Patent GB-177603-A (GB)
Title: Improvements in, and apparatus for, testing dynamo-electrical machines
IPC: G01R31/34
Filed: 1920-12-30
Abstract: 177,603. Ytterberg, A., and Allmõnna Svenska Elektriska Aktiebolaget. Dec. 30, 1920. No Patent granted (Sealing fee not paid). Power meters; driving-arrangements and power supply for testing dynamo-electric machines.-In testing dynamo-electric machines in respect of heating at full load and of other characteristics, the machine is driven alternately as a motor and as a generator in sufficiently rapid succession to make it possible to store as kinetic energy the electrical energy corresponding to the desired current load whilst the machine is acting as a motor and to utilize this kinetic energy whilst the machine is acting as a generator, but not so rapidly that the changes involve considerable additional losses. The voltage impressed on the machine under test is caused to oscillate about a medium value with respect to magnitude, frequency, or phase, and may be composed of two component frequencies of which differ from each other by from 1 to 10 per second approximately. preferably by 5 per second. One of these components may correspond to the no-load voltage of the machine under test and the other to the voltage drop from no load to full load in all the machines involved in the test. In one method, the periodical variation in the impressed voltage is produced by periodical variation in the excitation of a driving-machine electrically connected to the machine under test, for instance, by shortcircuiting periodically a resistance in series with the field winding of the driving-machine or by superimposing a low-frequency alternating current on the excitation current. In another method, two series-connected machines, driven at different frequencies, are electrically connected to the machine or machines under test. If the machine under test be a continuous-current machine, a main driving-machine delivering continuous curent is series-connected with an auxiliary lowfrequency alternating-current machine. If the machine under test be an alternating-current machine, the main driving-machine 1, Fig. 3, is driven at a slightly lower speed than the auxiliary machine 2, and the machines 1, 2 are electrically connected to the machine 4 under test, through a transformer 3 if required. Instruments may be connected to the lines through current transformers 6 and voltage transformers 5. In the arrangement as shown for a three-phase system, the instruments comprise ammeters 7, 8, wattmeters 9, 10, a voltmeter 11, and a frequencymeter 12. The wattmeters are connected up in the usual two-wattmeter method for measuring power in three-phase systems and are combined with a switch 13 so that either their current coils or their pressure coils may be interchanged when reactive power is to be measured, each wattmeter then having its current coil in one line and its pressure coil between the other two lines. Two machines of approximately equal size may be simultaneously tested by connecting the main driving-machine 1, Fig. 9, to neutral points in the windings of the auxiliarv machine 2 driven at slightly higher frequency than the machine 1, the terminals of the machine 2 being connected to the two machines 41, 42 under test, one of the machines 41, 42 acting as generator whilst the other is acting as a motor and each machine acting periodically as a generator and as a motor. In all methods involving the series-connected driving-machines, the test may be started by running the machines in synchronism, forcing the auxiliary machine up to a higher speed, and then gradually exciting the auxiliary machine.