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0 pointspjc5011mo ago0 comments

Frequency is effectively more important than voltage. Or rather it collapses first. Frequency reduction for a rotary generator means that more energy is being taken out than the rotary shaft energy is being put in, so it is effectively an early warning that voltage is about to drop.

Frequency coordination is absolutely critical, via phase coordination. A large generator must not get significantly out of phase. So frequency going out of spec triggers the generator to "trip" (disconnect).

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immibis11mo ago

As I understand it, it's not possible for a generator to get out of phase with the grid. Sudden changes in the grid phase instantly and catastrophically break generators, power lines, transformers, and so on, but that can only occur when you connect two grids together without synchronizing them. Which implies there are two separate grids to connect.

I don't know what specific threat is addressed by tripping generators offline when the frequency deviates by 1 Hz. Are they so mechanically fragile that is already damaging to them, or is it a precautionary measure because that kind of instability is likely to precede sudden frequency or phase jumps that are damaging?

mschuster9111mo ago

> Are they so mechanically fragile that is already damaging to them, or is it a precautionary measure because that kind of instability is likely to precede sudden frequency or phase jumps that are damaging?

Both actually. A frequency mismatch between what the grid has and what the turbine is supplying causes significant thermal losses, so you got to trip the generator anyway rather sooner than later, but a significant frequency deviation is always a warning sign that something is Massively Broken and requires immediate attention to find the cause - too low a frequency means you need to shed load immediately, too high means you need to shed generator capacity immediately.

tonyarkles11mo ago

Yeah, I think it really helps to think about the grid as basically one giant spinning machine. Everything is connected with wires instead of driveshafts, obviously, but a low frequency means that all of those machines that are burning fuel to try to spin at the right speed can’t generate enough torque to spin the rest of the machine at the right speed. And on the other side, spinning too fast means that all of the machines are burning too much fuel and need to slow the heck down right now (which can be hard to do with, for example, nuclear).

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applied_heat11mo ago

There is no such thing as a frequency mismatch between the grid and the generator. There are frequency deviations from 60 Hz but turbine and grid deviate together

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