Impact of power system harmonics on insulation failure of distribution transformer and its remedial measures

The ageing of insulation denotes physical and chemical changes, which takes place as a result of electrical stresses in the power system network. In the modern days, a large use of nonlinear devices has resulted into increased distortion in load voltages. The current drawn by all such devices contains harmonics. The losses as well as insulation are more in the equipment at harmonic frequencies than the fundamental frequency. The thermal circuit capability at the fundamental frequency is inadequate to dissipate increased losses due to harmonic current. Hence excessive current drawn during steady state and dynamic power quality problems resulting into the higher temperature rise. The increased use of the non-linear devices in today´s network is responsible for faster degradation of insulating material. The transformer transfers electrical energy from one point circuit to another. The additional heating experienced by a transformer depends on the harmonic content of the load current & the design principals of the transformer. In this paper, an attempt has been made to discuss the procedure for loss calculations and analysis of impact of the temperature rise on conventional oil immersed and derated transformer under the non-linear load conditions. Some remedial measures are also suggested to reduce the impact of harmonics on insulation failure.