Temperature measurement of high-density winding coils of electromagnets

In this study, the temperature of high-density winding coils of electromagnets is measured without using any temperature measurement probe. In fact, the probe cannot get access to the interior of the coil. Infrared radiometry can measure only the coil surface temperature which can be very different from the interior temperature. In the present measurement technique, the copper winding wire itself is used as the temperature-sensitive element. The current against voltage (I-V) of the coil is first measured. The electrical resistance of the coil is then obtained and plotted against dissipation power. Using the thermal coefficient of the electrical conductivity of copper at ambient temperature (20°C), the coil temperature is deduced and plotted against dissipation power. The resulting temperature is the temperature along the wire averaged over the entire wire length. This is the average interior temperature rather than surface temperature. The case temperature is measured by a precision thermometer. The difference between coil temperature and case temperature is calculated and divided by dissipation power to attain the thermal resistance from the coil to the case. For the electromagnet studied, the thermal resistance is 1.1°C/W. Electromagnets are components that are used in numerous electrical machines and electronic products. Coil temperature measurement is of critical importance because the insulating coating of the winding wire has finite temperature ratings beyond which the coating may deteriorate and get damaged. By using the pulsed mode, the technique presented here can be implemented to measure the coil temperature even while the electromagnets are in operating conditions. It should be valuable to the electricity and motor industries.