Motor–generator

Low-powered consumer devices built before 1933, such as vacuum tube vehicle radio receivers, did not use expensive, noisy and bulky motor–generators.

Instead, they used an inverter circuit consisting of a vibrator (a self-exciting relay) and a transformer to produce the higher voltages required for the vacuum tubes from the vehicle's 6 or 12 V battery.

The DIII-D tokamak at General Atomics, the Princeton Large Torus (PLT) at the Princeton Plasma Physics Laboratory, and the Nimrod synchrotron at the Rutherford Appleton Laboratory each used large flywheels on multiple motor–generator rigs to level the load imposed on the electrical system: the motor side slowly accelerated a large flywheel to store energy, which was consumed rapidly during a fusion experiment as the generator side acted as a brake on the flywheel.

In addition to the above specialized applications, flywheel-generator systems have been commercialized for use in data centers as an adjunct or alternative to more conventional battery or generator-based uninterruptible power supplies (UPS).

Alexanderson alternators produced RF up to 600 kHz, with large units capable of 500 kW power output.

While electromechanical converters were regularly used for long wave transmissions in the first three decades of the 20th century, electronic techniques were required at higher frequencies.

The output's electric current can be very clean (noise free) and will be able to ride-through brief blackouts and switching transients at the input to the MG set.

If the speed loss is excessive (the power outage is too long), the re-closure current will trip the protection circuit-breakers, resulting in a shut down.

Motors and generators may be coupled by a non-conductive shaft in facilities that need to closely control electromagnetic radiation,[5] or where high isolation from transient surge voltages is required.

The low voltage output charges the streetcar's batteries and supplies current for control and auxiliary equipment (including headlights, gong ringers, door motors and electromagnetic track brakes).

[citation needed] A useful feature of motor–generators is that they can handle large short-term overloads better than semiconductor devices of the same average load rating.