Electromechanical Medium-Frequency Generator

an electrical machine, chiefly single-phase, that generates a current in the frequency band from 100 to 10,000 hertz (Hz), and occasionally higher, and is used primarily as a power source for induction heaters and ultrasonic and transportation equipment. At frequencies of up to 500 Hz and at high power (500 kilowatts or more), ordinary salient-pole synchronous generators with an increased number of polar pairs are used. For higher frequencies, especially at low power, only induction generators are manufactured. Depending on the design of the magnetic system, a distinction is made between homopolar and heteropolar induction generators. Homopolar generators (also called like-pole, ring-type, or longitudinal-field generators) have an AC field winding (in the form of a ring placed between the toothed packets of the stator) and an operating winding, which is mounted in the longitudinal slots of the stator. Each stator packet and rotor gear rim in such machines is magnetized around the entire periphery with a polarity of the same sign. Heteropolar generators (also called unlike-pole, segment-type, or transverse-field generators) have a field winding and an operating winding that fit into the longitudinal slots of the stator. The number of magnetic poles of alternating polarity around the circumference of the stator bore in such machines is equal to the number of slots in the field winding. The periodical component of the current induces a variable electromotive force in the operating winding at a frequency f = Zn/60, where Z is the number of teeth on the rotor and n is the frequency of rotation in rpm.

Medium-frequency generators most often have an asynchronous drive. At a power level of up to 200 kW the generator and motor are generally housed in a single casing on a common shaft, forming a one-unit frequency converter. Converters up to 100 kW in power are often made with a vertical shaft, since this greatly reduces their dimensions. Above 200 kW the generator and motor are manufactured separately and mounted on a common frame, forming a converter unit.