This study proposes a novel transverse differential protection for voltage sourced converter‐high‐voltage, direct current (VSC‐HVDC) to clear faults on DC‐line fast. The proposed scheme depends on the transient current of positive pole and negative pole at the same side. Transverse differential current can be used to distinguish DC and AC faults, novel criteria are built using the ratio of difference and sum current of bipolar. According to the variation characteristics of transient fault current, internal faults and external faults can be detected. The scheme can protect the whole transmission line without dead zone, simplify the algorithm and improve the speed of operation. A typical VSC‐HVDC model in PSCAD/EMTDC is built. The tolerance to grounding resistance of the scheme is researched in simulation. The results demonstrate the feasibility and reliability of the proposed scheme. The scheme can be used as supplementary criteria for primary protection or backup protection for VSC‐HVDC transmission lines.

The conventional transverse differential protection has some drawbacks such as, low sensitivity, long successive operation zone and being significantly influenced by operation mode when applied in high-voltage and asymmetric power systems. To overcome these drawbacks, an innovative integrated transverse differential protection scheme is proposed in this paper. This scheme includes three parts: faulty phase selection, faulty line selection, and tripping and reclosing strategy. The phase-selection criterion regards the two circuits as a whole and selects only the faulty phase. The criterion of line-selection distinguishes the faulty line with the faulty phase based on the transverse impedance ratio. Tripping and reclosing strategy decreases the number of operations of breakers and achieves Quasi-Three-Phase Operation as far as possible. Results of studies with PSCAD/EMTDC and on a dynamic physical model show that the proposed protection scheme can improve the accuracy of fault discrimination, decrease the successive operation zone and maintain more transmission power after the fault.

As the proportion of new energy generation continues to rise, power systems are confronted with novel challenges. Grid-forming converters, which possess voltage source characteristics and can support the grid, typically employ a VSG control strategy during normal operation to emulate the behavior of synchronous generators. This approach enhances frequency response and system stability in modern power systems. This review article systematically examines two typical fault control strategies for grid-forming converters: the switching strategy and the virtual impedance strategy. These different control strategies result in distinct fault response characteristics of the converter. Based on the analysis of fault control strategies for grid-forming converters, this study investigates the impact of the converter’s fault response characteristics on overcurrent protection, pilot protection, distance protection, and differential protection and investigates and prospects corresponding countermeasures. Finally, through simulation modeling, the fault response characteristics under different control strategies and their effects on protection are verified and analyzed. Focusing on grid-forming converters, this paper dissects the influence of their fault control strategies on relay protection, providing strong support for the wide application and promotion of grid-forming converters in new types of power systems.

In this paper, the necessity of the protective relay of the micro-grid is described as the anti-islanding protection and Low Voltage Ride Through (LVRT), and the fault characteristics of the renewable energy sources are analysed. The...

Due to the pseudo-bipolar structure of the flexible DC distribution network, the short-circuit current caused by a pole-to-ground fault is weak. The fault characteristics, particularly the steady-state fault characteristics, are not prominent. Therefore, pole-to-ground fault diagnosis and protection have become more challenging. This paper theoretically studies the short-circuit current characteristics of pole-to-ground fault in the flexible DC distribution network, derives the analytical expression of the short-circuit current, and analyzes the directional characteristics. Then, a novel pilot protection scheme based on fault direction comparison is proposed. This scheme compares the positive and negative half-wave integral values of the short-circuit current fault components to judge the fault direction. The fault directions on both sides of the feeder are obtained through the pilot protection channel, thereby distinguishing internal and external faults. The simulation results show that the proposed scheme can reliably identify the faulty feeder and has an excellent ability to perform with high transition resistance. Moreover, the scheme does not require sampling synchronization, which is easy to be applied in engineering.

During the no-load closing process, transformer will produce a magnetizing inrush current which will make the transformer relay malfunction and make adversely affect to the transformer equipment and power grid. Relative to a variety of external measures limiting the inrush current, the phase selection switch technology is more effective to reduce inrush current. The author analyzed inrush current by theory and dynamic simulation experiment. By controlling the closing angle to be less than 0° to 72° of the opening angle, inrush current is well suppressed.