How to explain this

[pwrtran]

Assume there is a resistive and inductive line, which means no capacitance considered. A 3phase short circuit occurred on the end of line, let's also assume the source is 1pu with 0 phase angle. My question is will it be possible that at some point along the line the voltage leads the source voltage and how do you explain this?

Thanks in advance!

 

[davidbeach]

Why do you think that it might?

 

[pwrtran]

davidbeach
To be honest with you, my first reaction is NO, there must be something wrong since voltage always tend to drop towards the downstream and there is no capacitors to cause leading too. But, I also asked myself - Why Not? It just against what I thought it should be...

 

[davidbeach]

You have a source voltage and a series of inductances and resistances. The voltage drives a current. You can find the voltage at any point in the circuit by subtracting the voltage drop of current through impedance from the source voltage. What characteristics would your impedance have to have in order to produce the results in your question?

 

[pwrtran]

I was trying to solve a 3-ph symmetrical fault of a double transmission line like this S=T=T=T=T=T=S "S" represents the source, "=" represents the double transmission circuit, "T" is the tapping DESN station. The condition is that the upper circuit is radial fed by the left end source and the right side end is open. The lower circuit is dual fed by both sources. Consider a 3ph fault on the lower circuit close to the right end source, breakers at both side of the lower circuit open to de-energize the line. However, the upper circuit can back feed the lower 230kV circuit through the tapping TS's via the secondary bus tie breakers. So, the reverse power flow protection or line distance relay kicks in to trip the bank breaker. I was using node analysis method and matrix to solve the fault current and the voltage of the interesting TS branch, however, I got some leading voltages at 3 nodes on the upper 230 circuit close to the left side source. Since I haven't practiced the matrix and the node analysis for a quite long time, I don't feel very confident of my result, and that how my questions came up. I plan to use the old way "delta-wye" and "wye-delta" transformation to simplify the impedance and compare the result. But, it will be whole lot work by working on the impedance conversion. Any ideas...?

Thanks!

 

[davidbeach]

Look at a per-unit per-phase model of the system. If you have the same phase shift from transmission line to transmission line across each station, you can ignore all phase shifts. Now you just have a network of impedances. Use your network reduction techniques to find a single equivalent impedance from each source to the fault, calculate the fault current, and then you can calculate the current and voltage at any given location. The other option is to model your system in a software package designed for that purpose and compare the results.