Xiaohui Qin

Study on the development and reliability of HVDC transmission systems in China

Over the past decade years, China has seen rapid development in HVDC technologies with the world highest operational voltage of ±800kV commissioned in 2010. By 2013, there are more than 24 HVDC transmission projects commissioned or in operation across China to facilitate bulk transfer of power from western and northern parts of the country to the load centres in the central or eastern regions. A majority of HVDC projects land in the central, eastern and southern grids of China. Reliability of HVDC systems and their interaction with AC transmission systems have become a major concern to the system operators in the State Grid Corporation of China (SGCC) and China Southern Grid (CSG). This paper presents the latest development and future trend of HVDC transmission systems in China. It describes the commutation failure mechanism of HVDC systems and analyzes historical HVDC commutation failures reported in China. Finally the paper presents the reliability analysis of HVDC transmission systems and their impact on hybrid AC/DC system performance.

Study on power system disturbance identification and location based on WAMS

It is extremely important to identify disturbance type and locate where it happens for timely and effective implementation of power system emergency control. However, as for current stability control system, its perception range of disturbance depends on the configuration of measuring points, thus the accuracy and redundancy of disturbance identification are not satisfied. On the basis of analyzing the mechanism of familiar disturbances in detail, a wide area measurement system (WAMS) based approach to identify and locate power system disturbances is proposed. On the one hand, the proposed method selects the PMU-measured disturbed positive sequence phasors of branch currents as characteristic variables, on the other hand, by use of superposition principle, the estimated disturbing components in branch currents are solved in component network. By means of fast matching between measured characteristic variables and estimated disturbing components of presupposed event, the fast and effective identification of the type of disturbance and the position where it happens are implemented to improve the identification and matching of fault scenario of stability control system. Simulation results show that the proposed approach can identify and locate most of disturbances effectively and quickly.

Study of the application of active power adjustment and control technology based on modem energy storage into power system stability control and voltage adjustment

With the planning and constructing of smart grid and the development of energy storage technology in worldwide, it is significant and urgent to study the power system adjustment and control technology based on energy storage comprehensively and thoroughly. It should be noticed that, because of the rapid development of energy storage technology, the fast adjustment and control technology based on active power is becoming realizable and convenient, compared with the popular adjustment and control based on reactive power, such as SVC and STATCOM. In this paper, firstly, the concept and characteristic of active power adjustment and control technology based on energy storage are proposed. Secondly, the applications of active power adjustment and control technology into the power system stability control (including transient stability and dynamic stability) and voltage adjustment arc described. Thirdly, the principles, control strategy and advantages of active power based power system stability control and voltage adjustment is analyzed. At last, the electro-mechanical model of active power adjustment and control based on energy storage is developed, and some demonstrated simulation cases are carried out. The analysis of the simulation results is helpful to configure the capacity and the main control parameters of energy storage devices to realize power system stability control and voltage adjustment.

Dynamic State Estimator Based on Wide Area Measurement System During Power System Electromechanical Transient Process

The wide area measurement system (WAMS) developed rapidly in recent years [1-3]. It has been applied to the studies on many topics in monitoring and control of power systems. But as a kind of measurement system, WAMS has the measurement error and bad data unavoidably. The steady measurement errors of WAMS have been prescribed in corresponding IEEE standard [4], but the dynamic measurement errors now become the focus of discussion [5-6] and attract the attention of PSRC workgroup H11. If the dynamic raw data is applied directly, the unpredictable consequence will be resulted in, which will do a lot of damage to power systems. Therefore, the dynamic estimation for the state variables during electromechanical transient process is the backbone for WAMS based dynamic applications and real-time control.

Self-organized Critical Characteristics Analysis Based on Complex Network Theory

The distribution of line load rate and the nodes inhomogeneity to withstand the transmission of power will have an important impact on the self-organized critical state of the system. For the characteristic of load rate distribution of transmission lines, an improved average semi-variance index is used to characterize changes in the self-organized critical state of the power system. Simulation calculations show that under the same nodal power flow distribution, the larger the value of the average semi-variance, the higher the probability of a large-scale power outage. The curve of probability distribution of blackouts obtained by simulation shows that with the increase of variance value, the tail gradually rises, and the system tends to evolve in the self-organized critical state. The improvement of the average semi-variance index has a good identification effect on the system state after the cascading failure.

Capacity planning of battery energy storage system within wind farm

The capacity planning of a battery energy storage system (BESS) in a wind farm is proposed, which considered a coordinated operational dispatch strategy for a wind farm with BESS. The planning objective is based on the minimum deviation value of wind farm power output as referenced. The most significant advantage in the proposed model is that the lifetime of BESS and forecasting error of wind power are considered. The planning model finally can be resolved by the particle swarm optimization. The case studies are used to validate the performance of the proposed model.

Study on risk assessment for power transformer

Power transformer is one of the key equipment of power grid. The quality defects of power transformer are inevitable for the long cycle manufacturing period with complex technology and artificial factors, which will affect the safety and stability operation. It has great significance to study on quality risk assessment of power transformer. With the manufacturing supervision information source, the quality risk assessment method for power transformer based on fault tree analysis is put forward. The quality risk model with five layers is established, where the manufacturing process risk model is analyzed emphatically. The risk probability is structured based on statistics with abundant history data. The relative probability of the risk event is calculated. The relative weight of risk event is calculated based on fuzzy analytic hierarchy process method. The feasibility of the method is verified by real example. The result shows that the method is easy to understand and convenient for application.

Study on sampling inspection theory and strategy for distribution transformer

In recent years, the manufacturing industry of distribution transformer (DT) in China develops rapidly with high competition. Since the pass rates of National Surveillance Sampling in China (NSSC) for DTs keep a low level, the quality is worried. During the 13th Five-Year Plan period, the investment of distribution network construction will reach 1.7 trillion RMB, which makes a big market for DTs. It is significant to study on optimization of sampling inspection mode and strategy, which can improve the efficiency, quality level, and the reliability of power supply. The research status and theory of sampling inspection are analyzed. The sampling action mechanism is analyzed based on game theory, where the quality cost theory is put forward. The quality cost model with zero-defect is analyzed. The key factors of the sampling inspection for DT are analyzed, including the risk, maneuverability, and economics of the test item. The optimization method of sampling inspection mode is proposed, where three sampling inspection modes are given out. The strategy with dynamic adjustment is put forward. The index system of sampling inspection is designed, which can reflect the efficiency objectively. Finally, the method is verified by the real examples.

Study on the physical mechanism and the fast algorithm of ATC constrained by transient stability for the point-to-grid transmission system

With the planning and constructing of UHV grid in China, some huge thermal plant bases are going to be connected to the receiving grid via UHV transmission lines. Therefore, it is significant and urgent to study the ATC (available transfer capability) of the point-to-grid transmission system quickly for each connection scheme in planning stage. In the paper, firstly, the physical mechanism of ATC constrained by transient stability is analyzed in depth. Secondly, the analytical solution of the ATC constrained by transient stability is proposed on the basis of the physical mechanism analysis. Thirdly, a fast feasible algorithm of the ATC constrained by transient stability is proposed, and the algorithm is independent of the electro-mechanical time domain simulation software. At last, the result of the proposed algorithm is compared with that of the conventional algorithm for the given point-to-grid UHV transmission case, and the correctness and the effectiveness of the proposed algorithm are verified.

Transmission-line theory based study on voltage distribution along the line and the disposition scheme of series capacitors of UHV transmission lines with series capacitors

In this paper, the transmission-line theory based fast algorithm for voltage distribution along the UHV transmission line with series capacitors is proposed. Firstly, the two-port transmission parameter matrix of UHV transmission lines is transformed to the two-port node admittance matrix, therefore, the lumped parameters of strict equivalent π model for UHV transmission line is obtained. Secondly, the parameters are filled into the commercial power flow software to calculate the power flow of the target grid which includes the UHV transmission lines with series capacitors. Thirdly, the power flow calculation results are regarded as the terminal conditions of the UHV lines with series capacitor, and the transmission parameter matrix is used to calculate the voltage distribution along the line rapidly. In the algorithm, the voltage distribution along the line is obtained accurately; moreover, the reactive power supply capacities of both sides of the UHV lines with series capacitors can be taken into account, which implies that the engineering applicability of the proposed algorithm is very strong. At last, the relative disposition scheme of UHV series capacitors and UHV line shunt reactors as well as the centralized/distribution layout scheme of UHV series capacitors are investigated, and some useful conclusions are drawn. According to the proposed algorithm and the conclusions, the guidance suggestion is given for the UHV series capacitors schemes of ‘Wandian Dongsong’ UHV transmission project and ‘Ximeng Waisong’ UHV transmission project.