Harmonic currents have damaging effect on utility and end-user equipment. In this paper, a simple and feasible method to reduce zero-sequence current harmonics in neutral conductor of the three-phase four-wire distribution system is proposed. This approach is using a combination of a zero-passing transformer and a zero-blocking transformer. The zero-passing transformer has very low zero-sequence impedance while zero-blocking transformer has very high zero-sequence impedance. The passing transformer is shunt connected to the load while the blocking transformer is series connected to the source. This method able to suppress the zero-sequence harmonics from returning to supply. Harmonics pose a potential hazard to the electrical power distribution system and this approach should be able to suppress these harmonics to meet the following main objective, to reduce voltage harmonic levels to within limits set out in IEEE 519-1992 [20% THD of current and 5% THD of voltage with no individual harmonic above 3%. A study and analysis are carried out to obtain results to prove this harmonics filter approach is effective. Experimental results showed that the proposed method can reduce the neutral current and improve the power factor. However, the improvement is not significant and the THD of the line current is not reduced within the required IEEE-std519 harmonic standard.
A STUDY OF ZERO-PASSING AND ZERO-BLOCKING TRANSFORMER IN REDUCING NEUTRAL CURRENT IN 3-PHASE 4-WIRE POWER DISTRIBUTION SYSTEM_Nor Najihah Osman_E3_2007_875002751_NI