GB251994A - Improvements in and relating to differential frequency relays - Google Patents

Abstract

251,994. British Thomson-Houston Co., Ltd., (Assignees of McDonald, G. R.). May 6, 1925, [Convention date]. Systems depending on two or more machines. -An electric control device comprising a pair of shading ring motors 23. 24 is applied to a system comprising a synchronous motor 1 supplied from lines 2 and driving a generator 4 supplying a distribution circuit 5, it being desirable to supply the field of the motor 1 from the generator 5 by the closure of switch 6 when the generator speed bears a certain relation to the frequency of the lines 2. The motor 24 is supplied from the lines 2 through a transformer 34, and the motor 23 from slip rings 38 on the generator. Assuming the line frequency is constant and the generator to be increasing in speed the torques exerted by the stators 29. 30 upon the motor 24 will remain constant, whereas the torque of the stator 27 upon the motor 23 will increase relatively to that of the stator 28 owing to a condenser 39 being included in the circuit of the winding of the stator 27. Thus the motor will turn anticlockwise and close contact 14 on to fixed contacts 13, 15. This results in the energization of switch coil 16, to close switches 10<1>, 17, the former causing closure of the switch 6 and the latter completing a " hold on " circuit for the coil 16. Should the speed of the generator fall, the motors 23. 24 turn clockwise, and close contact 14 on to fixed contacts 18, 19 thereby shorting switch coil 16 and opening switches 10<1>, 17, 6. A condenser 35 in circuit with the winding of stator 29 causes a similar action should the speed of the generator 4 be constant and the frequency of the lines 2 be changing.