Voltage Rise Due to Network Capacitors

[trchambe]

Hello all,

I am analyzing the effect of switching in various capacitor stages on voltage rise throughout a system (see the attachment). Looking at only one capacitor (say cap bank E at 6.3MVAR) and its effect on bus B, I calculate the rise by dividing the capacitor kVA by 100 (100MVA base), and multiplying it by the per unit impedance between the source and the first bus common to both cap bank E and bus B (which is Bus A in this case)

(6.3MVAR/100MVAR)*0.15 pu = 0.00945 V pu



My question is how would I determine the voltage rise on a given bus by switching both capacitors on at the same time? Do I need to use the Thevenin equivalent of the two feeders, or can I simply perform the calculation twice and add the results?

 

[PHovnanian]

The most accurate figure will be given by generating an equivalent network and solving for the rise at each point.

However, your example indicates that you will be satisfied with the simple approach. In this case, you can just add the delta Vs resulting from the total kVARs added times the inductive reactance through which it flows.

 

[jghrist]

I agree with PHovnanian. In your example, though, you use a per unit impedance of 0.15, but your diagram shows the impedance is 0.15 ohms, not 0.15 pu.

 

[magoo2]

I agree with the other 2 comments. It's simplified but still essentially Ic * X (or pu Ic * pu X), so it's correct.

Your diagram shows R and X. Assuming they are in per unit rather than ohms, you should be using just the X term, not the Z term. This comment will also apply to the 0.7 and 0.05 values when you factor in the other cap bank.