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Multiple Capacitor Bank Switching at 66 kV

Multiple Capacitor Bank Switching at 66 kV

Multiple Capacitor Bank Switching at 66 kV

(OP)
Hello,

I am working on a switching 10 MVAR bank in steps of 4 and each step is 2.5 MVAR. I am using PSCAD for my study. IEEE Standard C37.012 provides description on switching back to back capacitor banks. It does say that results won't match the simulation in case I try to use the formula for multiple capacitor bank switching when two banks are switched in and adding the third bank,. The inrush currents from the PSCAD simulation are lower than the computed with the formula from the standard.

One important point I noticed, for case with isolated switching and back to back switching the current in the steady state after the cap bank is switched in should matach the steady state current when only one bank is switched in. For example.

Source is far from the cap bank location 150 kM, Lightly damped system as not much resistance is present in the system.  
Q=2.5  mvar Three phase
inrush reactor L=2.5 mh
Q/perphase=0.83 MVAR, c=1.51622 micro farad
v=66  Line to Line

I=22 amps

10% Harmonic content , 10% overvoltage factor m 10% for postive tolerance for capacitance.

I =1.33*22= 29Amps


Once one two or three banks are switched in all the current should eventually return to a value closer to 29 amps or as more banks come in parallel and impedance changed, the current should change.

Any problems that 5th harmonic could create in the system.  

RE: Multiple Capacitor Bank Switching at 66 kV

Is there a question being asked?

Is this a homework problem?

RE: Multiple Capacitor Bank Switching at 66 kV

(OP)
Hi

This is not a homework problem. I am asking about the practical aspect of cap bank switcing, when multiple banks are switched against one bank. IEEE standard does not talk about the authenticity of therotical results when computing inrush currents.

I wanted to know if anybody has experience with multiple cap bank switching and could provide some input.

Thanks

RE: Multiple Capacitor Bank Switching at 66 kV

There should be a lot of reference data available on-line regarding back-to-back cap bank switching.

I would be surprised if PSCAD simulations will help you really determine precisely what will happen, unless you have a pretty sophisticated model to work from.  

 

David Castor
www.cvoes.com

RE: Multiple Capacitor Bank Switching at 66 kV

A 10 Mvar bank at 66 kV seems very small to me.  Also 150 km of line should have enough resistance to provide damping.  Both of these lead me to believe it's not a realistic situation.

Start with initial energization of 2.5 Mvar against the system impedance.

Next go to second stage.  Switch 2.5 Mvar plus inductor to what is already energized at the bank.  Get inrush from system to the 2nd block of capacitance plus inrush from the first increment.

PSCAD should be able to handle all of this.  You haven't really presented any results on which to comment.  Certainly you might not match what you get from IEEE C37.102.  Assumptions may be different.  Did you assume any tolerance on the capacitance?  Did C37.102?  Ditto for source impedance.  Did you model the line as fixed or distributed parameter representation?

I've done enough of these simulations over the years with ATP that I'd encourage you to take a simple case and make sure you understand the results before going on to step 2, 3 and 4.  It's not rocket science.  

RE: Multiple Capacitor Bank Switching at 66 kV

(OP)
Thanks for your input Magoo.

It is a radial feed to a station with already voltage problems in the area. I agree with you that 174 km(my mistake it is not 150 km) long line should have enough resistance to damp the inrush oscillations. I see the presence of enough resistance because of enough voltage drop along the lines.

One questions, I am having some trouble trying to understand. When ever  I am doing a switching event with one bank, two banks or three banks in, it is always the "C" phase with the largest amount of current contribution. I did fault discharge current analysis and applied a fault before the main breaker and from all the four banks below, the "C" from all the bank had the largest contribution and it did not match the b and c phase current.

Please see the attached pdf document
http://files.engineering.com/getfile.aspx?folder=4fde65f0-7df1-4aad-89e3-ac7b57d791e6&file=cap1.pdf

Could u pleas provide some input. Thanks

 

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