The use of electric power is a natural part of life. It is used everywhere for living, work and traveling, at any residence, commercial building , industry and so on , to supply the loads. The new technique devices , as loads , are used to achieve better performance , to be able to control and to transfer more power over the power system and to reduce the
power consumption of the loads . These new techniques consist of non-linear components that are used to control the load current. Non-linear components in power system distort the current waveform and can affect the voltage waveform. These distortions can create a variety of power quality problems. The voltage and the current distortion cause additional losses in power system components and in linear loads. Transformers are major components in power systems. Increase in harmonic distortion component of the transformer will result in additional heating losses, shorter insulation lifetime, higher temperature and insulation stress, reduced power factor, lower productivity, efficiency, capacity and lack of system
performance of the plant. The paper overviews and assessments the effects of real measured harmonic distortions on different low voltage level transformers supplying different types of nonlinear loads.