Jinghan He

Research on adaptive protection based on integrated protection

Generally, the three-stage current protection and the instantaneous under voltage protection with current supervision are set to protect the low-voltage distribution system. The protection range of adaptive current instantaneous protection, irrelevant to the fault type of the power system, will be affected by the different operating mode of the system. When the parameters of power system satisfy certain relations, the minimum protection range will be less than 20% of the line length. The adaptive current instantaneous protection can not to be used in this case. This paper presents an approach to solve this problem by combining the adaptive current instantaneous protection with adaptive voltage instantaneous protection.

A centralized protection scheme based on combined positional protection techniques

This paper presents a new protection scheme for high-speed protection of transmission lines, the Integrated Positional Protection scheme. The concept of integrated protection is firstly introduced, in which a centralized protection relay provides the protection for multiple transmission lines. The proposed scheme is based on a specially integrated relay unit, which is installed at each substation of a network and responsible for the protection of all the line sections associated with the substation. The relay based on the detection and processing of fault generated high frequency transient current signals incorporates two novel protection principles and their application techniques, which are the positional protection techniques with and without the synchronization of Global Positioning System (GPS) respectively. The technique without the need for GPS synchronization is a non-unit protection technique, which does not require a communication link. The decision to operate is based on the detection of the relative arrival times of these high frequency components at the relay location as they propagate through the system. The basic principle of the GPS based technique is to detect the fault generated high frequency transient signals and record the time instant corresponding to when the initial travelling wave generated by the fault arriving at that busbar. A communication gateway is used to transmit and receive coded digital signals of the local information to and from the associated relay(s) in the system. At each substation, the relays determine the location of the fault by comparing the GPS time stamps measured locally with those received from the adjacent substations. Simulation studies of the scheme were carried out to examine the response to different power system and fault conditions. Results show that the scheme is insensitive to fault type, fault resistance, fault inception angle and system source configuration, and is able to offer both very high accuracy and speed in fault detection.

Optimal Control Strategy of Electric Vehicles Based on the Adaptive Mutation of PSO Algorithm

The development of technology concerned of electric vehicles and the expansion of Charging facilities scale, researching on Vehicle-to-Grid (V2G) technology has been increasing concerned in recently. Not only taking power from the grid to charge the batteries on these vehicles, but the power could also be transferred into the grid from their batteries when parked, which is known as Vehicle-to-Grid(V2G) concept. The key research technique is proposing a control strategy for scheduling usage of available energy storage capacity from electric vehicles reasonably and effectively in a certain scale plot. This paper establish the mathematical model which concludes two constrain conditions to simulate electric vehicles level the load curb. Then a new adaptive mutation particle swarm optimizer, which is based on the variance of the populations fitness is presented. A critical adaptive mutation operator is put forth in this algorithm in which mutation probability is decided according to the variance of the populations fitness and the current best solution, which improve the ability of algorithm to break away from local optimum. The last, example results show applicability and effectiveness of the algorithm which schedule vehicle for leveling a load curb.

Design of adaptive optimal reclosure based on digital substation network

This paper presents a new scheme for power line autoreclosure technology, the integrated adaptive optimal reclosure. The background of the development is firstly outlined and the basic principles of these new techniques are described. These include the adaptive reclosure and the optimal reclosure techniques. The new scheme proposed is based on the latest development in digital substation, in which the proposed new techniques are implemented into a specially designed integrated reclosure device, which is responsible for the protection of a number of line sections associated with the substation. Studies show that these new developments offer potential for significantly improving the performance of the power system protection and control.

Active Control of Power Flow in Distribution Network Using Flexible Tie Switches

To accommodate high penetration of distributed generation (DG), the distribution network is moving towards the direction of active control and active management. This paper presents a new type of flexible tie switch (FTS), installed in place of traditional sectionalizers or tie switches, which can be applied for active power flow control in a distribution network. FTS can potentially optimize the existing network capacity so as to accommodate more DGs. In order to analyze its effectiveness, the simplified mathematical model of FTS in dq coordinates was first derived. The dynamic power control performance of FTS was studied in PSCAD with typical dual closed-loops control algorithm adopted. Minimum network losses and voltage profile optimization were set as the goal of power flow control. Multi-objective optimization function which takes FTS as control variable was built, considering voltage deviation constraint, capacity limitation of FTS and its power losses. Hybrid particle swarm algorithm was used to search for optimal solution under different load level conditions. Results show that the network losses are reduced significantly and the voltage profile is also optimized, when FTSs are used for power flow control in a distribution network.

Simulation of Transient Skin Effect of DC Railway System Based on MATLAB/Simulink

This paper presents a technique for simulation of transient skin effect of the dc railway system based on MATLAB/Simulink. The classic calculation of skin effect based on frequency domain is not suitable for time-domain simulation. The aim of this paper is to develop a time-domain calculation method which can be realized in MATLAB/Simulink. Through the analysis of the step series algorithm, results are applied to the calculation of frequency voltage signal and compared with skin effect impedance of frequency. Accurate simulation of the transient skin effect produces accurate modeling of the remote fault current. This is important for the dc railway protection researchers to develop techniques for discriminating remote short-circuit currents from locomotive starting currents.

Modeling and Simulation of Metro DC Traction System with Different Motor Driven Trains

This paper presents two comprehensive models of DC subway traction system to simulate the starting-up process using Matlab/simulink. One is DC motor driven, the other is AC motor driven. The model includes substation rectifiers, the track and the different driven subway trains. The objective of the model is to study the short circuit faults and the train starting current. Analysis and conclusion of simulation results are given, which pointed out the difficulty of discrimination remote short circuit current against train starting current.

Developments in digital simulation of traction transformer

This paper studies the modeling and simulation of Scott Transformer to investigate the transient behaviors of traction system. The paper presents an equivalent model of Scott Transformer, which can be used to simulate normal operation, internal fault and excitation inrush of the transformer. The model combines both the Scott Transformer and the Auto transformer, which are widely used in AT power supply for traction systems. The studies show that the model presented is correct and results from simulation is able to provide useful information for researchers and engineers in assessment, design and implementation of protection systems.

Parallel line integrated protection based on transient current polarity comparison

A parallel line integrated protection technique based on transient current polarity comparison is presented. An integrated protection relay interfaced to both CTs of the parallel lines, is responsible for the protection of the parallel lines. The polarity ofthe transient current component which comes from the faulted direction on the transmission line is different from the one which comes from the other emanating lines. Protection using this principle can protect not only all lines associated with a busbar, but also the emanating parallel lines. The paper outlines the potential problems, design and implementation of the parallel lines integrated protection based on transient polarity detection using wavelet transform. Simulation studies show that it is feasible to realize the parallel lines integrated protection utilizing the polarity of the transient current component.

Transformer Protection Based on Fault Transient Detection

This paper presents a new relaying scheme based on the polarity comparison for power transformer protection. Wavelet transform presented in the paper is sued for extracting the transient signal feature of the internal and external fault current waveform, the paper then presents a criterion, which can reliably distinguish between internal faults and inrush currents. All the conclusions are verified by simulation using the EMTDC, the experimental results indicate that this technique is effective under various fault conditions.