All modern power systems have automatic start and monitoring systems incorporated into their control systems. On sensing either a failure of one or more phases or the line voltage falling below a predetermined level, as in a “brown-out,” the generator will start automatically. An automatic transfer relay will then switch from the incoming mains to the output of the generator. Usually, the length of time between generator start-up and the actual switchover is adjustable. That allows the generator to warm up a bit before accepting the load. In some applications, this time delay is necessary to allow the load to stabilize before the switchover takes place.

If synchronous motors are in use, applying full line voltage out of phase with a motor’s instantaneous electrical phase position can place destructive loads on the rotor. To avoid that, it is better to let the system come to a complete halt and then restart from scratch. Thankfully, that is usually not a problem with the normal induction motors found in broadcast transmitters. Even though that may be the case, letting the generator have a few seconds to stabilize before switchover is still a good idea. The start-up itself is fairly routine on newer systems. In cold parts of the country, the engine is normally heated, either by an engine block heater or by a combination of engine block and oil heating. With a good diesel engine, that means the actual start will be almost instantaneous. Of course, the motor-generator system is protected at several levels and may even be shut down if the monitors detect errors such as low oil pressure, over temperature, etc.

One standby power plant recently viewed by the author consisted of a generator bolted to the floor in the utility room of the station. A shaft with a universal joint was routed through a hole in the wall. In a lean-to type of shed attached to the back of the building was an old international model “M” farm tractor with the power take-off attached to the other end of the shaft. In the case of a power failure, the on-duty operator simply would go out into the back room and fire up the tractor, engage the power take-off and open the throttle. Once inside the building, he would operate a big manual transfer switch. While it might have been crude, it was inexpensive, and it worked very well. A little trickle charger was used to keep the battery on the tractor full and the tractor was started once a month and run for a little while to keep it ready to work.