By B. J. Chalmers (Eds.)
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The procedure for the synchronizing of a synchronous motor which is run up by means of a pony motor is similar to that for synchronizing a generator to the 34 m a i n s . c. excitation when the rotor approaches synchronous speed. Therefore the asynchronous torque must be capable of accelerating the rotor to a speed at which the maximum excitation current is capable of pulling the rotor into synchronism. It is convenient to consider here a further function served by the starting windings. When a synchronous motor is subjected to any sudden change such as to cause it to seek to develop a new value of load angle, it is prevented from responding to its natural tendency to oscillate about the new value by the damping action of the asynchronous torque developed by the starting windings.
This can be achieved by the shift of brush axis on the commutator, but if the shift is correct on one side of synchronous speed it is incorrect on the other. Therefore the phase shift must be achieved in the control circuit. One method is to use a separate auxiliary transformer. A better method is to incorporate the phase shift in the voltage regulator itself. In one type of regulator, the double induction regulator, this can be done in such a way that the phase shift is zero at the extremes of the voltage - and therefore speed - range and a maximum in the middle of the range.
C H R I S T O F I D E S , N . 'Origins of load losses in induction motors with cast aluminium rotors', Proc. Inst. Elec. Engrs, 112, 2317 (1965) 16. A L G E R (1965) op. cit. 17. A L G E R (1965) op. cit. 18. SAY (1983) o p . cit. 19. C H R I S T O F I D E S (1965) op. cit. Characteristics 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 61 M O R G A N , T . , B R O W N , w . Ε . and S C H U M E R , A .