Tai Nengling

A Transient Harmonic Current Protection Scheme for HVDC Transmission Line

Based on the boundary characteristic of a dc transmission line, the response of transient harmonic current in the line-commutated converter HVDC transmission system is analyzed under various fault conditions in this paper. A new transient harmonic current protection scheme is proposed. The discrete Fourier transform is used to extract transient harmonic currents at both terminals of the dc transmission line and the type of fault can be identified by the transient harmonic currents. Two main factors including fault resistance and fault location that affect performance of the protection are also discussed in this study. The test system is modeled based on the CIGRE benchmark including distributed parameters of the dc transmission line. Comprehensive test studies show that the performance of the transient harmonic current protection scheme is encouraging. It can not only identify internal faults and external faults correctly and quickly, but also can respond to high ground resistance faults.

A Transient Protection Scheme for HVDC Transmission Line

The relation between the parameters of dc transmission line and the variation of transient energy has been analyzed under various fault conditions in this paper. According to that, a new transient energy protective scheme is proposed. It is developed based on the distributed parameter line model in which the transient energy distribution over the line can be obtained from the voltage and current measurements at both terminals and the fault can be recognized from the calculated value simply. The test system is modeled based on the CIGRE benchmark and considered the distributed parameters of the dc transmission line. Comprehensive test studies show that the performance of transient energy protection scheme is encouraging. It can not only identify internal fault and external faults correctly and quickly, but can also respond to the high ground resistance fault. Finally, two main factors, including fault resistance and transmission distance, that affect the performance of the protection are also discussed.

An Impedance Protection Scheme for Feeders of Active Distribution Networks

Distribution networks (DNs) gradually become more active and flexible with the massive integration of renewable resources. The conventional protection methods are unsuitable for the promising active DNs. This paper proposes a protection scheme on the basis of measured impedance, which includes an impedance differential method and an inverse-time low-impedance method. The former approach identifies fault instant and provides time reference for the exchanged data. As primary protection, it is able to clear different types of faults as soon as possible. The latter method operates in an automatic coordination way with inverse-time characteristic. It can be used as backup protection or provide protection for single-end lines alone. Both of the methods are independent of operation modes and are able to clear faults with high sensitivity. The efficiency of the protection scheme is validated by PSCAD/EMTDC.

Wavelet-based ground fault protection scheme for generator stator winding

Abstract A new stator ground fault protection scheme is introduced in this paper. It is based on wavelet transform, particularly the multiresolution analysis (MRA) technique. The effectiveness of the proposed scheme was verified both in the experiment and in the field. Investigation results show that the scheme can detect the ground fault with high sensitivity and selectivity during all operating conditions.

Differential Protection Based on Zero-Sequence Voltages for Generator Stator Ground Fault

This paper introduces a new differential protection scheme based on zero-sequence voltages with 100% coverage for generator stator ground faults. Analysis shows that the Delta-fundamental zero-sequence voltages and the Delta-third-harmonic voltages at the generator neutral and the terminals will change simultaneously, and they present some similar characteristics. According to that, the new scheme that exploits the fault information of both the zero-sequence fundamental voltage and the third-harmonic voltage is described. As it combines the information of the zero-sequence fundamental voltage and the third-harmonic voltage, the scheme can detect the ground fault with high sensitivity in 100% coverage winding. Simulation and field test results show that the proposed scheme can obtain higher sensitivity than the traditional schemes

A New Weak Fault Component Reactance Distance Relay Based on Voltage Amplitude Comparison

A new weak fault component reactance distance relay is proposed in this paper. By adaptive setting of the compensated voltage, the scheme synthesizes the performance of the impedance distance relay and the reactance distance relay. The distance protection relay on the receiving end will misoperate when the fault resistance is larger than the critical resistance. So a new switching criterion is applied to eliminate this disadvantage. Based on that, the proposed scheme can detect the fault with the high fault resistance in the setting coverage, regardless of whether the relay is located at the receiving end or the sending end. Test results from the simulation and experimental conditions show that the new scheme is successful in detecting the internal fault. It has higher sensitivity and selectivity during different conditions than the traditional fault component protection schemes.

A Novel Differential Protection Scheme for the Generator

This paper presents a new scheme to distinguish the internal fault or the external fault based on phaselet algorithm. For the generator ratio restraint differential protection, the restraint current is decreased owing to CT saturation caused by the external fault, which always results in the maloperation. In order to enhance the operating characteristic of the protection, generator differential protection will select different restraint currents according to the different fault current characteristics. According to that, the method for choosing the corresponding restraint currents is then introduced. The simulation results show that the scheme can effectively prevent the generator differential protection from maloperation caused by CT saturation, and availably enhance the sensitivity of the differential protection during the internal fault.

New generator split-phase transverse differential protection based on wavelet transform

This paper presents a new split-phase transverse differential protection for a large generator based on wavelet transform. Research results show that there is almost no harmonic component on normal conditions, but it will produce great high-frequency current component when an internal fault occurs, which can be used to detect generator internal fault. With decomposition and reconstruction of the transient currents with wavelet transform, the high-frequency band fault currents are exploited in the new scheme. And the realization of the proposed protection device is also described in this paper, including the relay software and hardware design. The results from the experimental and field tests demonstrate that the new scheme is successful in detecting the generator internal fault. It has higher sensitivity and selectivity than the traditional protection scheme

Modeling and Simulation of MAS-based Management System for Smart Grid with Smart Homes

Traditional power system is undergoing revolutionary changes. Concepts like Smart Grid and Smart Home have come into practice due to high penetration of distributed generation and advanced information technologies. This paper incorporates Smart Home and Smart Grid. It focuses on a community where houses are equipped with photovoltaic panels, energy storage system and smart appliances. A new management system is proposed based on multi-agent technology. Agents are designed to be intelligence, autonomous and with high plug-and-play capability. System control architecture has three levels corresponding to management of devices, houses and community. A two-level operation optimization scheme is proposed, in which operation optimization problem is decomposed into five constrained multi-objective problems, mutual supply mechanism is deployed to efficiently coordinate Smart Homes and NSGA-II is introduced to obtain Pareto-optimal solutions. Simulation results validate the effectiveness of proposed management system.Traditional power system is undergoing revolutionary changes. Concepts like Smart Grid and Smart Home have come into practice due to high penetration of distributed generation and advanced information technologies. This paper incorporates Smart Home and Smart Grid. It focuses on a community where houses are equipped with photovoltaic panels, energy storage system and smart appliances. A new management system is proposed based on multi-agent technology. Agents are designed to be intelligence, autonomous and with high plug-and-play capability. System control architecture has three levels corresponding to management of devices, houses and community. A two-level operation optimization scheme is proposed, in which operation optimization problem is decomposed into five constrained multiobjective problems, mutual supply mechanism is deployed to efficiently coordinate Smart Homes and NSGA-II is introduced to obtain Pareto-optimal solutions. Simulation results validate the effectiveness of proposed management system.

A selection strategy for interconnection point of distributed generators

The technologies and application of distributed generators (DGs) are progressing rapidly due to the advantages of DGs. The penetration of renewable resources becomes higher and higher, which brings a lot of problems in distribution networks (DNs). The selection of interconnection point for DGs is required to be solved urgently. In this paper, the factors impacting on the interconnection includes host DN structure, DG characteristics, and DG function, which are analysed in order to provide the constraints for the selection strategy. The objective of the selection strategy is to search the interconnection point with the minimum equipment and operation costs. The IEEE 34-node test bed and a practical project of the building integrated photovoltaic in Shanghai are utilized to demonstrate the effectiveness of the selection strategy.