Electric ac machines temperature control and overheating protection

The paper reviews and analyzes basic methods of alternating current electric machines (EM) windings temperature control, such as thermometer methods, resistance and embedded thermocouples set out by GOST 11828-86. It also reviews indirect control methods based on the direct measurement of other physical quantities functionally related to the desired value, and computational control methods, based on mathematical modeling of the unit heating process using thermal equivalent circuits. The paper shows that the most appropriate EM winding temperature control method is the resistance method based on the principle of the conductor resistance - temperature dependence, which uses the EM winding as a thermal sensor. However, the EM windings thermal control problem has not been fully resolved and requires new principles for the construction of operational heating control systems. The paper suggests new method of the in-operation EM windings heating control, which does not require disconnecting from the network or disrupt the normal mode of operation. The method is based on the use of phase relationships between measured values as an additional informative parameter. The physical effects underlying this method are analyzed, the necessary operational implementation procedure is described. It is shown that the proposed temperature control method may serve as a convenient basis to build a thermal protection system, which can be in use both in the EM shutdown and in the control signaling modes. The paper also presents the results of the experimental test of the device based on the suggested method.