Motor Generators

A motor generator is a device for converting electrical power to another form. Motor generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line. Large motor generators are used to convert industrial amounts of power while smaller motor generators are used to convert battery power to higher DC voltages.

In the context of electric power generation and large fixed electrical power systems, a motor generator consists of an electric motor mechanically coupled to an electric generator alternator. The motor runs on the electrical input current while the generator creates the electrical output current, with power flowing between the two machines as a mechanical torque; this provides electrical isolation and some buffering of the power between the two electrical systems.

One use is to eliminate spikes and variations in unstable or to provide phase matching between different electrical systems.

Before solid state AC voltage regulation was available or cost effective, motor generator sets were used to provide a variable AC voltage. The DC voltage to the generator’s armature would be varied manually or electronically to control the output voltage. When used in this fashion, the MG set is equivalent to an isolated variable transformer.

Motor–generators have even been used where the input and output currents are essentially the same. In this case, the mechanical inertia of the set is used to filter out transients in the input power. The output's electric current can be very clean and noise free and will be able to ride-through brief blackouts and switching transients at the input to the set.