THD improvement of phase voltages via injection of voltage in neutral conductor for three phase four wire distribution system

The effect of non-linear and unbalanced loads on the three phase four wire transformers are discussed in this paper. Unbalanced systems and harmonic load causes harmonic current to flow through the neutral wire of the distribution transformer and hence decreases the transformer utilization factor and efficiency of the system. Increase in the amount of neutral current causes over burden of the neutral wire and increase losses. Nowadays series active power filters are widely used to mitigate the effect of harmonics and in the case of three phase transformer, three separate active filters are required to reduce the total harmonic distortion of each conductor. In this research only one active power filter is installed in the return path of neutral wire of three phase four wire system. Simulations carried out show that only placing a single filter in neutral path, the THD of phase conductor voltages is much improved. Matlab/Simulink platform is chosen to perform simulation and the results are discussed for non linear and unbalanced loads.