Harmonic measurements made on the upgraded New Zealand inter-island HVDC transmission system

This paper introduces the upgrade to the New Zealand inter-island HVDC transmission system. It then details the procedure of one of several tests conducted to measure harmonic levels created by the upgraded transmission system. Harmonic levels were measured using the CHART (Continuous Harmonic Analysis in Real-Time) harmonic monitoring instrumentation. The connection of CHART to the high voltage network and its configuration during the test is discussed. A sample of results gathered while monitoring are presented, including characteristic harmonics of the converter, and maximum voltage and current levels up to the 50th harmonic for each of the three AC phases. During the tests one of the two AC harmonic filters was switched out to observe its effect on harmonic levels. It was found that with both AC harmonic filters operating, most harmonic levels were lower than with only one filter operating. However one harmonic level, namely the 4th harmonic, was larger with both filters operating. The paper is concluded with a discussion of the results and of the difficulties encountered in measuring harmonics of very low level