How to find the line-ground current contribution from one branch?
I want to calculate the zero sequence charging capacitance based on known ground current contributions. That is, I know that some line A, B and C contribute 50A, 30A, and 10A respectively. Based on this, I want to enter the charging capacitance. My problem is that I can't figure out how to do this properly.
From literature, the equation for line-ground current in an isolated network is: If = Va*3*j*w*C / (1 + 3*j*w*C*R), where R is close to zero, thus |If| = Va*3*w*C. However, using the same B-value for different lines gives very different currents. It's even dependent on which side of the line the fault occurs.
Suppose I have the simple network below. If I try a simple line-ground fault at bus 3, with the dashed line out of service, I get a contribution I0 = 42.2A from bus 2. However, if I take the other vertical line and try a line-ground fault at bus 2, I get a contribution I0 = 31.2A from bus 3. I really don't see why this is.
Anyone know that might cause this, and how I can find the correct B-value? I use psspy.scmu to find the currents.
