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Guo Y.,China Electric Power Research Institute | Liu H.,Central China Grid Company Ltd | Wang X.,China Electric Power Research Institute
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2017

For zero sequence current differential protection phase selection element influenced by load current leading to low sensitivity in high impedance ground fault conditions, this paper puts forward a zero sequence differential protection phase selection element based on the sequence component. The phase selection element consists of three parts: to distinguish between single-phase grounding fault and two-phase high impedance ground fault using the similarity in strength of negative sequence to zero sequence differential; using phase relationship between positive sequence and negative sequence differential current to distinguish between single-phase grounding fault and two-phase grounding fault; using differential criterion of low restraint coefficient to prevent unbalanced zero sequence current by outside three-phase short circuit. A simulation model is developed and verified in RTDS, the results showing that: the phase selection element proposed is not affected by overload, can accurately select single-phase grounding fault without compensation, and ensure the higher sensitivity than zero sequence differential protection to trip out the faulty phase of zero differential protection. © 2017 Automation of Electric Power Systems Press.


Wu T.,Hubei Engineering University | Ruan J.,Hubei Engineering University | Hu Y.,State Grid Electric Power Research Institute of China | Liu B.,Central China Grid Company Ltd | Chen C.,Hubei Engineering University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2011

Forest fires near power transmission lines always threaten the reliability of transmission lines and safety of power grids. Combining video record of the 500 kV transmission line fire induced flashover and breakdown characteristics of rod-plane gap under wood crib fires, the flashover mechanism of 500 kV line under forest fires was investigated. Results are as follows: the dielectric resistance increases with the height of flame due to temperature that affects the thermal ionization of alkali mental salts; the breakdown strength of rod-plane gap under wood crib fire is reduced to 23% of that air gap under standard atmosphere; flame temperature, conductivity and particles such as smokes and flying ashes promote the electronic avalanches and streamers development and lead to the dielectric strength reduction of the transmission gap acutely; pre-discharges initiated by flying ashes and smoke are connected to flame tip and promote the burning of fire. Electrical arc enhances the fire intensity and lifts the height of flame. Based on field records and experimental results, it is concluded that flame temperature, flame conductivity and flying ashes are ascribed to factors leading to transmission line flashover due to fire. Measures to reduce transmission line breakdown under forest fire such as increasing height of transmission line conductors above ground, restricting the vegetation species, height and density near transmission line corridors are proposed. © 2011 Chinese Society for Electrical Engineering.


Liu H.,Central China Grid Co. | Jia X.,State Grid Electric Power Research Institute of China
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2011

By proceeding from the implementation of the digital algorithm of relays, a discussion is made of the contradiction between the action speed of rapid relays and the length of data window. In order to solve the contradiction, various algorithms are adopted for relays. Short data window algorithms are fast and long ones are accurate. The long data window full wave Fourier algorithm is selected to ensure the accuracy of the calculation and simplify the Fourier algorithm used in variation relays. The operation equation of amplitude comparison relays of rapid relays is expressed as the operating value being greater than the braking value. To meet the requirement on the variation relay to serve as the rapid relay, the braking coefficient is introduced into the braking value according to the variation features of the operating value to correct the operation characteristics in real-time so as to meet the requirement of action speed. © 2011 State Grid Electric Power Research Institute Press.


Patent
State Grid Corporation of China, Hubei Electric Power Company and CENTRAL CHINA GRID COMPANY Ltd | Date: 2016-05-10

The invention relates to a parallelization method for black-start subsystems of a power grid with external support, which includes, after power blackout, partitioning the power grid into subsystems, and respectively performing black-start on the subsystems based on a power grid black-start research scheme, performing stability check on each subsystem, performing voltage calculation on parallel lines between the subsystems, checking the parallelizing simulation of the subsystems, and determining a feasible parallelizing path and a recommendable charging direction. The method further includes, starting from the subsystems having external support and higher stability, networking them with an external power grid, parallelizing the networked subsystems having external support to obtain a subnet of the subsystems, parallelizing subsystems having no external support with the subnet of the subsystems to obtain a regional subnet, and finally parallelizing the remaining subsystems with the regional subnet to implement parallelization of black-start subsystems of the whole power grid.


Li F.,Central China Grid Co. | Xie J.,Central China Grid Co. | Zhao Y.,Wuhan Zhongyuan Huadian Science and Technology Co. | Zhang X.,Wuhan Zhongyuan Huadian Science and Technology Co. | And 2 more authors.
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2012

By analyzing the main functions, i.e., data exchange and time synchronization of the switch in smart substations, the information model of switch intelligent electronic devices (IEDs) based on IEC 61850 standards is built. The information model consists of three logical devices (LD) such as: common LD, data exchange LD and time synchronization LD. Moreover, a new group of logical node class model is put forward in order to describe switch operation status and configurable parameters with different communication network protocols. Finally, several discussions are given for further modification of the proposed information model. © 2012 State Grid Electric Power Research Institute Press.


Liu H.,Central China Grid Company Ltd | Zhou Z.,China Electric Power Research Institute
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2011

Existing distance protection of transmission lines depends on setting calculation to avoid operation under over-load conditions. After operation of distance protection, the line load transferring to other transmission lines may result in fault expansion, so it's necessary to find some new countermeasures to avoid the mal-operation of distance protection in post-fault over-load condition. This paper proposed a new criterion to identify between over-load and fault in voltage co-ordinate instead of that in impedance co-ordinate. In the criterion, an operation area was constructed by considering compensation voltage as operation voltage and the polarization voltage as reference voltage. The protection will operate when the operation voltage is in the operation area. In the voltage co-ordinate, the load voltage is on the line between the two power source voltages, so it's easier for the protection to decide whether operate or not. The criterion can identify between fault and over-load radically and make distance protection avoid mal-operating after the load transferring. Its application will be benefit for the stability of power system. Simulation results show that the method is effective. © 2011 Chinese Society for Electrical Engineering.


Liu H.,Central China Grid Company Ltd | Li Y.,Huazhong University of Science and Technology
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2010

The three elements of distance relay in the voltage plane are the polarization voltage, operation voltage and operation characteristic, among which the polarization voltage is the most important. The relay could ideally select pre-fault voltage as polarization voltage, while it practically employs the positive sequence voltage. The difference between the two kinds of polarization voltage is negligible in the case of low impedance ground fault, while significant in the case of high impedance ground fault. Thus, this paper uses the memory and the non-fault phase parameters to gain the pre-fault voltage, and use it as the new polarization voltage. Thus it puts forward a new self-adaptive high impedance ground distance relay. The theoretical analysis and simulation result show that the performance of the distance relay based on the voltage plane is better than that based on the impedance plane. © 2010 Chinese Society for Electrical Engineering.


Xu D.,China Electric Power Research Institute | Xia S.-L.,Central China Grid Company Ltd | Ding Q.,China Electric Power Research Institute | Ma Z.-M.,Northeast Dispatching Branch
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

Single mixed-integer programming (MIP) method is hard to obtain satisfactory solution in reasonable time when it solves large-scale unit commitment problems (UCP). In order to solve the problem, we propose a heuristic MIP method. Based on the unit on/off inherent mechanism, this algorithm determines the part of integer variables based on priority list method by comprehensive analysis of load curve and unit on-off characteristics. MIP method is combined to solve large-scale UCP, which can expand calculation scale and accelerate the calculation speed. The improved MIP is tested on standard and actual system and compared with existing reference. The comparison results prove the correctness, validity, and practicability of the proposed algorithm.


Xiong G.,Huazhong University of Science and Technology | Shi D.,Huazhong University of Science and Technology | Zhu L.,Huazhong University of Science and Technology | Chen X.,Central China Grid Co.
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2014

A fuzzy cellular fault diagnosis method of power grids based on the radial basis function neural network is proposed for solving the transportability problem of adapting to the network topology changes when applying neural networks to fault diagnosis of power grids. This method takes single line, bus and transformer as a cellular object, and takes all the associated protective relays (PRs) and circuit breakers (CBs) used to protect the cellule as inputs to develop a generalized cellular neural network diagnostic model. Moreover, a method for automatic generation of the diagnostic model during fault diagnosis is presented. In addition, taking into account the fault information's characteristic of incompleteness and uncertainty, a fuzzy sagittal diagram for each cellular type is adopted to describe the logic reasoning relationships between the components, PRs, and CBs. From the diagram, multiple fuzzy reasoning rules containing uncertainties can be extracted to train the generalized cellular neural network. The simulation results show that the proposed method is simple, efficient, and can solve different complex faults. Moreover, it can effectively adapt to network topology changes and has good fault tolerance and transportability. © 2014 State Grid Electric Power Research Institute Press.


Shu X.,Central China Grid Company Ltd
Journal of Computational Information Systems | Year: 2012

Relevance vector regression, based on Bayesian evidence framework, is a nonlinear probabilistic model. Generalization performance of relevance vector regression is comparable to that of support vector regression. In order to solve the QP problem of traditional relevance vector regression effectively, a robust relevance vector regression algorithm is proposed to predict electricity consumption in the paper. Electricity consumption of a certain province from 2008.12.1 to 2008.12.31 is used to test the performance of the robust relevance vector regression model.In the process of training the robust relevance vector regression model, we employ the relevance vector regression models with the different dimensional input vector to find the optimal robust relevance vector regression model. It can be seen that the robust relevance vector regression model with 5-dimensional input vector has the best prediction effects among all the relevance vector regression models, and the prediction effects of the robust relevance vector regression model are better than those of the support vector regression model. © 2012 Binary Information Press January 2012.

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