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).
Analysis of a motor's performance, comparing test results with initial calculations for torque and winding.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan134 | |
| Date | 22th June 1927 | |
| -2- Contd. The performance of this motor on static torque and brake test did not come quite up to that represented by our calculations dated 22.6.27 based upon the new 16 : 1 ratio, sent under cover of our EFC5/T22.6.27, which calculations were based on a non-taper armature of 3.100" diameter. Actually the armature tapers from 3.100" to 2.900". It appears difficult in these small motors, unless there is a good margin or freedom in electrical and magnetic design, as there was in the case of the 20 H.P. motor, to realise the permeance of the magnetic circuit and the conductance of the electric circuit that might be anticipated; or in other words the calculation of the ampere turns of the field is only an estimate at the best. In accordance with the figures quoted in the calculations, we hoped to get a static torque or torque on the conductors themselves of 89 lb-inches at 180 amperes of current, and further we hoped to do this with 3½ or at most 4½ turns of main winding per pole. Actually we have found that to accomplish this approximately requires 6½ turns per pole, when we get actually on test a conductor torque of 84 lb-inches at .180 amperes. The electrical resistance of such a main field winding of 6½ turns per pole, is in view of the necessity of providing a teazer winding, only as low as .016 ohm cold, whereas our calculation figures demanded only .008 ohm. Correspondingly the motor speed at any given torque is less than anticipated. We can get the resistance down to this value by using 4½ turns per pole but since the | ||