RCA of overvoltage 132kV line tripping

[Subhan7]

Hello all,
I am a recent electrical engineering graduate, currently given the role of a power system operations engineer.

We have a 100 MW generation, with two outgoing circuits connected to a 132kV grid. The length of the circuit is 100 km each. During the shutdown of Line-1, at first, breaker at the grid end was first opened. At the generation side, Line-2 tripped on TOV (time delay overvoltage), the disturbance record from relay gives information that phase voltages rose up to 95kV.

I can't figure the reason that led to such high overvoltages since it's a medium transmission line and Ferranti effect is still not that much appreciable.

Another thing is that relay picked at the grid end is 'distance trip- CB close-closing block' and 'carrier received'. How the relay sensed overvoltage as a fault and does overvoltage protection can be used in inter tripping with other relays (like distance tripping in our case)?

Please help me analyze this tripping case, thank you.

 

[davidbeach]

You need to have the settings of every relay that did anything and every relay that might have done something but did nothing. Then you need all of the relay event reports. What were the flows at both ends of the line? Large voltage gradients are possible under odd-ball conditions.