TABLE OF CONTENTS As has been described in Chapter 2, the limits to rating of electrical machines are generally set by the maximum permissible temperature that the insulation can withstand. Indeed the performance testing of machines, before they leave a manufacturer's works, is dominated by the measurement of winding or embedded temperatures and the need to achieve temperature rises within the appropriate standards. The measurement of temperature therefore has an important place in the monitoring of electrical machines and the following describes how this can be done using the measurement techniques described in Chapter 4.
There are three basic approaches to temperature monitoring.
To measure local temperatures at points in the machine using embedded temperature detectors.
To use a thermal image, fed with suitable variables, to monitor the temperature of what is perceived to be the hottest spot in the machine.
To measure distributed temperatures in the machine or the bulk temperatures of coolant fluids.
These approaches demonstrate the fundamental difficulty of thermal monitoring, which is resolving the conflict between point temperature measurements that are easy to make, but give only local information, and bulk temperature measurements that are more difficult and run the risk of overlooking local hot-spots.
The following three sections show how these approaches can be applied practically.
This can be done using thermocouples, resistance temperature detectors or embedded temperature detectors, whose characteristics are described in Chapter 4. To monitor the active part of the machine they are usually embedded in the stator winding...
