Calculte CCT with series capacitor transmission line.
Hi, folks. Recently, I asked quite lot questions. Here is another one.
I am trying to calculate critical clearing time (CCT) of branch-faults in system. But I got some problem whens I met transmission lines with series capacitor. Each of these lines, in my saved case file, is modeled with 4 bus, in which 2 are mediate bus, connected to 2 main bus by a negative reactance, and connected together by line impedance. I wonder in which we applied branch-fault for those lines, main bus or mediate bus, because the results were different. Also how we deal with transmission line with 1 series capacator?
Another question, because data for MOV (by-pass circuit) of SC isn't avaiable in my dyr now, so is it ok to set the fault impedance equal to value of line's SC capacitance?
Can't you just sum up the impedances of the line sections and remove those intermediate buses?
I want to have some room for MOV (which will be added later after we get data). Also, removing buses is time consuming and can make it difficult for some our other apps. But without MOV, it's a good choice to remove intermediate buses. Maybe I got to carried away bcz of MOV.
Just curious if results are significantly different when fault is applied on main buses or intermediate buses
Yes, it's significantly different. In some cases, faults on intermediate bus return infinite CCT. At first, I had no idea, but now I think in those cases, psse understands Series Capacator as a shunt capacitor (connected to the ground) and then system change from one to another steady state.
In the other hand, faults on main buses haven't returned any thing weird till now. but IMO, it will be more accurate if we applied fault on intermediate bus with MOV modeling, because the change in line impedance during transient will be the most similar to real behavior.