Direct Measurement of Generator Winding Temperature Using a Miniature Transmitter

The direct measurement of stator winding copper temperatures in large electric machines is made possible with a miniature tunnel diode oscillator, mounted directly on the current-carrying conductor. A temperature-sensitive capacitor in the oscillator's resonant circuit causes the radiated signal frequency to change as copper temperature changes. This signal, radiated through the thickness of the winding ground insulation, reaches an antenna external to the ground insulation. Then this signal is compared with one from a calibrated external oscillator, using a standard AM (amplitude modulated) radio circuit which will indicate changes in transmitted frequency. Calibration curves of frequency vs. temperature will reveal the copper temperature at the transmitter.