Additional Losses of Synchronous Machines

In the case of high-speed turbine generators, the cost reliable means of determining the losses under actual operating conditions is to measure the weight and temperature rise of the cooling medium and to estimate the small part of the losses which is dissipated from the frame to the surrounding medium. The temperature rise of the cooling medium can be obtained by means of temperature detectors located at the inlet and outlet sections of the generator. In order to obtain reliable values of the average temperature rise for the machine, it is necessary to have approximately uniform velocities at both inlet and outlet sections and to measure the temperature rise at a large number of incremental sections. The volume of cooling medium passing through the machine can be determined by (a) introducing a definite amount of heat energy into the cooling medium and measuring its temperature rise, or (b) measuring the mean velocity head at the outlet section of a properly designed stock. Loss tests were made on five 3600-rev. per. min. turbine generators when operated as synchronous condensers. In the case of these machines, the additional losses including the increase in core loss at full kv-a. and zero per cent power-factor load varied from 3 to 22 per cent of the total losses. This corresponds to approximately 0.14 to 1.0 per cent of the generator input. The additional losses as measured under sustained short-circuit conditions were from 5 to 10 per cent less than the corresponding values for full kv-a.