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 long and short shunt windings and a discussion on cut-out defects and the Bleriot Compensated Cut-out.
| Identifier | ExFiles\Box 48\3\ Scan160 | |
| Date | 6th December 1920 | |
| Contd. -2- EFC {E. Fowler Clarke - Electrical Engineer} 1/T6.12.20. opposing winding by setting up ampere turns in opposition to those of the main shunt winding. Digressing for the moment to a consideration of the long and short shunt, quite apart from auxiliary winding, it would appear that the long shunt is the right connection for cutting in and holding on, as it enables the series turns to supplement the shunt winding for cutting in purposes, and also lowers the voltage on and current through the shunt winding during operation (due to volt drop in series coil). At the point of cutting out, however, when a reverse current is flowing from the battery, the long shunt has the slight/advantage that the voltage across the shunt coil is slightly greater than for the short shunt, and therefore slightly more reverse current in the series winding is required from the battery, to effect break. The claim of the makers with regard to the auxiliary winding is that this compensates for the change in the air gap. To quote the makers' own statement :- "Cut-outs of the usual types posses the inherent defect that whilst a pressure of, say, 13.5 volts is just sufficient to make it close the circuit, the pressure must fall very considerably below this value before the circuit is broken. This, is, of course, due to the change in the air gap. It is necessary therefore, to allow a certain reverse current to flow through the series winding, which reduces the attraction to such a value that the controlling spring can operate. This means that the cut-out always breaks the circuit when an appreciable current is passing, and the accumulator is being discharged". "The first of these points is the more serious as sparking occurs which tends to destroy the contacts. The Bleriot Compensated Cut-out overcomes these defects entirely, and possesses other valuable advantages". Contd. | ||