Feeder Reactor

[Timmy76]

Hello All,

I have a 115/24 Kv station with two Banks 60 MVA each and there are feeders going out of the station. Each feeder has a feeder reactor precceding a 25 kAmps breaker. The 3 phase fault level at the Bus with 2 banks tied on 24Kv side is 15KAmps. This is less than the 25 kA breakers rating on the feeders.

My question is

If I remove feeder reactors and rather put reactors on the Bus, that would also protect the feeders as there is a breaker with 25 kAmps rating.

Thanks

Timmy

 

[dpc]

If all of the circuit breakers are adequately rated for the full fault current, the reactors are probably not required. But apparently at some point, someone thought they were needed, so you might want to double-check your calculations and assumptions. Fault current levels usually increase over time, not decrease. Have you looked into the equipment at the other end of these feeders?

Also, I'm not clear by what you mean by "put reactors on the bus".

 

[Timmy76]

I meant by "putting reactors on the bus" is to have OR Shunt Reators at the Bus. May be with this fault current I don't need Shunt reactors at the Bus.

Please comment

 

[davidbeach]

Shunt reactors don't help you out with fault duty. Series reactors can limit fault current, but not shunts. Shunt reactors would be used for voltage control.

 

[pwrtran]

I=U/sqrt(3)*2Pi*f*L
How big the inductance of the in-line reactor? You may blow up the bus!

 

[wroggent]

Does '60 MVA Bank' mean bank of capacitors, i.e. shunt compensator? The purpose of the shunt reactors would probably be to lower the voltage during light loading conditions - they are essentially unrelated to fault current, as davidbeach said. The reactors are probably on the same side of the breakers as the compensators because it provides a path to ground for the compensator if the breaker is opened. If you move the reactor, and the breaker is opened, then a charge (high voltage) will be isolated on the feeder; this is a danger for line workers.

 

[Timmy76]

Sorry about the confusion,these are 60 mva transformers and series reactors create a high x/r ratio
I am trying to figure out how to calculate feeder reactance value to limit fault currents

 

[davidbeach]

You need to be using a system modeling program that does breaker rating analysis. Fault current alone can only be considered below some value of X/R established in the relevant ratings. Generally by the time you have too much current, your X/R is also above the standard value and it is forcing a further derating. You may or may not be able to achieve anything by adding series reactors; but even if you can you will only be able to go so far before the increasing X/R swamps out the decreasing fault current.

 

[Timmy76]

Main probem is our utility trying to Parallel all 4 ,115/24 kV 8%impedance, 60 MVA Tranformers with tie breakers closed. The only way to reduce current is increase transformer reactance and voltage drop for a fault might not be a problem as it is a stiff system with banks paralled. But for a differential fault on the BUS, IsquareT rating of the Bus dictates how long bus can take the fault. The cable egress out of the station is rated for 12 kV and fault outside the station is high enough to bring cable in to damage zone.

Please provide some input, how can we still parallel and still limit our breaker ratings.

 

[davidbeach]

You want the impossible.

 

[Khalid1970]

Series reactors used to limit fault current.

Various combination for reactors can be applied such as feeders, coupler, etc...


I have read an article before by trench (manufacturer) about this issue and it contains a lot of examples.

http://eepublishers.co.za/images/upload/Energize_Oct09/022_TT_Short-circuit.pdf