Patent GB-1227134-A (GB)
IPC: G01R31/34
Filed: 1967-04-19
Abstract: 1,227,134. Testing dynamo electric machines. D.G.O. MORRIS. April 17, 1968 [April 19, 1967], No.17890/67. Heading G1U. The power loss in an induction machine is tested, using a power source of lower rating than the machine, by a back to back method in which the machine is mechanically coupled with a similar induction machine or with a synchronous machine, the two machines being run as motor and generator at different speeds to produce an economical loading of the machine under test, the power loss in the system being measured. To compensate the measured power loss for the power losses in the mechanical coupling, the rotors of the machines are caused to rotate in the same sense with their torques opposed and with the total torque on the rotor system adjusted to zero. Two main machines 35, 36 under joint test have their respective shafts 1, 2 connected by an energisable coupling 37. Electrical power is supplied at 41. Wattmeters 38 measure losses and wattmeters 39 measure the full power circulation, so that the joint power input to the machines and the power in either one machine may be determined. A dynamometer 34 may be provided for applying torque bias to the rotating shaft 1, and this dynomometer and the coupling 37 have independent supplies which are adjusted through control arrangements to enable the total torque on the mechanically coupled rotor system to be adjusted to zero. Power to make up for the losses may be provided mechanically at either the coupling 37 or the dynamometer 34, if present, or electrically through the meters 38. If the make up is provided entirely mechanically, the dynamometer 34 and coupling 37 are adjusted such that the meters 38 read zero at any desired loading, the loss being the sum of powers provided by the dynamometer and coupling. The loss may alternatively be supplied entirely electrically by reversing the dynamometer torque and arranging that the power withdrawn by the dynamometer equals the power injected by the coupling 37. In one form of coupling, as shown in Fig.2, a supplementary bias torque is not required. The two induction motor shafts are coupled through a coaxial gear box 3, tubular yoke 4, stub shaft 5, and boss 6 containing a torque transducer for measuring the differential torque. A motor 7 drives the input shaft of the gear box to cause relative rotation of the output shaft to produce torque balance. Stroboscopic marks on the flanges 8, 9 enable the relative speeds to be determined. The supplies to the motor 7 and torque transducer are fed via brushes within a housing 10. Any significant friction due to these may be balanced by a torque applied at an arm 12. This can be measured and if significant used to correct the main measurement. An alternative arrangement Fig.3 (not shown) incorporates a close ratio gear box with a torque nulling motor bolted to its housing and exerting torque on the shaft 1 from the induction motor. In order to carry out tests under varying load conditions Fig.4 (not shown) a close ratio double input epicyclic gear box may be used incorporating two sun wheels of slightly different size coupled to the respective input shafts and coupled by pinions on pairs of layshafts. A second input representing the loading conditions is applied from an auxiliary motor (22) which rotates the carriage (18) carrying the layshafts to give them a planetary motion. Torque balance is then achieved by adjusting a further motor (25) which applies a torque between the floating housing (21) and a main shaft, the torque being measured by auxiliary transducers as before. The coupling arrangements must be supported without imposing rotational constraint on the system and a suitable platform hung by a parallelogram linkage from a spring suspension pivot is used Fig.5 (not shown).