Abstract :
That an induction motor could act as a generator and return power to the line when driven at a speed above that of synchronism, has been known for many years. It has, however, always been regarded as more or less of a scientific curiosity, and except in the case of the Swiss three-phase mountain roads, where the motors are sometimes allowed to run as generators to brake the train on descending heavy grades, the non-synchronous generator has had but few commercial applications. The fact that the characteristics of this generator are such that it must receive a lagging current from the system, the magnitude of which is for a given machine definitely decided by the slip of the generator above synchronism, combined with the fact that when connected to a circuit is has no definite voltage and frequency of its own, make it lack the flexibility of the synchronous generator. In 1895, Mr. B. G. Lamme proposed running a non-synchronous generator with an unloaded synchronous motor, the generator to supply the watt component and the motor the wattless component of the current in the system. But though this suggestion rendered the non-synchronous generator a practical machine, it is easily understood that on account of the lesser flexibilities when compared with the synchronous generator, it has not appealed to the central station engineer as a desirable addition to his equipment.
