A device used to control the speed of a prime mover. A governor protects the prime mover from overspeeding and keeps the prime mover speed at or near the desired revolutions per minute. When a prime mover drives an alternator supplying electrical power at a given frequency, such as 60 Hz, a governor must be used to hold the prime mover at a speed that will yield this frequency. An unloaded engine will fly to pieces unless its speed is under governor control.