Experimental study of the transfer of overvoltage surges through distribution transformers

A high number of low voltage electrical appliances are damaged due to the presence of overvoltage surges that reach them coming from different points of the electric system. In order to clarify how the overvoltage surges coming from the distribution system pass through distribution transformers, an experimental study about overvoltage transference from transformer primary winding to secondary winding has been carried out on distribution and rural type transformers. The methodology consisted on applying dissimilar overvoltage surges to the primary winding, measuring and recording the wave that appears at the secondary coil, determining in this way its magnification, attenuation and change in waveform. As incident waveforms the normalized impulsive wave 1.2/50 µs was adopted. From the experimental results it can be concluded that the impulsive wave is transferred with considerable magnification (up to three times the value of the incident wave) regarding the winding rated voltage and showing a great change in waveform. On the other hand, it can be also concluded that the magnitude of the transferred impulsive wave is function of the transformer constructive characteristics.