As the core connecting equipment between the generator and the power system, generator circuit breaker is commonly installed in various power stations. Its main function is to quickly cut off the fault current in case of a fault to ensure system safety. Taking the fault of the operating mechanism during the closing of a generator circuit breaker as an example, this article clarifies the cause of the operating mechanism fault through disassembly inspection, trace analysis, and design data inspection of the faulty part, and proposes relevant preventive measures. The analysis results have important reference significance for the optimization design and operation maintenance of the operating mechanism of the generator circuit breaker.

High impedance fault (HIF) is difficult to detect because of the low fault current amplitude and they can be easily confused with switching events. Existing HIF detection methods mainly rely on fixed time-window data. However, a fixed decision time often fails to balance the accuracy and speed of HIF detection. Thus, a sequence-adaptive HIF detection model is proposed in this paper. Firstly, zero-sequence current data of the faulty feeder are processed into variable-length training set. Then, a gated recurrent unit (GRU) model is trained based on variable-length data and cost-sensitive coefficient method to construct biased models. Two GRU models with opposite propensities are combined into an evaluation model. The test results on the PSCAD/EMTDC simulation platform show that the detection accuracy rate of this proposed model can reach 99.13%, and the detection speed is improved by at least 37.52% compared to the fixed time-window method. Delayed decision-making improves the accuracy of HIF detection and reduces the risk of harm.

DC equipment is very important in power supply system of subway, which directly affects the driving and metro operation. When the DC bus encounters a shell collision fault, it can quickly cut off fault current by setting frame protection to ensure the safety of the person and the equipment. In this paper, by introducing the principle and function of frame protection, optimization solutions are explored to reduce the probability of malfunction through case studies.

The fault current limiter can effectively limit the fault current level in a very short period of time, so as to prevent excessive short-circuit current from causing potential harm to the safe and stable operation of the power system and electrical equipment. It has become a key equipment to suppress short-circuit current in the power system. In this paper, the working principle of the fault current limiter is summarized firstly. Then, the influence of the installation position of the fault current limiter on the busbar differential protection under different main wiring modes is discussed in depth. The research results show that the action of the fault current limiter may reduce the sensitivity of the busbar differential element. Through the scientific and reasonable arrangement of fault current limiter and the reasonable setting of differential restraint coefficient, it can effectively prevent the rejection of busbar differential protection and ensure the safe and stable operation of power system.

Under pressure, the magnetic field outside the ferromagnetic cavity is more complex under the influence of the background magnetic field, which reduces the accuracy of magnetic detection. Therefore, a comprehensive study of the influence of background magnetic fields on spatial magnetic fields is of great significance. In this paper, a magneto-mechanical coupling model for an oxygen tank is developed based on the improved Jiles-Atherton theory, and the composition of the spatial magnetic field is classified. The influence of the background magnetic field on each component of the spatial magnetic field is simulated and calculated. By establishing the relationship between the induced magnetic field and the background magnetic field, and analyzing the influence of the background magnetic field on the magneto-mechanical coupling effect under specified pressure, references are provided for the magnetic detection.

DC optical current transformer (OCT) is an important equipment in high voltage direct current (HVDC) transmission project. Its safety and stability is of great significance to the power grid. In this paper, the causes of a DC optical current transformer fault at a converter station are analyzed and the possible location of the fault is investigated. Finally, it is determined that the change in the characteristic parameters of the fault is caused by the cracks produced after the long term deterioration of the optical fiber melting point. This work is of certain reference value for fault analysis of the OCT in engineering.

Based on the fault characteristics following the disconnection of the secondary circuit of a potential transformer (PT), a detection method for PT secondary break utilizing the principle of sequence voltage ratio is proposed. This method primarily calculates the ratio of the positive sequence voltage to the negative sequence voltage from the PT’s secondary voltage data to determine the occurrence of a PT break. Simulation results demonstrate that this criterion can accurately assess whether an asymmetric disconnection has occurred in the PT secondary circuit, particularly advantageous when the PT secondary circuit is concurrently connected to both delta and star loads.

The aging phenomenon of transmission lines poses a serious threat to its safety and stable operation. Condition based maintenance is gradually replacing the traditional periodic maintenance as an important means of transmission line maintenance due to its strong targeting, good economy, excellent maintenance effect and other characteristics. As an indispensable basic step in the process of condition based maintenance, state assessment is based on the analysis of equipment condition index data, which can accurately reflect the health status of the equipment, and discover potential faults in a timely manner. To this end, this paper proposes a transmission line condition based maintenance method. The aging fault prediction model is built through the assessment of the transmission line components of the health index. The probability of aging faults and their consequences are quantified to achieve the probability of aging faults year by year prediction. The risk of aging phenomenon from the level of economic loss is quantitative analyzed. The condition management and risk assessment are combined to provide decision support for managers to formulate overhaul, technical improvement and end-of-life replacement programs for relevant components of transmission lines.

Considering the problem that the active power output from storage modules cannot be reasonably distributed in a multi-storage AC microgrid, this paper proposes an improved droop control strategy based on the state of charge of the energy storage module, on the basis of stabilizing the frequency of the microgrid. Firstly, by constructing a power-exponential function model of the energy storage state of charge and droop coefficient, this control strategy enables each energy storage module to adaptively adjust the output active power according to its own state of charge, which ultimately achieves the state of charge equilibrium. Secondly, small signal analysis is used to analyze the stability of the strategy. Finally, the effectiveness of the proposed strategy is verified by Matlab/Simulink simulations and semi-physical experiments.

Three-phase grid-connected inverters are usually digitally controlled, and due to the negative damping effect brought about by the digital control delay, grid-connected inverters are prone to interact with the grid impedance (capacitive reactance) to produce high-frequency harmonic resonance when they are connected to the grid, which seriously affects the safe and stable operation of the power system. For the negative damping problem brought about by the controller delay, the low-frequency coupling effect of the inverter is ignored, and a high-frequency impedance model is established to reveal the high-frequency resonance mechanism, and the results show that the negative damping brought about by the delay exists a high-frequency resonance risk in the resonance peak interacting with the grid impedance. To improve the high-frequency resonance stability, based on the idea of passive design of the control loop, an approximate high-frequency passive composite impedance shaping is carried out for the grid-connected current loop control, and the parameter design process is given. An approximate high-frequency negative damping offset is achieved by modifying the control loop to enhance the stable operation capability of the system. Finally, the effectiveness of the proposed method is verified with Matlab/Simulink.