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).
Continued page of test procedures for electric motors, focusing on load tests, magnetic circuits, and fault diagnosis.
| Identifier | ExFiles\Box 70\4\ scan0147 | |
| Date | 30th January 1925 guessed | |
| -5- Contd. On the load test, a bad magnetic circuit will reduce the speed by increasing the amperes and thus absorbing more volts on ohmic resistance, but on the light test, where the ohmic drop is comparatively small, the reverse is the case; a bad magnetic circuit would increase the speed because, owing to the smaller flux, the armature must revolve faster to generate the same back E.M.F. It is for this reason that on the light test we do not specify that the speed must exceed a certain amount, whereas on the load test we do. If the speed is not up to scratch on the load test, it may be due to the brush contact being bad, or in a lesser degree, to the electrical connections of the motor being bad and absorbing some portion of the voltage. This can be noticed by testing such connections by touch for unduly rapid heating. Note 1. A very good test for each brush consists in, on the load test, lifting off the companion brush opposite to itself, under which circumstances the brush under test has to carry the full current. If it does this without shewing signs of distress, which are indicated by jumping of the ammeter needle, it may be depended upon to be quite satisfactory when working in conjunction with its companion brush, provided this latter is equally good. Therefore, during the load test, each brush in rotation should be lifted off the commutator and the effect observed on the ammeter and opposite brush. Note 2. The joint constituting the series connection between the field and the armature should be watched for excessive heating, as this joint, unless made ultra-carefully, would appear to be rather a weak point in the electrical circuit and we have had cases of this heating up unduly. Contd. | ||