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Online detuned element identification for a filter based on the harmonic current change rate

ABSTRACT Online detuning state detection and the subsequent detuned element identification of a passive filter bank is of great concern in regard to achieving condition-based maintenance of an HVDC transmission system. In this paper, a novel method that can rapidly detect the online detuning state of filter banks with arbitrary structures of an HVDC system and accurately identify the detuning element is proposed. The method is based on the calculated amplitude change rates (ACRs) of several deliberately selected harmonic components of the measured real-time current in each branch of the filter. The principle and the implementation of the proposed method are presented, and the relationship between the ACR of the harmonic current and the detuning degree of an individual element is deduced theoretically. Based on the above works, the criteria for identifying the detuning state of the filter bank, the detuned element in the series and parallel part of the filter, and the detuning degree of the element are given. Diverse simulation results, such as applications on a single- and a double-tuned DC filter bank, sensitivity analysis and performance comparison, are provided to show the correctness and the effectiveness of the proposed method.