A Passive Hottest Spot Detector For Transformers

The hottest spot conductor temperature in a transformer winding is one of the principal factors of influence in determining the life of a transformer. Previously, this temperature could not be measured directly because of the hazard of placing a temperature detector imbedded within windings which are at relatively high voltage potentials. Simulated devices have been used which include emperical allowances. A hottest spot detector which may be imbedded safely within the windings giving an accurate temperature indication has been developed and model tested. The device is compact in size and completely passive inside the transformer tank. Using acoustic principles the sensor resonates at discrete frequencies and is temperature dependent. A relationship is shown to exist between Young's Modulus, Y, of the sensor and temperature which causes the resonant frequency shift. The sensor design and acoustic waveguide link are shown in detail. Experimental data is presented to substantiate the hottest spot detector performance and methods of winding implantation are described.