GB888490A - Improvements relating to rotor temperature indicating arrangements - Google Patents

Abstract

888,490. Resistance measurement. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 10, 1959 [June 27, 1958], No. 20738/58. Class 37. A rotor temperature indicating apparatus for a dynamo-electric machine in which an ohmmeter calibrated in temperature has a current coil connected through shunt leads to a shunt resistor in series with the rotor and a voltage coil connected between one end of the current coil and the rotor terminal remote from the shunt resistor, comprises electrical resistance means so connected and proportioned relatively to the remaining components that the shunt leads carry currents of approximately the same magnitude to produce across such leads voltages whose algebraic sum in the closed circuit of the current coil and the shunt approximates to zero. An ohmmeter arrangement indicating the resistance and thus the operating temperature of the wound rotor R comprises a shunt S in series with the excitation thereof connected through shunt leads of resistance R2 and R3 in series with a swamp resistance R1 to the current coil C of a permanent magnet crosscoil meter whose voltage coil V (similar to the current coil) is connected from the junction of C and R2 through a swamp resistance R4 to the rotor terminal opposite to the shunt. An equalizing resistance R5 is connected across the voltage coil of such value that currents of approximately similar magnitudes flow in shunt leads R2, R3 in such directions that the algebraic sum of the P.D's. thereacross is approximately zero as regards the closed circuit including the current coil C, so that the current in the latter is independent of the resistances of the shunt leads; enabling a smaller value of shunt resistance to be employed and removing errors due to temperature variations of the shunt leads. Specification 615,597 is referred to.