i didn't get the clear picture about what happens when these(above pic = 6 wires & no neutral there) high-voltage wires gets broken or fall to ground(even if not broken).
Maybe there is no one here with experience of high voltage power transmission lines who can give a clear answer, I have no experience in this area.
However when has lack of knowledge ever held anyone back here on ETO!
Some inspired guess work.
The voltages and currents will be monitored at varoius points in the network and transmitted back to the network control room via the telemetry system.
The guy in the control room will be keeping an eye on what is going on.
The network control computer will throw up an alarm if any voltage or current exceeds some predefined limit (high or low).
In the case of a complete break in a line, it will be obvious form the loss of volts at the end of the line which is broken.
What action will be taken as far as tripping and isolating the line is concerned, Who knows?
If a tower fails and the lines are on the ground but still passing power to the far end of the line, again there will be some telemetry from the remote end of the line which will indicate what? I guess it depends on the exact nature of the fault.
I don't know if overhead lines have an "Earth Leakage" measurement device, if they do, a sudden large increase in earth leakge current should be alarmed in the control room, where the operator will do? Who knows.
If the fallen line is reported by some member of the public who thinks that the world is about to end, again, who knows what the action would be?
I guess a first course of action would be to send the on-call line fault fixing guy to go and have a look to see what is really happening and report back to the network control centre where the engineer responsible for the network will make a plan to isolate and re-route around the faulty section (if possible) and send a repair crew to fix the problem.
Wow, for someone who knows nothing, I think I have just written half an operations manual for an electricity supply network!
So, did that rambling missive help your understanding?
JimB