Abstract
This paper presents a new fault detection algorithm based on the Fast Discrete Stockwell Transform. The algorithm can improve the functionality of existing distance protection and resolve shortcomings identified during the fault detection process in case of fault occurrence in systems with a high penetration of power electronics-based generators. Reported results of the operation of commercial distance relays of four different vendors show that all relays experience difficulties during ungrounded faults. An RTDS testbed is developed for extensive hardware in the loop testing, comprising electromagnetic transient models of Type-3 and Type-4 wind generators. The proposed algorithm successfully overcomes the identified problems for cases where commercial relays maloperate. The threshold parameters for the fault detection are set by using the energy content attributed to the Fast Discrete Stockwell Transform time–frequency domain signal. Other distance protection modules such as the determination of directionality, phase selection and the computation of the impedance, which are necessary for the protection selectivity, are developed based on currently available solutions applied in commercial relays. The new algorithm has been extensively tested using RTDS for various fault conditions and the obtained results are reported in the paper.
Highlights
In the future, a large number of coal and nuclear power plants will be decommissioned and replaced by renewable energy sources (RES)
In order to investigate the performance of the proposed algorithm, it was integrated into a full model of a distance relay developed in RTDS environment
This signif icantly improves the sensitivity and the speed of fault detection and overcomes the difficulties experienced by present commercial relays during the detection of ungrounded faults
Summary
A large number of coal and nuclear power plants will be decommissioned and replaced by renewable energy sources (RES). RESs such as photovoltaic systems, as well as Type-3 and Type-4 wind turbines (WTs) are commonly interconnected to the grid through partial or full-scale power electronics (PE) voltage source converters (VSC). This gives RES the capability of fast switching when necessary, in order to control their output power upon disturbances. The essentials of testing protection behaviour for power systems dominated by converter-based renewable generators (RWGs) are addressed in [3] and [4]. For this purpose, the FDST algorithm is incorporated together with other distance relay modules which are important to guaranteeing protection selectivity.
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