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).
Investigation report into two faulty coils, nos. 4405 and T145X, from the repair department.
| Identifier | ExFiles\Box 70\3\ scan0128 | |
| Date | 4th February 1928 | |
| X87832 To BY.{R.W. Bailey - Chief Engineer} from EFC c. Mr. Brock. c. BY/RD. EFC2/T4.2.28. COILS NOS. 4405 and T145X, EX REPAIR DEPT. X Y710 We have duly tested and afterwards unwound these coils for examination. Both coils showed weakness of secondary spark on normal running. They were then tested for secondary continuity and winding quantities and all these were found to be O.K. on both coils. It was clear, therefore, that the weakness must be due to faulty secondary insulation. The coils were then unwound for investigation. Coil No. 4405, when unwound showed that the oil paper on the secondary winding was in some places still wet with varnish, otherwise the coil windings were O.K. [crossed out: though] They were not charred. It would appear that this coil was not properly baked or dried out enough in the first instance. Coil No. T145X, when unwound showed [strikethrough] signs of overheating, evidenced by a certain amount of charring, the insulation of primary and secondary being somewhat charred, this being more confined to the vicinity of the primary winding and on the primary winding itself. It would appear that this is sufficient explanation of the weakness, as in this case the remainder of the secondary insulation appeared perfectly dry. We know from experience that it is highly essential for the windings of the coil to be dry, not merely in the sense of the absence of water vapour, but also in the sense of the absence of spirit or oiliness, as the case may be. There is always a definite leak through wet varnish between conductors at different potential. It should be noted that both coils are of the coarser 22 SWG. gauge primary. In the case of the charred coil, we think it probable that this must have been accidentally left on circuit, as it is nearly inconceivable that the watts dissipated in the coarser gauge coil primary with the intermittent current in normal running would be sufficient to produce this effect. We tried the experiment of treating these coils with paraffin wax at suitable temperature. This, however, did not produce the effect of strengthening the coil. The reason for this was clear from unwinding, namely that the wax did not percolate into the innermost regions of the winding where the weakness was greatest. Particularly on the coil which was wet with varnish, the wax did not find its way inside at all. Contd. | ||