Abstract Amidst the escalating demand for energy and the proliferation of renewable energy sources, direct current (DC) systems have garnered increasing interest. As pivotal for the safety and reliability of DC systems, testing DC circuit breakers is a critical step to evaluate their performance and dependability. This study focuses on the breaking test method for medium and high-voltage DC circuit breakers. It compares and evaluates the current waveform, recovery voltage, and energy dissipation across various test circuit methodologies during the breaking process of DC circuit breakers and assesses the suitability of test methods across different voltage levels.

This paper proposes a hybrid HVDC transmission system using the diode rectifier unit (DRU) at the sending end and the voltage source converter (VSC) at the receiving end. To solve the problem of the lack of regulation capability in the converter station at the sending end, a scheme is proposed to replace traditional converter transformers with flexible transformers at the sending end based on the operating characteristics of diodes. Then, this paper designs the basic control strategy of the system, including flexible transformers and MMC at the receiving end. Subsequently, an equivalent simulation model of ±10kV/10MW is built in the electromagnetic transient simulation software, and typical scenarios such as power step and AC faults at the sending end are simulated to verify the effectiveness of the proposed hybrid HVDC transmission system and its control strategy.

The excessive short-circuit current restricts the development of the power grid. By using the fast switch to dynamically change the system topology structure during faults, the short-circuit current flowing through the conventional circuit breaker can be limit under the switchable current range, but the application of fast switch will affect the relay protection. In this paper, the flexible short-current suppression technology using the fast switch is introduced firstly. Then, the influence of fast switch on line protection, differential protection, distance protection and zero-sequence protection is discussed, and the optimized protection strategies are proposed. Finally, the simulation result is verified in RTDS.

High voltage shunt reactor((referred to as HSR, the same below)) is an important equipment used to absorb reactive power and limit overvoltage level in power system. Its frequent fault is inter-turn short circuit of winding. The traditional inter-turn protection based on the principle of zero sequence component has been maloperation for many times on site. Based on the analysis of the structure and electrical characteristics of HSR, this paper defines the root cause of the maloperation of traditional inter-turn protection, and puts forward a new type inter-turn protection scheme for HSR, which composed of core saturation criterion, zero sequence power direction criterion and zero sequence impedance criterion. The experimental and operation results show that no matter whether the core of HSR is saturated or not, this scheme can ensure that not only not operate reliably when air-drop without fault, but also operate sensitively and reliably when there is more than 2% inter-turn short circuit fault, so as to solve the problem of maloperation of traditional inter-turn protection due to core saturation.

In order to avoid the adverse effects of the access of renewable energy sources on automatic reclosing, reclosing is usually done by cutting out renewable energy power supply after the fault occurs and extending the reclosing setting time. But this will lead to the interruption of power supply to a large number of local loads, which is not conducive to the efficient use of renewable energy sources. In this paper, a new reclosing method for substation lines with inverter-type renewable energy source access is proposed. This method can keep the inverter-type renewable energy source running continuously during reclosing, and ensure the continuity of power supply of important loads. Firstly, it is pointed out that the control strategy of renewable energy source must be switched during reclosing, to make it have the basic island operation capability. Then, to maintain the power balance between renewable energy source and load, the method of using load shedding cooperating with unloading resistors during reclosing is proposed. Finally, the reclosing operation will be performed when the synchronization conditions are met. And simulation under different working conditions is carried out on PSCAD/EMTDC platform, which verified the feasibility of the proposed reclosing strategy.

5G has the characteristics of high speed, low delay, interconnection of all things and low power consumption. The application requirements of the power industry are highly matched with the technical characteristics of 5G. The three technical features of 5G provide differentiated network service capabilities for different businesses of the power grid, and bring new opportunities for the transformation and upgrading of the power industry. 5G mobile communication technology has a wider range of applications. The application of relevant technologies in the power communication system can improve the shortcomings of the power communication system and bring far-reaching changes to the power industry. This paper introduces 5G and its application in power industry, analyzes the characteristics of business model, and further discusses the business model of 5G in power industry.

This paper introduces the research and development of a novel substation-area protection, which is applied in the intelligent substation based on IEC 61,850. This protection device can subscribe the multi-source information through the SV/GOOSE network. The device structure is modularized. Each plug-in can realize an independent protection function and can support plug and play. With the application of the multi-bay information, the protection can provide multiple protection functions in a centralized approach, such as the fast backup protection, the centralized re-closing function and the circuit breaker failure function. The protection can also cope with the situation that the CT/PT secondary loop broken faults. This substation-area protection technology is help to improve the performance and the reliability of the protection. In addition, the centralized protection structure can effectively reduce the secondary loop, which is easy for operation and maintenance. This protection device has been put into application in a 220 kV substation.

In order to promote the practice on the DG (distributed generation) technology, this paper introduces the theory research and engineering practice on the protection and control method of the DG system, based on an IDC DG engineering. The basic information and the characteristic of the engineering is described. The general control target and the operation mode under different condition is analyzed, considering the operative characteristics and the requirements of the power substation, the DG and the customer. The coordination scheme between the power grid, the DG and the load is proposed innovatively. The priority and the logical sequence of the control from different part are determined. The practical experiment proves that the protection and control system can provide reliable and efficient power and refrigeration supply for the IDC data central via the coordinated control method of the operation mode shift, SPAS (spare power automatic switchover), load transferring and the black-start, with the coordination of the power grid, the DG and the load. Under the extreme case that the outside power is totally lost, the power and refrigeration supply can be recovered within 155 seconds.

Based on the concept of multi-resolution morphological gradient (MMG) in mathematical morphology, a new scheme of single-ended transient protection is proposed. On the basis of MMG, the window function energy spectrum of the transient current signal generated by the fault is extracted to realize the identification of faults in the area and outside. A typical 500 kV EHV transmission line is selected and simulated by PSCAD/EMTDC. The results show that the scheme is not affected by fault type, fault location, transition resistance and initial phase angle. At the same time, the calculation amount of the algorithm is smaller than that of the multi-scale wavelet transform, which is beneficial to engineering implementation.