The economic importance of transferring maximum power via existing networks necessitates dynamic power control to keep transmission line temperatures within safe limits. Excessive conductor operating temperature leads to increased sag of the transmission line and may reduce conductor’s expected life. In this thesis, a passive wireless sensor based on a resonant radio frequency (RF) cavity is presented which can be used to measure the overhead transmission line temperature. This temperature sensor doesn’t need any power supply and can be easily clamped to the power line with an antenna attached. Changing temperature causes change of cavity dimensions and a shift in resonant frequency. Then, the resonant frequency of the cavity can be interrogated wirelessly. Such a system has the advantage of requiring no permanent physical connection between the sensor and the data acquisition system. In this thesis, also a theoretical basis of the sensor, design and simulation of the interrogator, optimizing coupling to the cavity sensor, calibration of the sensor, implementation and testing the temperature sensing system, sensor comparison with thermal models and so on is presented. The design presented here is a coaxial cavity resonator that exhibits electromagnetic resonance for wavelengths two times its cavity length and operates at a frequency of approximately 2.4 GHz, and can be interrogated from distance of greater than 4.5 meters. Experimental results have shown high linearity, low hysteresis, and a temperature resolution of better than 0.07 ?C on this sensor. Keywords: Passive sensor, RF resonant cavity, Power lines temperature measurement, Wireless sensors.
