Why does disconnecting the receiving end of a transmission from the sending end increase the voltage at the receiving end?

Question

Some background information:

I have a transmission line circuit (included below). The rated voltage is 63.639kV and the rated current is 325A. The characteristic impedance is 30.3 Ohms. I also have inductance, capacitance, and speed. The line is fifty kilometers long.

After the switch is opened, disconnecting the receiving end from the sending end, the voltage at the receiving end is 73kV and the current from the sending end is 325A. After 272us (T), the voltage at the receiving end doesn't change, but the current is now -325A. After 544us (2T), the voltage at the receiving end is 53kV, and the current at the sending end is still -325A.

Why does the voltage increase when the circuit is opened, but then decrease after 544us but not after 272us?

Why does the current change from 325A to -325A after 272us and not immediately after the switch is opened?

What is the relationship between voltage and time?

What is the relationship between current and time?

It's a transmission line, so waves traveling on it and reflecting from the ends are the appropriate model. First, calculate how much time it takes for a wave to propagate from one end to the other. — John Doty, Nov 29 '23 at 14:36
Please supply all the information if you want an exact answer. L/m, C/m R/m, G/m, RL and Rs. I guess you may not have studied transmission-line theory? — Andy aka, Nov 29 '23 at 14:52
I don't want just the answer to this problem. I want to understand the concepts and formulas behind it. The exact values shouldn't be necessary. — AlienChicken, Nov 29 '23 at 15:10
The answers here might provide some insight: Transmission line reflection. I would like a non-mathematical explanation — Dave Tweed, Nov 29 '23 at 16:22

score 1 · Answer 1 · answered Nov 29 '23 at 14:31

Why does the voltage increase when the circuit is opened, but then decrease after 544us but not after 272us?

The voltage increases when the circuit is opened, because of the inductance of the wire. The inductance of the transmission line increases the voltage. The voltage doesn't decrease for 544us because of the capacitance of the transmission line. Capacitance indicates the ability of the transmission line to store voltage and current. It stores the voltage the increased voltage.

Why does the current change from 325A to -325A after 272us and not immediately after the switch is opened?

The current drops because the switch was opened. When a circuit is opened, the current flows in the opposite direction. We represent this change with a change of sign.

Why does disconnecting the receiving end of a transmission from the sending end increase the voltage at the receiving end?

1 Answers1