Due to complex disturbance environment, partial discharge (PD) monitor signal denoising is a necessary step to judge the state of equipment insulation. In the denoising process, it is difficult to suppress the white noise due to its wide frequency-domain distribution. To overcome these difficulties, most denoising algorithms need to artificially adjust some threshold parameters or select the number of decomposition layers according to the measured PD signals, which leads to the confusion of uncertainty, and the denoising performance depends on the parameter setting experience. Therefore, the denoising effect cannot be guaranteed in general. This article proposes a method without human intervention in choosing the threshold parameters or the decomposition layer numbers. First, the decomposition layers are directly determined from the spectral kurtogram of PD signal to obtain the reference signal. Second, the reference signal is denoised by 3σ threshold. At the start point obtained from the denoised signal and the end point obtained from the reference signal envelope, the reference signal is segmented in the time domain to obtain the final denoising PD signal. The denoising results of both the simulated and field-measured PD signals show that the proposed method can effectively remove the white noise and recover PD signal more accurately.

It is still a significant challenge to accurately locate faults of grounding electrode lines in high voltage direct current (HVDC) transmission systems, especially high resistance faults and remote faults. In this paper, a novel fault location approach based on characteristic-harmonic measured impedance (CHMI) is proposed. This method works well under high resistance faults and remote faults. Considering that there are abundant and steady characteristic harmonics in electrical signals of grounding electrode lines, the CHMI is defined first according to the equivalent circuit of the grounding electrode system. Then, the CHMIs of the two grounding electrode lines under faults are analytically derived. On the basis of that, the fault branch is identified by the amplitude ratio of the two CHMIs. Furthermore, since both of the CHMIs of the two lines are relevant to fault distance and fault resistance, the precise fault distance is obtained by solving two fault location functions simultaneously and eliminating fault resistance. The proposed algorithm is finally validated through numerous simulations covering various fault scenarios carried out in PSCAD/EMTDC.

The protection of high voltage direct current (HVDC) transmission line is the key to development of the HVDC transmission technology. To deal with the problem that the traditional traveling wave protection (TWP) has low sensitivity under high resistance faults, an improved TWP scheme based on the compensation of the line-mode component of fault voltage (LMCFV) is proposed. The expressions of the LMCFV of HVDC system at different fault locations are derived. Conclusions can be drawn that the LMCFV and fault resistance are linear when the DC line fault occurs, whereas the linear state will be broken for the external fault. Based on this, the LMCFV for the metal fault occurring at the DC line midpoint is used as the reference value to compensate for the faults in other cases of the HVDC systems. The protection scheme constructed based on the compensatory LMCFV and compensation coefficient can accurately identify fault of the DC line. Finally, a ${\pm }$ 800 kV model of HVDC systems is built in PSCAD to verify the protection performance. The effect of fault resistance can be eliminated by compensatory LMCFV, and the DC line fault can be quickly and reliably identified by the simulation results.

High frequency current injection-based protection is widely used for fault detection of grounding electrode line in high-voltage direct current (HVDC) system. Since the grounding electrode line is several times longer than the wavelength of the injected current, the relationship between the measured impedance and fault distance is very complex. Due to the complex impedance characteristic, the current injection-based protection has dead zone under some circumstances. To eliminate the protection dead zone, an improved approach to high frequency current injection-based protection was proposed. First, the characteristics of the high frequency impedance of the grounding electrode line under different fault conditions were investigated. Analysis results showed that when the line length was close to the integer multiple of the half wavelength of the injected current, the measured impedance of the grounding electrode line may be the same as normal operation impedance. Thus the current injection-based protection will be unable to recognize the fault. Second, a two-layer optimum method was proposed to select the frequency of the injected signal. With the new frequency, the current injection-based protection was able to eliminate the dead zone of the traditional protection. Finally, a ±800 kV HVDC simulation model was constructed, and the simulation results verified the accuracy of our conclusions and the effectiveness of our proposed protection method.

Active grounding device (AGD) is an effective device to eliminate grounding arcs and prevent disasters caused by ground faults in distribution networks. However, due to the uncertainty of the ground fault resistance, the traditional arc suppression control cannot guarantee the suppression effect and the control stability simultaneously under the fixed control parameters. In this article, an arc suppression control method based on adaptive parameters is proposed. According to the dual-loop control model of the AGD connected to the fault distribution network, the relationship between the model input and the fault voltage is derived. Then in two extreme cases of the ground fault resistance, the suppression effect and the system stability are analyzed using the amplitude-frequency curve and the root locus, respectively. Further, a control method is proposed to make control parameters self-adaptive through the feedback information of the residual fault voltage. Finally, the effectiveness of the proposed control method is verified by the simulation model of MATLAB/Simulink and the low-voltage experiment of the prototype, which can realize arc suppression with high, low or dynamic resistance ground 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.