The NERC advisory indicates that this fault had severely delayed clearing, 1.7 seconds. Several things happen... depressed voltages from the system feeding the fault cause real power consumed by the load to decrease drastically, which causes generation to accelerate. Once the fault clears, the rest of the system decelerates the rotors of the machines in addition to generation that trips on overspeed creating gen deficiency, resulting in the frequency depression. Hence the oscillation starts.
@zassounotsukushi Excellent question. According to a NERC advisory on this incident, the initial increase in frequency was due to a fault on a 138-kV line.
@PowerITLabUTK ok sure, that could make sense. Sorry for my shallow knowledge, but it seems plausible that the 138-kV fault caused a loss of load, which cascaded to a generator overvoltage or overspeed trip locally.
The 138-kV line might be past the Y-Delta connection that blocks zero phase current from the transmission backbone so asymmetric faults will loose load as opposed to add load.
Since this is widespread frequency data we wouldn't see the local behavior of the initiating events.
The NERC advisory indicates that this fault had severely delayed clearing, 1.7 seconds. Several things happen... depressed voltages from the system feeding the fault cause real power consumed by the load to decrease drastically, which causes generation to accelerate. Once the fault clears, the rest of the system decelerates the rotors of the machines in addition to generation that trips on overspeed creating gen deficiency, resulting in the frequency depression. Hence the oscillation starts.
thatspsychotic 1 month ago
If this is a generator trip, why does the frequency initially increase?
zassounotsukushi 3 months ago
@zassounotsukushi Excellent question. According to a NERC advisory on this incident, the initial increase in frequency was due to a fault on a 138-kV line.
PowerITLabUTK 3 months ago
@PowerITLabUTK ok sure, that could make sense. Sorry for my shallow knowledge, but it seems plausible that the 138-kV fault caused a loss of load, which cascaded to a generator overvoltage or overspeed trip locally.
The 138-kV line might be past the Y-Delta connection that blocks zero phase current from the transmission backbone so asymmetric faults will loose load as opposed to add load.
Since this is widespread frequency data we wouldn't see the local behavior of the initiating events.
zassounotsukushi 3 months ago