A new sine-wave motor-generator set

A 3-machine sine-wave set, built to the author´s designs at the Indian Institute of Science, was completed in 1942. The alternators of this set embody new features which, the author believes, have not previously been employed in such sets. The set was made to be used primarily, in conjunction with other equipment, for testing standard and sub-standard wattmeters which are frequently sent to the Institute by supply authorities and consumers for testing, but it was also intended for several other purposes. It consists of a d.c. motor of 10 h.p. driving two alternators of about 10 kVA each, one of which supplies the voltage coils and the other the current coils of test instruments on the usual phantom-load principle. One of the new features consists of an electrical means of obtaining the required phase displacement between the current supply and the voltage supply for testing at various power factors, in place of the usual rocking-stator method. Another new feature is the use of the current alternator on (near) short-circuit instead of in the usual load condition. The design and performance of the alternators is discussed, and the test results show that the machines easily comply with accepted waveform conditions for instrument-testing purposes.