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Supersynchronous AC Electrical Motor

IP.com Disclosure Number: IPCOM000077636D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Gunn, JB: AUTHOR

Abstract

Most requirements for medium sized AC electric motors are fulfilled satisfactorily by conventional machines of the synchronous or squirrel-cage induction type. They have, among other advantages, a very simple form of construction resulting from the absence of electrical connection to the rotor. However, they have a limitation in that the rotor speed cannot exceed the supply frequency (e.g., 3600 r.p.m. for 60 Hz). Described is a synchronous motor in which the self-contained rotor, not much more complicated than a squirrel-cage, runs at twice synchronous speed.

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Supersynchronous AC Electrical Motor

Most requirements for medium sized AC electric motors are fulfilled satisfactorily by conventional machines of the synchronous or squirrel-cage induction type. They have, among other advantages, a very simple form of construction resulting from the absence of electrical connection to the rotor. However, they have a limitation in that the rotor speed cannot exceed the supply frequency (e.g., 3600 r.p.m. for 60 Hz). Described is a synchronous motor in which the self-contained rotor, not much more complicated than a squirrel-cage, runs at twice synchronous speed.

Consider two different wound-rotor machines, 1 and 2, each with a field assembly excited by a common polyphase supply of angular frequency omega(o), to give an n-pole-pair magnetic field pattern rotating at angular velocity omega(phi). If the rotor windings also correspond to n-pole-pairs, and are rotating at angular velocity omega(r), the normalized emf V induced in each rotor is

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A simple implementation is thus a 4-pole machine (n(1) - 2) interconnected with a 2-pole machine (n(2) = 1), to give a rotor speed equal to twice the line frequency. Notice that since the rotors are connected only to each other, and they rotate together, they may be mounted on a common shaft, with electrical interconnections rotating with the shaft. Thus, no slip rings or brushes are required. It will connected only to each other, and they rotate together, they may be mounted on a common shaft, with electrical interconnections rotating with the shaft. Thus, no slip rings or brushes are required. It will be seen that the rotor emf's and magnetic fields alternate at a frequency 3 omega(o) and thus higher- quality magnetic material is required in the rotors than in the usual induction- motor rotor.

A further simplification becomes possible when it is noticed that (provided magnetic saturation is avoided) the two wound-rotor machines are linear systems, but orthogonal in the sense that a rotor with a 2-pole winding does not couple to a 4-pole magnetic field pattern, and vice versa. Thus, the two sets of field coils, a...