Transformer hot spot temperature assessment terminated at transmission line through a cable under lightning impulses

This paper deals with the effect of distorted overvoltage and current on a transformer terminated at a transmission line through a cable that caused by striking of lightening on transmission line. Also the effect of harmonic current on transformer losses that cause overheating and aging of insulation is discussed. And then the hot spot and top oil temperature under the harmonic conditions using thermal model will be predicted. The thermal model is introduced by heat transfer principles including oil-to-air heat transfer and winding to oil heat transfer. And also the increase of harmonic current decline transformer life time. In addition, transient simulation is performed using EMTP software will show the longer cable the less amplitude of distorted operating conditions on the terminal of the transformer.