Systems of Single-Phase Regeneration for Use with Series Type Commutator Motors

The alternating-current series motor may be adapted to regeneration in a number of important respects more readily than a similar direct-current series motor on account of the following features: (1) The a-c. motor always employs a cross-field winding which prevents armature distortion. (2) A relatively low impressed commutator voltage is used reducing the danger from flashing. (3) With the a-c. system a transformer can be used to obtain desired variation in motor voltage. The advantages of this feature are outlined at length with reference to its effect on regeneration. The several schemes of regenerative connections are divided into four classes as follows: (1) Series excitation; (2) self-excitation, or cross excitation; (3) shunt excitation; (4) separate excitation. The first two connections have not been commercially used. A number of fundamental assumptions as to the theory of the single-phase motor are given as a basis for vector diagrams, which are used to analyze the conditions for both motoring and regeneration for the four types of connections. A detailed presentation of the conditions which obtain with these connections is then given by the author. When using the first connection for regeneration it is necessary with series excitation to reverse the main field with reference to the motoring conditions. With the alternating-current series motor a sudden decrease in the line voltage will not increase the regenerated current as in the case of direct current, but will tend to decrease it.