Signals on power lines get filtered out by transformers, line reactors, capacitors, etc. they are also expensive to inject and extract since it requires high vo

Signals on power lines get filtered out by transformers, line reactors, capacitors, etc. they are also expensive to inject and extract since it requires high voltage connections which have to be of the same quality as the rest of transmission system components. I’ve worked both with power line carrier for transfer trip schemes and ripple plants for controlling hot water loads. More likely your ripple plant is going to have some failure resulting in tripping all your generation when it didn’t need to. Many Important plants and transmission lines are connected by a utilities own fiber which can be used to transmit the actual state of the system instead of trying to infer it from the power waveforms. This is the best solution but obviously expensive. Uncontrolled decentralized embedded generation is not meant to ever energize a dead line. If it has a solid state power electronics interface to inject power (a fancy inverter) it is probably operating in a mode where it follows the waveform on the grid to make sure it stays in phase. If the grid waveform is poor quality, full of harmonics due to faults, or phase shifts due to major loads or generation disappearing resulting in instantly changing power flows, the inverter can’t stay in phase. It is probably a delicate balancing act to be able to follow the grid frequency but also affect it by injecting active and reactive power. I’m not an inverter guy so this is mostly speculation from reading data sheets and manuals for grid tie small battery systems. Not sure about rocof tripping generation on falling frequency. There are situations in which injecting power in to an island can result in overvoltages that would damage all of the equipment on the island, so it is better to avoid it if it looks like an island might be forming. Just a guess based on experience with an embedded steam turbine. There could have been a very short increase in frequency for the 80ms or 4-5 cycles when the single phase to ground fault occurred as faults cause machines to accelerate since it is the same as removing the load and replacing with a short circuit. Otherwise the only increase in frequency was when it started to recover by the system operator calling for more generation.