Zhou Chunxia

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.

Construction of relay protection testing platform for distributed power access to distribution grid

This paper presents the impact of distributed generator (DG) accessing to distribution network on protective relaying at home and abroad, according to the current situation of experimental research analysis the necessity of test method research. Set up electromagnetic transient model of three common distributed power photovoltaic (PV), doubly-fed induction generators (DFIG) and permanent magnet synchronous generator (PMSG) on PSCAD/EMTDC platform; Set up physical model of three common distributed power photovoltaic (PV), doubly-fed induction generators (DFIG) and permanent magnet synchronous generator (PMSG) in dynamic simulation laboratory. Comparing simulation results of distributed generators electromagnetic transient model and physical model under the same fault conditions and control strategy, verified the validity of the laboratory physical model. On the basis of the physical model, construct dynamic test system to test protective relaying for distributed generators access to distribution network, which can realize closed loop for relay protection device from every manufacturer. At the same time test results laid the foundation for the improvement of the existing distributed power relay protection device and put forward the new principle of relay protection.

Fault identification method during oscillating based on negative sequence directional element

The conventional percentage differential protection has been widely used in relay protection, but its operating characteristic will be affected badly when internal fault occurrs during power system oscillating, the differential protection will delay dozens or even hundreds of milliseconds action. Regarding the percentage curve as the research starting point, this paper investigate the relationship between differential current and restraint current when fault occurred during power system oscillating, and points out that when internal fault occured during power system oscillating, the percentage restrained characteristic is the cause of delayed action of differential protection. In order to solve this problem, the differential protection studied in this paper is no longer using the percentage restrained characteristic to distinguish internal or external fault, but using the negative sequence directional element to distinguish internal or external fault. Thinking common double lines as an example, through the study on the characteristics of negative sequence current distribution in double lines, this paper put forward a new kind of fault identification method with using both sides of negative sequence current direction to discriminate whether an internal or external fault occurred, relative to conventional negative sequence power direction element, the discriminant performance is improved greatly, with good district internal and external fault identification, and is not affected by the amount of voltage. Through the synthesis of the negative sequence current, the method is effectively extended to various types of differential protection. Finally, through the modeling and kinds of faults simulating, especially oscillating testing when fault occurring at internal and external area. The simulation results show that the method of fault zone identification is good, the negative sequence directional element can significantly improve the action speed of the differential protection when internal fault occurred during power system oscillating, and at same time the differential protection will not act reliably during external fault.