Improving the usage of temperature sensors for motor thermal protection

This paper presents different aspects of using temperature sensors as a part of the motor thermal model. Different types of sensors, mostly used on medium voltage machines, are presented. The most common solutions of building sensors into motor windings are described. The differences between induction and synchronous motors are discussed regarding the benefits of temperature sensor usage. It is considered how a sensor´s accuracy and time response can influence the efficiency of thermal motor protection. The basics of a typical temperature biasing algorithm are explained. A few modifications of the commonly used biasing methods are proposed. An option of comparing the calculated thermal capacity used with sensor readouts in the case of longer constant motor load conditions is discussed.