A study on zero-passing transformer in harmonics reduction

In this paper, a simple and practical approach to minimize the zero-sequence current harmonics in 3-phase 4-wire power distribution system is proposed. The zero-sequence current harmonic is minimized by using a very low zero-sequence impedance transformer. The very low zero-sequence impedance transformer is shunt connected to the load. Besides having very low zero-sequence impedance, this transformer also has very high both positive and negative sequence impedances. Thus, the zero-passing transformer has no effect on the positive and negative sequence harmonics. Because not all the harmonic can be reduced by zero-passing transformer, the LC filter is provided to cancel the entire harmonic. This LC filter is also shunt connected to the load. The dominant zero-sequence harmonic that is 3^rd harmonic current, which is generated by the load, will flow through the shunt load connected transformer and other harmonics current will flow through the LC filter. The practical excellency and validity of reduction technique are demonstrated experimentally.