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).
Mathematical analysis of auto switch shunt coil heating.
| Identifier | ExFiles\Box 59\1\ Scan276 | |
| Date | 21th February 1928 | |
| X4008 21.2.28. AUTO SWITCH SHUNT COIL HEATING. Suppose switch operates at shunt coil current C amperes (fixed for a given setting). If the voltage is V and the resistance R ohms, V = CR.{Mr Cra???ster / Mr Chichester} The dissipation of the coil when the switch is just on the operating point is W₀ = C²R watts and is therefore proportional to R when R varies due to coil temperature variation. Now R = Rₐ + β(t - tₐ) where t is the coil temperature. tₐ " " ambient " R " " coil resistance. and Rₐ " " coil resistance at the ambient temperature. β being a coefficient of increase of resistance with temperature reckoned from the temperature tₐ. Further by Newton's law of cooling the coil watts W = γ(t - tₐ) γ being another coefficient. We have therefore R = Rₐ + (β/γ)W or W = (γ/β)R - (γ/β)Rₐ | ||