Figure 2 shows a schematic of the test system. The test
equipment consists of a DC load machine coupled to the
test motor by a torque transducer mounted in a Carden
shaft. There are no additional bearings between the torque
transducer and the test motor. Armature current control
using a Ward Leonard system ensures smooth torque from
the DC machine even at light load. The AC supply to the
test motor is provided by an AC generator, which is driven
by an inverter-fed, synchronous motor. This configuration
gives precise and constant supply frequency. The automated
voltage regulator of the generator gives voltage control
from 0 right through to 130% of nominal rated value.
Supply imbalance and distortion are negligible with a
balanced load. Coupled to the same shaft as the generator
and synchronous motor is a DC machine which forms part
of the Ward Leonard system and which reclaims energy
from the test motor.