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Xuchang, China

Bompard E.,Polytechnic University of Turin | Wu D.,Polytechnic University of Turin | Xue F.,XJ Group Corporation
Electric Power Systems Research | Year: 2011

Vulnerability analysis of power systems is a key issue in modern society and many efforts have contributed to the analysis. Complex network metrics for the assessment of the vulnerability of networked systems have been recently applied to power systems. Complex network theory may come in handy for vulnerability analysis of power systems due to a close link between the topological structure and physical properties of power systems. However, a pure topological approach fails to capture the engineering features of power systems. So an extended topological method has been proposed by incorporating several of specific features of power systems such as electrical distance, power transfer distribution factors and line flow limits. This paper defines, starting from the extended metric for efficiency named as net-ability, an extended betweenness and proposes a joint method of extended betweenness and net-ability to rank the most critical lines and buses in an electrical power grid. The method is illustrated in the IEEE-118-bus, IEEE-300-bus test systems as well as the Italian power grid. © 2011 Elsevier B.V. All rights reserved.


Zhang H.-Y.,XJ Group Corporation
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2011

The traditional converter connection-transformer differential protection uses the second harmonic of differential current as the blocking condition of magnetizing inrush current when no-load closing. But it doesn't consider the running condition of no-load closing in the two converter transformer parallel operation. Through the maloperation event of converter connection-transformer differential protection in no-load closing in Yunguang converter station, this paper analyzes magnetizing inrush currents characteristics in the converter transformers, and the synthesizing current characteristics of converter connection-transformer differential protection. It is pointed out that the reason of this event is that the magnetizing inrush current of star transformer and star-angle transformer cancel out each other, which causes an invalid second harmonic blocking criterion. This paper introduces the differential current harmonic blocking criteria of star transformer and star-angle transformer to construct an 'and' logic with the criterion of converter connection-transformer, which solves the problem.


Yi Y.-H.,XJ Group Corporation
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

This paper analyzes the relationship among the concepts of mean time between failures, failure rate and life, discusses the limitations of life research about present relay protection devices, and collects the statistics of relay protection devices' life and failure rate in different time from an electric grid corporation. According to the characteristics that relay protection devices are repairable, and by amending the data of relay protection devices which are untimely out of service due to the present management system, Marquardt method is utilized to estimate the parameter of two-parameter Weibull distribution function of relay protection devices' life, thereby the cut-off of failure rate and the distribution curve function of failure rate are obtained. The paper analyzes the main influence mechanism and proposes the methods to extend the life, so as to provide the theoretical basis for relay protection devices' life requirement.


Wang B.-T.,XJ Group Corporation
Gaoya Dianqi/High Voltage Apparatus | Year: 2010

This paper discusses the DC circuit breaker installed in converter station of HVDC project, focusing on the functional requirements, main performance, basic composition, principle of breaking and test technology. The differences of DC circuit breaker and AC circuit breaker in current conversion, environmental tolerance, and breaking performance, etc. are analyzed, and a formula for calculating conversion current of DC circuit breaker is offered. The results show that selecting reasonable creepage distance of DC circuit breaker insulator is very important for improving the operation level, and zero-crossing point must be created when breaking DC. In addition, this paper also describes different performance tests for both DC circuit breaker and AC circuit breaker to provide a reference for Chinese researchers of high-voltage DC circuit breakers.


Patent
State Grid Corporation of China and Xj Group Corporation | Date: 2012-10-15

The present invention relates to a busbar differential protection method. For each bay, firstly, zero-crossing point of voltage is determined according to sample values of voltage, then the current values are re-sampled on a current fitting curve by using zero-crossing point of voltage as a synchronous signal according to a given sampling time period to get a sample sequence. The sample sequence is comprised of current values of sampling points and sample serial numbers. The sample serial numbers of sampling points at the same time are same for the sample sequence of respective interval. Finally, computing is done to sample sequences of respective intervals, and differential protection is achieved.

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