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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 failure analysis of two 20 HP dynamos from chassis 50 S.1 and GHK.78.

Identifier  ExFiles\Box 57\2\  Scan104
Date  2nd September 1927
  
To EY. from EFC.
c. Mr. Brock
X5783do
EFC L/T2.9.27.

20 HP. DYNAMOS.

No.123 Ex Chassis 50 S.1.

This is a 29 segment machine and a very early one. The failure has been due to the usual familiar circumstances connected with these earlier machines, e.g. high micas, too much retarded control brush, etc, which has resulted in more rapid wear of the brushes than would otherwise have been the case, with the consequence that the negative brush has worn right down and set up very bad sparking and consequent heating.

We return the machine to EY.

No.1025. Ex Chassis GHK.78.

This is also a 29 segment machine, but a later one. The circumstances in this case are not quite so straight forward or bad. The control brush angle is 119° as against 128°. This would make the output larger. The main brushes were found to be a bit sluggish in their holders, but the micas appear to be alright.

It would appear that this machine must have been dis-assembled away from the Works as the bakelite oil thrower on the front of the commutator is now jammed against the ends of the screws projecting through the bearing retaining ring. One would have thought that this could not have been possible.

We note from Mr. Brock's statement concerning this machine that this was overhauled, and he thinks the poles were modified last November; this would appear to suggest that in the case of this machine it is a question of customer's interference.

In regard to 20 HP. dynamo failures generally, may an arrangement now be made that we do not receive any more of these of the 29 commutator segment type, as it seems unlikely that there is anything further to be gained by our examining such machines. In case of failure of 57 commutator segment machines, the case is different, and we should be anxious to see failures of this type. In this case, a failure must mean some special circumstances, which we should have an opportunity of
  
  


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