I first came across this phenomenon with the Kosovo issue mentioned elsewhere. But it immediately made sense to me from driving a gas car (you don’t notice it i

I first came across this phenomenon with the Kosovo issue mentioned elsewhere. But it immediately made sense to me from driving a gas car (you don’t notice it in an electric): hold your foot on the gas pedal without moving it and go up a hill. What happens? The engine RPM go down and also the car slows down (because it depends on RPM to the wheels). As the load increases, without more power (fuel flow) the engine slows down. Same with an electric generator/motor: if you pull power off more than it’s being driven, each push from the driving field is less than enough for the rotational rate, so the rotation is slower, and thus the frequency too.