About a "stabiliser"?

Quite often, in a rural environment, you will spot a different looking transformer on a pole. Thesr are in place in an attempt to keep a constant voltage on a line. They work by running a current controlled tap in the transformer. When the current goes to a certain level, engineering predicts that the voltage will droop to a certain level. The tap chosen will provide a higher voltage to the powerline. As the load is shed, the lower current drawn will move the tap to supply a lower voltage to the powerline. Engineering and sampling provides information on the transformer to be chosen and the range of taps needed. As long as the primary can supply the correct number of watts, operation is observable as decrete jumps or dips.