From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The poor performance of a motor during a brake test, with analysis of potential causes and comparison to an SC type machine.
| Identifier | WestWitteringFiles\H\November1921\ Scan18 | |
| Date | 10th February 1921 | |
| Contd. -3- EPCB/T12.11.21. characteristic of 1 volt drop per 75 amperes, and proceeded to make a brake test of the motor. The motor, however, did not perform any more successfully this time than previously as will be seen from my assistant's report of this test, which runs as follows :- "This motor behaved very badly on test. Tests were made, using a volt-ampere characteristic of 1 volt drop per 75 amps. It will be seen, however, that the motor could only be loaded up to a total weight of 15 lbs. i.e. a torque of 69 lb-ins. At this point the sparking at the brushes became serious, while with heavier loads, the sparking was such that in a few seconds running, the commutator was so blackened, that the volts, and consequently the speed and current, were continually fluctuating. "Also the whole motor including the bearings got very warm. "Generally it seems that this motor takes too large a current. In connection with this, the brushes appear too small, and one would think that commutation would be bad on account of armature reaction with such large currents. Also, as the number of armature slots is small, the current reversals in the conductors, when passing from one pole to another, would not occur so gradually, as in an armature with a larger number of slots, which again would cause flashing at the brushes. "This is somewhat borne out by the performance of the SC type machine, which is a higher resistance motor, taking less current, and having a larger number of slots, and which developed a torque of 93 lb-inches quite comfortably." Owing to the poor performance of the motor under test, we have not thought it worth while to plot the results. If a comparison be made for quantities for this motor and the SC motor upon which we have recently | ||