Shaofeng Huang

Wams Based Flow Transferring Indentification Algorithm and its implementation

When relays trip a faulted line in power system, the flow on the faulted line will be transferred to the other lines. Those lines might be overloaded and then cascading tripped by the backup relays, which worsen the system state and even cause blackout. Generally, these kind of cascading trips are the origins of a lot of well-known blackouts. In this paper, by analyzing the defects of traditional backup protections, a new wide area backup protection scheme based on WAMS is presented to identify flow transferring. A new concept of flow transferring relativity factor (FTRF) is proposed to estimate the flow distribution after flow transferring occurs; and the method of calculating FTRF matrix online is also deduced. The simulation of 10-unit and 39-bus New England network shows that the proposed wide area backup protection scheme can identify flow transferring successfully and hence be superior to the traditional backup protection.

Relay replacement strategy based on the least unit life cycle cost with minimum maintenance model

Protection device is repairable system, and its routine maintenance is Minimum Maintenance. With the number of maintenance increasing, both the reliability of relay and the economy of maintenance are decreasing. Therefore, it should be replaced at a proper time. The optimal replacement strategy was studied based on relay reliability and maintenance economy according to field data. It first constructed a minimum maintenance model. Then, based on the constructed model, it formulated the replacement strategy as an optimal problem with the objective of least unit life cycle cost. Finally, it obtained the optimal replacement cycle for a field-operating relay with the proposed strategy. In addition, in order to simulate the actual situation with more accuracy, it considered the double protection in the proposed strategy.

Researches on the time-varying failure rate characteristic for the HVDC protection devices in China Southern Power Grid

In China Southern Power Grid (CSG), the SIMADYN D (SD) of SIEMENS plays an important role for the HVDC protection system. Based on the field failure data of SD, this paper studies the time-varying failure rate (TFR) characteristic for the protection devices of HVDC in the CSG. According to the concept of TFR, failure mode is divided into two types, one is the aging failure and the other is the random failure. According to the above failure classification, the failure characteristic of different modules is also discussed.

A methodology for vulnerability assessment of backup protection under cascading failures

To avoid undesired operation of backup protection caused by load encroachment under cascading failures, the methodology for vulnerability assessment of backup protection is studied. In this paper, the vulnerability assessment of backup protections is formulated as a mixed integer nonlinear programming problem, which is solved by the binary particle swarm optimization approach. The measurement index for assessing the vulnerability of backup protection is given as well. The simulation results on New England 39-bus system demonstrate that the proposed method can effectively assess the vulnerability of backup protection under cascading failures.

Reliable coefficient analysis and exploration of phase-to-phase distance protection for short line

Aiming at the situation that distance protection is applied to short lines, impedance measurement errors caused by factors that influence the phase-to-phase distance protection are analyzed based on the worst conditions. On this basis, the relationship between reliable coefficient of zone 1 phase-to-phase distance protection and length of transmission line is explored. A method of setting reliable coefficient is proposed, which makes the setting of zone 1 distance protection more reliable. It effectively avoids the over-reaching problem. Simulation results with PSCAD show the theoretical analysis is correct.

Analysis on natural main frequency

After the fault of EHV or UHV transmission line, natural main frequency makes the difference with the changing of fault place. The paper analyzes expression of the natural main frequency approximately at the difference fault places. The conclusion is that the nearer the distance of the fault place, the higher the natural main frequency and the farther the distance of the fault place, the lower the natural main frequency. In addition, the natural main frequency is in a range and the natural main frequency is finite. The accuracy of changing curve and the range of the natural main frequency have been proven by PSCAD procedure in a practical UHV transmission line.

A new calculation method for open-phase fault based on superposition principle

According to open-phase fault condition occurred in power system, this paper proposes a new calculation method based on superposition principle. The open-phase fault network is equivalent to the superposition of a disconnection state before faulting and an additional short-circuited state, after calculating the two states respectively and superposition of the results acquired, calculation formula of electric quantity in open-phase fault network can be obtained. In this paper, two kinds of fault during the open-phase running are calculated: fault occurs on the faulty phase and on the sound phase. The formulation of the post-fault electrical quantities is obtained. Numerical examples and the simulation results from PSCAD demonstrate that the proposed method has good effectiveness and feasibility.

Online condition monitoring methodology for relay protection based on self-test information

A microprocessor-based relay protection unit has strong self-test capability that allows the device to monitor operation conditions and diagnose problems by itself. Based on the characteristics of microprocessor-based protection software and hardware architecture, this paper proposed an online health monitoring methodology using the self-test information of protection units. In accordance with expression modes and acquisition methods, self-test Information of protection equipment can be divided into following four categories, state self-test information, analog self-test information, description self-test information and statistics self-test information. Considering all factors affecting the health status of protection units, this paper established a generic evaluation model of health status. The master station for condition monitoring collects self-test information and evaluates the health status of protection unit online, and provides guidance for condition-based maintenance.

Identification of backbone-grid in power grid based on binary particle swarm optimization

Previous blackouts demonstrate that the safe and stable operation of backbone-grid plays a key role in preventing large-scale blackouts caused by cascading failures. Based on binary particle swarm optimization, a novel method is proposed to identify the backbone-grid in power grid. First, the concept of the backbone-grid is defined for mathematically describing the critical lines and important topology structure which are crucial for power system to prevent the blackout caused by cascading failures. On this basis, the problem of exploring backbone-grid is further formulated as a mixed integer nonlinear programming problem which is to be solved with binary particle swarm optimization. The problem just needs to be optimized only once. The backbone-grid essential to the safe and stable operation of power grid can be obtained. Simulation on IEEE RTS-79 system verifies that the proposed method can identify backbone-grid with high computational efficiency.