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).
Diagnostic procedure for testing an electric motor's magnetic circuit and mechanical friction.
| Identifier | ExFiles\Box 70\4\ scan0144 | |
| Date | 30th January 1925 guessed | |
| -2- Contd. an air gap, or of eccentricity of the armature. This latter has a double effect on the current :- Firstly, because the total flux may be reduced. Secondly, because the flux may be twisted round, so that the brushes are no longer in exact neutral position. Either of these will cause the current to be greater than normal. It will be seen that the light test should be quite sufficient to shew up a bad magnetic circuit, provided the mechanical friction is first reduced within bounds. Excessive current taken on the light test of the motor, due to mechanical friction in the gears, does not necessarily involve the motor being returned to the erectors, as friction of this kind is very often removed by running the motor on load. If, therefore, there is reason to believe that the excessive current is due to friction and not to bad magnetic circuit, it is legitimate to run this motor on the load test first and subsequently to carry out the light test. It may then be found that the light running is within the limit, so that the motor may be passed, if otherwise satisfactory. Note:- Before, between and after the light and load tests, the commutator and brushes should be carefully examined. The commutator should be found to be free from grease or varnish; this latter is difficult to detect when the motor is hot. The contact surface of the brushes should be carefully examined after the light test to see that there is sufficient area of contact, which we consider | ||