When is a "Repulsion Motor" NOT a Repulsion Motor?

According to its manufacturer at http://www.motcointernational.com/repulsion.htm
this is a present-day repulsion motor, rated 0.75 kW, 2880 rpm, 230V 50Hz single phase

The short answer to the question posed in the title above is "whenever it is the so-called 'repulsion motor' described by all orthodox sources".

I'll now go into some detail to establish that answer.

Definition

There is an electric motor design well-known to orthodox technology as a "repulsion motor". Searching on-line, or in electrical technology textbooks, we most often find definitions such as the following, from Alternating Current Machines, M. G. Say, 4th Edition, Pitman Publishing, p504:—

Repulsion motor

This is a form of series motor with the rotor energized inductively. The rotor winding is designed for a low working voltage, and its brushes are joined by a short-circuiting connector to provide a closed current path. The brush axis is displaced from quadrature with the stator d-axis so that the induced rotor current can develop interaction torque. When the motor spins the d- and q-axis fluxes have a phase displacement, developing a crude travelling-wave resultant of "elliptical" form. At a rotor speed corresponding to the synchronous, a nearly uniform travelling flux wave is attained, so that the commutation conditions are relatively good.

A better definition

This sort of definition is OK as far as it goes, but it gives no indication of why this machine is called a repulsion motor. Only much more rarely, in textbooks at least, do we find a comprehensive, honest definition and description such as the following, from Theory of Alternating Current Machinery, Alexander S. Langsdorf, Tata McGraw-Hill Publishing Co Ltd, 9th reprint 1985 (my emphasis at the beginning and end of the first paragraph):—

15-10. The Repulsion Motor. 

     The qualifying adjective employed to designate this type of motor is a hopeless misfit, but the term has been in use for such a long time that it is generally accepted. It appears to have been used for the first time in the specification of U.S. patent 363,185, issued to Elihu Thomson in 1887, to describe the machine shown in Fig. 15-18a, and in modified form in Fig. 15-18b. 

Fig. 15-18. Elementary repulsion motor of Elihu Thomson

The distinctive feature of this machine which differentiates it sharply from the types now in use is the open-circuited armature winding; the individual armature coils of Fig. 15-18b successively experience a torque when they are short-circuited by the pair of brushes displaced from the axis of the stator winding, the direction of the torque being in the direction of the brush displacement. It is perfectly clear that such an arrangement as Fig. 15-18a or b will not develop torque if the brush axis is in the plane of the stator coil, for in that case the active rotor coil constitutes merely the short-circuited secondary of a transformer linking with the stator flux; and if the brushes are displaced by 90º, there is likewise no torque since there is then no rotor current. It is only in intermediate positions of the brushes that torque is developed. But it is to be noted that if the brushes are in the plane of the stator coil, and if the plane of the active rotor coil is parallel to, but slightly displaced from, the stator coil, there will be a force of repulsion between the coils acting in the direction of the displacement; this is in accordance with the experimental fact (discovered by Ampère in 1820) that parallel conductors carrying currents in opposite directions repel each other, this phenomenon being utilized in the constant-current transformer described in Art. 2-27. It is probable that this particular behavior of parallel coils gave rise to the term "repulsion" in connection with the motor of Fig. 15-18, but the genuine repulsion between parallel coils has nothing whatever to do with the operation of the so-called repulsion motor.

Fig. 15-19. Connections of singly fed repulsion motor

     Whatever its origin may have been, the phrase "repulsion motor" is used to designate the arrangement shown diagrammatically in Fig. 15-19a. It consists of a closed-type commutated drum-armature winding entirely similar to that of a d-c machine, the brushes being short-circuited along an axis displaced by an angle α from the axis of the single-phase stator winding. The latter is disposed in slots around the inner periphery of a laminated ring similar to the stator frame of an induction motor.

     It is readily apparent that the single-phase alternating mmf supplied by the stator winding S of Fig. 15-19a can be resolved into two components, cophasal with respect to time, but displaced in space by 90º, so that one component is in line with the brush axis and the other is perpendicular thereto; or, what amounts to the same thing, the actual single stator winding may be regarded as equivalent to the two windings F and T of Fig. 15-19b, as has already been indicated in Chapter 5. Winding T then plays the part of the primary of a (series) transformer with the short-circuited armature winding acting as the secondary; and the reaction between the inductively supplied rotor current and the magnetic field due to F develops the torque. Since the current taken by the motor clearly varies with the load, and the flux due to winding F is proportional to the current (ignoring possible saturation), the motor is characterized by variable field flux and will therefore have the series characteristic of variable speed. One further fact evident from Fig.15-19b is that the magnetic field due to the armature mmf is largely neutralized by the mmf of winding T, which therefore serves as a compensating winding functioning by induction, instead of by conduction as in the series traction motor discussed in previous articles.

Further details

I have quoted only a small fraction of Langsdorf's discussion of the "repulsion motor." He has eight further articles on it, headed:—

15-11. Starting Conditions of the Repulsion Motor.
15-12. Phasor Diagram of Repulsion Motor, Running Conditions.
15-13. Analytical Relations in the Repulsion Motor.
15-14. The Circle Diagram and Performance Characteristics of the Repulsion Motor.
15-15. Commutation in Repulsion Motor.
15-16. The Compensated Repulsion Motor.
15-17. Phasor Diagram of the Compensated Repulsion Motor.
15-18. Doubly Fed Series and Repulsion Motors.

Langsdorf's articles on the so-called repulsion motor are by far the most thorough and useful I have found. His biographical notes are:—

Alexander S. Langsdorf, M.M.E., D.Sc.
Dean Emeritus, Schools of Engineering and Architecture, and Professor Emeritus of Electrical Engineering, Washington University
Fellow, American Institute of Electrical Engineers
Member, American Society of Mechanical Engineers

Orthodox repulsion motor: a "red herring"

I will have a lot more to say about genuine repulsion motors in future posts. Meanwhile, it is worth bearing in mind that the orthodox wrongly named repulsion motor is nothing more than a misleading "red herring," in comparison with those devices that do exploit genuine magnetic repulsion.