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 the principles for redesigning a coil for optimal magnetic field energy, efficiency, and high-speed operation.
| Identifier | ExFiles\Box 52\3\ Scan296 | |
| Date | 11th December 1917 | |
| Contd. -8- EFC {E. Fowler Clarke - Electrical Engineer} 2/T11.12.17. not an unmixed advantage, for it means doubling the voltage to double the output of the same coil. If we redesign our coil to double its output, our basis would seem to be that we desire to produce a magnetic field of a certain fixed energy value ½ L.C.² in the least possible time and with the best efficiency. We may now consider L C² fixed, but that we may vary L and C dependently with this condition. Supposing for the moment that E, R, and therefore Co are fixed, it may be shown that the least time to establish a magnetic field of this amount of energy, occurs when C is a definite fraction of Co viz., .716 and L has a corresponding value. The efficiency has also a corresponding value namely .473). If now, retaining this value (or any other fixed value) of the ratio C/Co, we allow C and Co to vary by varying E and R, and L to vary also in such a manner that L C² is a constant, it may be shown that the time required to establish the given amount of magnetic field energy is smaller the greater the values of C and Co, and the smaller the value of L. Thus a coil for high speed operation should have a low value of L and a high value of Co. The low value of L implies also a low value of the primary coil resistance R1 in proportion, because we must keep R1 C², which is proportional to the heating effect in the coil, down to a certain figure. The operating voltage R1Co is therefore reduced and we may take advantage of this fact. | ||