating and longer life for conductors.

Sir,

I'm not an EE, but can suggest at some reasons for this common practice:

1. Dividing your load into two incoming feeders gives a substantial reduction in conductor size because of the pronounced skin effect and heat buildup problems with larger currents in the conductors.

2. Dividing your load will allow a wider selection of switchgear components and can reduce the available fault current to values that are easier to protect.

3. If one feeder fails, critical and essential plant loads can be switched to the remaining feeder via tie breakers, while other loads can be shed or shut down. This can be done with protective relaying in the switchgear or manually by (trained) operators.

4. The utility might supply both feeders from a single transmission line circuit, but has the option of moving one or both to a second transmission line circuit if needed to balance their load and/or handle transmission failures.

5. The utility might have a limit on the amount of power it can supply from a single transmission line, so more than one feeder would be required to spread your load onto multiple utility sources.

I remember reading a few decades ago about a pump station on the California Aqueduct, where the water was being boosted over the mountains south of Bakersfield. To start the first very large pump (80,000hp or 60MW) they had to parallel at least 4 utility feeders. Starting the rest of the 14 pumps was made a little easier because the running pump(s) supplied some of the inrush current. On the other side of the mountains they ran the water through hydro generators to recover a portion of the pumping energy costs.

Dear Mr. jmueller, Thank you sir, for your valuable points. But i disagree with your point no. 2 wherein you mentioned that the fault current will reduce. Actually, I think fault current will increase when we have parallel circuits since the impedance of the network get reduced in parallel circuits. please correct me if i am wrong. I am mentioning about 100% rated feeders, let us say a 10MVA load being feed from 110KV double circuit each feeder capable of supplying full load. hence load sharing is not the issue. Both the feeders are tapped from the same Electricity Board Feeder hence it is not actual synchronisation. We are only closing the Bus coupler at our end making it parallel. I agree continuity of supply is maintained when one of the feeders is tripped. Hence redundancy is there.

Sir,

Your reply is appreciated. I suggested a potential reduction in fault currents under the assumption that the two feeders did not have a parallel connection on the load side. If they are fed from different transformers on the supply side and not in parallel, I would expect a reduction in fault current. If they are both tapped from the same transformer, the available fault current might be reduced slightly, but if they are paralleled on the load side then your comment is valid.

When you spoke of parallel feeders, I was reading this to be two sets of feeder cables, with each set terminating in separate sets of switchgear. If you were referring to the common practice of running two sets of feeder cables from a single source to a single disconnect, then I totally misinterpreted your original question when I made my reply.

Thanks--JMM

Dear Mr. jmueller, Thank you very much for your valuable comments.

Pls, can you help us by giving a breif information about your plant (Load system), and your grid connection ( Source system ).