Du Dingxiang

Modeling and simulation research of large-scale AC/DC hybrid power grid based on ADPSS

With the continuous increasing load and construction of UHV, A plurality of EHV / UHV AC and DC transmission lines centralize in the load center. In order to analyze the interactive effects of AC or DC system when fault occurs, a hybrid simulation model on electromechanical and electromagnetic transient process of AC and DC is established for regional power grid. The electromagnetic transient model covers the EHV / UHV AC and DC transmission lines, EHV / UHV transformer and lots of generators. Various faults are simulated in four network partitions, including all kinds of AC and DC transmission faults. On the basis of simulation, the characteristics and interactive effects of AC and DC system is studied. Research results suggest that for load center with both DC and AC, AC system faults will cause multiple HVDC commutation failure, thereby affecting the performance of AC relay protection. For the power grid closely connected, the DC system blocking will not cause any problem on system stability.

A combined phase selector element based on the superimposed sequence components for parallel lines on the same tower

The traditional fault phase selectors which have excellent performance for single-circuit transmission line may mis-operation for some cross country faults in parallel lines on the same tower. Based on the analysis of faults in parallel lines, a novel combined phase selector based on the one-end sampling data of a single line is proposed. Assume that parallel lines as the overall analysis of the object, the sequence voltages are employed to determine the fault phase. The relationship between the superimposed positive- and negative- sequence impedances are employed to determine that the fault occurs either in line I or line II. According to the phase selector, the phase selection can be achieved in parallel lines on the same tower, especially in cross country faults. Therefore, the distance relay can be achieved using appropriate equations depending upon the faulted phase identification. Simulation results show that the proposed scheme is well suited for the phase selection in parallel transmission lines.

Impact of the distributed photovoltaic on the current protection of 10kV distribution network

Compared with other distributed generators, distributed photovoltaic (PV) is quite different in the fault characteristics. The impact of the distributed PV on the current protection of the distribution network is still unclear, making it difficult to guide the operation and management of power grid. In this paper, a typical model of distribution network with the distributed PV is established based on PV inverter control characteristics and relevant technical regulations of state grid corporation of China; the influence of the distributed PV capacity on fault currents of the distribution network is also quantitatively analyzed. Moreover, according to relationship between the different capacity of distributed PV and the amplitude of fault current, the corresponding countermeasures are proposed to provide technical support to renovation of relay protection for the distribution grid with high penetration of the distributed PVs.

A new protection technology for smart distribution network

Because of the requirements of the accessing distribution generation and the high quality power supply to the protection of smart distribution, firstly, the drawbacks are analyzed to the existing stepped protection of distribution network; secondly, a new protection with multiple types of data based on the serial communication is proposed. The proposed protection achieves the new algorithm with the function of closed-loop control via the communication technology. It has the ability of following the changing structure of the tracking system to be protected, and also has the ability of achieve the reconstruction capabilities of the protection functional in the secondary equipment failure. So, it can achieve a high-performance protection.

Dynamic simulation inspection test for protection equipment in China

Testing the protection equipment on dynamic simulation test systems is very valuable not only for finding software bugs and design deficiencies of protection but also for performance and characteristics understanding. To strictly test different kinds of protection relay, the test systems must been designed carefully by selecting the connection and parameters of the system. The test items are designed specially for every kind of protection. This paper introduces some special technical requirements in China, and important test items for different protection schemes. Several ideas and algorithms of some protections are also compared in this paper, such as power swing blocking methods in line protection, current transformer saturation countermeasures in transformer and busbar protection, inrush currents, blocking methods in transformer protection, current transformer single-phase open detection methods, etc. Several problems appeared in the test and the reason of these problems are described and analyzed in this paper.

A phase selection element for zero sequence current differential protection

A phase selection method for zero sequence current differential protection was proposed in this paper. In the first, electrical quantities characteristics of different ground faults were analyzed. Then zero sequence differential current was used as reference value and sizes of sequence differential currents and zero sequence differential current were compared to identify fault phase. Phase differential current was used to identify healthy phase of two phases to ground faults, theory analysis and simulation results show that the phase selection criterion can identify fault phase correctly and is not affect by load current and fault resistance. It is more sensitive than zero sequence current differential protection.