GB869243A - Improvements in and relating to synchronous dynamo-electric machines particularly for prime mover starting - Google Patents

Abstract

869,243. Control of A.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Sept. 7, 1959 [Sept. 25, 1958], No. 30713/58. Class 38 (3). [Also in Group XXXV] A synchronous machine MM is coupled to an auxiliary machine AM operating either as a starter motor or an exciter for the synchronous machine. As shown, the stator windings ST1a and ST2a are arranged in parallel, and current transformers CT have their secondary windings CTS coupled to primary windings PW connected to supply lines SL through voltage regulator VR of the saturable reactor type. The output from the rotor windings RO2a of the auxiliary machine is connected through rectifiers RFa to the rotor windings RO1a of the synchronous machine. When the voltage regulator VR disconnects the primary windings PW from the supply lines, the machine AM operates as an induction motor, the stator windings of the two machines being connected virtually in series. When the machine MM reaches synchronous speed, the voltage regulator applies to the windings PW a potential dependent upon the supply voltage and the phase connections of the windings ST2a are reversed, whereby the machine AM now operates as a frequency changer and provides excitation for the main machine under the control of the voltage regulator. The auxiliary machine may have its pole number increased when changing from motor operation to operation as a frequency changer. During motoring operation, the rotor windings RO2a may be associated with a two-pole field and carry only circulating current, no current being diverted to an external circuit. When operating with a four-pole field, there is substantially no circulating current, and current generated in the windings is delivered to the field of the main machine. The auxiliary machine may have a four-pole stator winding associated with a short-circuiting switch and connected in series with the stator winding of the synchronous machine. An eight-pole stator winding of the auxiliary machine may then be connected to the supply through switches interlocked with the shortcircuiting switch, Fig. 5 (not shown). Specifications 841,585 and 842,916 are referred to.