Droop speed control

It is commonly used as the speed control mode of the governor of a prime mover driving a synchronous generator connected to an electrical grid.

It works by controlling the rate of power produced by the prime mover according to the grid frequency.

In practice, the droop curves that are used by generators on large electrical grids are not necessarily linear or the same, and may be adjusted by operators.

The actual speed of the prime mover is allowed to "droop" or decrease with respect to the reference, and so the name.

[1] For example, how fuel flow is increased or decreased in a GE-design heavy duty gas turbine can be given by the formula,

Normally the changes in speed are minor due to inertia of the total rotating mass of all generators and motors running on the grid.

[3] Adjustments in power output for a particular primer mover and generator combination are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor or by an engine control unit adjustment, or the analogous operation for an electronic speed governor.

All units to be connected to a grid should have the same droop setting, so that all plants respond in the same way to the instantaneous changes in frequency without depending on outside communication.