Impact of six phase transmission line faults on turbine-generatorshaft torsional torques

This paper explores the impact of six-phase transmission line faults and their subsequent fault clearing and reclosing on the torsional torques induced in turbine-generator shafts. In this context, investigations have been conducted on a large turbine-generator unit connected to a sample power system. The paper presents also a comparison between the torsional stresses induced in the turbine-generator shafts during these events with their corresponding disturbances of a three-phase transmission system. The results of these investigations are presented in the form of typical time responses as well as parametric studies. The EMTP is used for the simulation studies. The studies conclude that six-phase transmission line faults generally induce torsional torques in the turbine-generator shaft whose magnitudes are relatively higher than those induced due to transmission line faults in a three-phase system. This conclusion is true for both sustained faults and faults followed by clearing and high-speed reclosing operations     

Six-phase (multiphase) power systems: Some aspects of modelling and fault analysis

This paper presents a further step in the mathematical modelling and analysis of six-phase (multiphase) systems. In earlier publications, a six-phase line, several three-phase/six-phase transformers, loads and a six-phase generator were modelled. The three-phase equivalent representations of various elements were obtained for analysis of the overall system on a three-phase basis. In this paper the equivalent six-phase representations of various elements of a composite three-phase/six-phase system are derived for investigating the phenomena on the six-phase side of the network. Utilizing the element models discussed in the paper, several alternative schemes for fault analysis of a six-phase system employing transformation as well as phase coordinate methods are developed. The validity and effectiveness of the proposed schemes are demonstrated with the help of a sample system.     

Six-phase (multiphase) power systems: Transient stability analysis

This paper addresses itself to the investigation of six-phase (multiphase) power systems which are currently being developed as potential alternatives to the conventional three-phase systems. Various aspects of six-phase systems, viz. feasibility, modelling, load flow and fault analysis, have already been examined. In this paper, the three-phase techniques of transient stability analysis are extended to six-phase systems. The equivalent single-phase as well as phase coordinate representations are employed to simulate the transient stability behaviour of six-phase systems. A sample system is worked out to illustrate the procedure and to focus on certain salient features of the performance of six-phase systems compared with that of conventional three-phase systems.     

Six-phase (multiphase) power transmission systems: A generalized investigation of the load flow problem

This paper deals with the generalized investigation of load flow problems of six-phase (multiphase) power transmission systems and presents several schemes for power flow calculations covering balanced and unbalanced network situations. Initially, the system models and algorithm for the assembly of the multi-phase bus admittance matrix are described. Equivalent single- and three-phase load flow studies are carried out employing the equivalent single- and three-phase representations of a six-phase transmission system. The procedure for phase coordinate load flow retaining the physical identities of the three-phase and six-phase elements is developed to investigate the problem of unbalances existing both in a three-phase and a six-phase portion of a composite power transmission network.The problem of obtaining effective starting solutions is also investigated and the computational requirements for various cases are quantified. The procedures developed in the paper are implemented on a sample system. Finally, the paper concludes with a discussion of the major findings and a future line of investigation.     

A general treatment of phase faults on a six-phase generator

One of the problems that must be thoroughly investigated from the operational point of view is the fault analysis of a multiphase power system. The variety of faults in a six-phase system is far more complicated than in a three-phase system. This paper presents three simple algebraic equations for sequence currents, actual fault currents and post-fault terminal voltages for the most general phase(s) fault on a six-phase generator. The sequence currents, when written in the format suggested, immediately indicate the method of connecting sequence networks for the simulation of faults on a network analyser. The connections of the sequence networks for some faults not discussed in the literature so far have also been given.     

Analysis of simultaneous ground and phase faults on a six phasepower system

An analysis is presented of any simultaneous sustained ground and phase fault. A single algebraic equation is presented for the calculation of sequence currents following a sustained simultaneous ground and phase fault at the terminals of a six-phase generator. The equation can be simulated on a digital computer or a network analyzer for the simulation of any type of fault. The connection of sequence networks is at once indicated when the sequence currents are written in the format suggested. The variety of faults on a six-phase system is far more complicated than on a three-phase system. The generalized treatment of all faults will prove useful in evolving protective relaying schemes for six-phase power systems     

三相-六相混合输电系统分析的和差分量法

三相-六相混合电力系统已有20多年的运行历史,由于六相输电系统结构相对复杂,为系统分析、计算带来了不同于三相系统中的许多新问题,现有的对这种混合输电系统的计算方法繁琐复杂.在对此进行深入研究和探讨的基础上,提出了一种将六相电压、电流变换为三相电压、电流的计算方法,借助于此方法,可将六相系统简化为三相系统,从而可将三相-六相混合输电系统的分析转化为三相电力系统的分析,还特别研究了六相系统中的线路阻抗,三相-六相变压器的三相等效原理.     

Fault analysis of six-phase systems

This paper presents an overview of the feasibility of six-phase transmission, symmetrical and Clarke's component transformations for six-phase systems derived from firm group theoretic considerations, and an analysis of the various faults likely to occur on six-phase systems. A numerical example is given to compare the magnitudes of fault currents involved for a six-phase and a double-circuit three-phase system for the most severe and most common cases. Finally, the future scope of the present investigations is indicated.     

Microprocessor-based negative-sequence relay

A three-phase power system can be subjected to various types of faults. Symmetrical components furnish a tool which is well suited for analysing such faults. This paper describes a microprocessor-based system which calculates the symmetrical components from the sampled data of the three phase quantities in real time. The computed symmetrical components can be used conveniently in a variety of protection schemes. A negative-sequence relay for the protection of three-phase generators is described. The relay protects a generator against negative-sequence current using a constant-current extension of the characteristic of an inverse-time induction relay responsive to negative-sequence current. The performance of the relay has been evaluated in the laboratory under various fault conditions. Some test results are included in this paper.     

基于S函数的数字式变压器差动保护仿真

利用Matlab中的Simulink及SPS(SimPowerSystem)工具箱建立变压器仿真模型,利用S函数(S-Function)进行差动保护算法编程,以实现差动保护功能,建立了双绕组变压器差动保护的仿真模型,其中包括了比率制动与二次谐波制动等模型。在仿真模型中,该差动保护功能可以反应变压器差动保护区内的不同类型的故障,并能正确动作于跳闸;当空载投入变压器时,该差动保护又能够根据励磁涌流可靠闭锁。仿真结果表明,S函数所编写的数字式差动保护的S函数仿真程序是正确的。还对部分S函数(S-Function)编写的差动保护算法语句进行了说明。     

Evaluation of twelve-phase (multiphase) transmission line parameters

Multiphase transmission is proving to be the most promising alternative to conventional three-phase power transmission in offering advantages which could meet many of the needs that have developed for overhead transmission in recent years. Several investigations have presented different aspects of this new power transmission technology. However, information regarding the line parameters is not available in adequate detail. This paper is concerned with the analytical development and evaluation of line parameters of a twelve-phase system, inductance and capacitance matrices, matrix diagonalizing transformation, modes of propagation and a line parameter model for system simulation and transient studies. The paper contains illustrative calculations to validate the expressions derived and also to give a comparative view of twelve-phase parameters with their six-phase and three-phase counterparts.     

六相电力系统的故障计算方法

介绍了一种基于模态的六相电力系统的故障计算方法,利用六相系统的对称性,通过对阻抗阵进行变形,使其解耦成两组三相系统,并分别对这两组三相系统采用不对称故障的分析方法,将其组成六相系统的复合序网,以此对其进行不对称短路故障的计算。     

220kV甘棠变一起电网事故的处理与分析

针对甘棠变一起由雷击造成110kV线路三相近区故障、综自系统异常、田甘线202开关及白甘线201开关三跳事故,从继电保护原理、保护动作、直流系统故障和逆变电源异常等方面进行了分析;总结了暴露的问题,提出了解决办法和改进措施。     

Double Three-phase Induction Machine Modeling for Internal Faults Simulation

Multi-phase induction motors present excellent characteristics for faulty tolerant operation. Among them, six-phase induction motors, which are among the most used, exhibit two types of configuration: the double three-phase and the six-phase with single neutral. The double three-phase presents the advantage of reducing harmonics with its symmetric winding. This article presents a new modeling of the double three-phase induction machine for internal faults simulation. The developed model is composed by two sets of three-phase stator windings forming two stars. The model considers an arbitrary displacement (α) between stator stars, allowing the simulation of this type induction machines with different configurations, with 60° displacement used herein. The simulations of internal faults, such as stator windings or rotor faults, are both considered in the proposed model, allowing the machine study under abnormal conditions. The double three-phase induction machine model was fully implemented in real coordinates, making it possible to simulate stator and rotor faults without being necessary to change system equations coordinate. Several examples allow verifying the characteristics of the proposed model and its application for internal fault analysis. Experimental results are also presented to validate the obtained simulation results.     

Analysis of multiphase induction machines with winding faults

The paper shows how the techniques of generalized harmonic analysis may be used to simulate the steady-state behavior of a multiphase cage induction motor with any form of open-circuit or short-circuit fault in the stator winding. The analytical model is verified using a four-pole machine with a 48-slot stator. Each coil of the stator winding of this machine is brought out to a patchboard that enables the stator to be configured for single-phase, two-phase, three-phase, four-phase, six-phase, or 12-phase excitation. Experimental results are compared with computer predictions for a six-phase machine with both open-circuit and short-circuit faults.     

Induction motor transient response to multiple faults in unbalanced power systems

Although the effects of an unbalanced supply on overheating induction motors have been known for some time, little or no attention has been paid to the dynamic response of such a system. A recent investigation though has evaluated the effects of an unbalanced distribution system, unbalanced single-phase loads, unbalanced shunt faults, and series faults (open conductor) on the transient behavior of a three-phase induction motor. This paper extends that work to the case of motor transient response due to multiple asymmetrical faults in an unbalanced power system. The paper investigates the dynamic behavior of an induction motor connected to an unbalanced three-phase power system subjected to a shunt fault at one location and blown fuses or open conductor at another location. The method involves phase frame representation of the line. A significant finding is that certain multiple faults cause the induction motor to lose stability.     

适用于柔性直流互联交流系统的无电压方向元件判据

背靠背柔性环网控制装置的应用使配电网由单端电源供电的辐射状网络变为多端电源供电网络,三段式电流保护无法判断故障方向。为了既保证配电网保护动作可靠性又保留三段式电流保护,需要为保护安装方向元件。文中通过研究背靠背柔性环网控制装置接入的交流配电网发生不同位置相间故障时序电流间的相位规律,提出了基于流过保护的负序电流和同一母线上无源支路正序电流间相位关系的故障方向判别元件,并给出了正反方向故障时方向元件的动作区间。该方向元件适用于由传统电源、采用负序电流抑制的柔性环网控制装置或分布式电源构成的且母线含无源支路的多端供电网络。该元件受过渡电阻影响小,无需安装电压互感器,在三相对称故障时仍可保证保护的正确动作,不存在传统功率方向元件出口三相故障时的死区问题。经PSCAD仿真验证了该方向元件在系统不同位置发生各种相间故障时的正确性和有效性。     

Transmission line individual phase impedance and related pilot protection

This paper proposes a kind of new Individual Phase Impedance (IPI) and a novel pilot protection scheme for transmission line based on the IPI. The IPI is calculated by the ratio of the voltage difference of fault-superimposed component to the current difference of fault-superimposed component at both terminals of the protected line. The IPI has accurate mathematical expressions and reasonable physical definitions for various line models. The calculated result of IPI can be used to distinguish the internal faults from the external faults. When the IPI is identical to the value of line positive-sequence impedance, the external fault is detected; otherwise, the internal fault is detected if it differs from that value. The feature of the pilot protection scheme is that the inter-phase coupling relation and the distributed capacitance based on the three-phase line model are directly considered and included in the IPI expression. The novel pilot protection can be used for long distance HV transmission lines with some preeminent performances which are deficiency in the conventional directional comparison pilot protection and current differential protection. The test results obtained by EMTP simulation and from a laboratory model of a simplified real power system have demonstrated that the pilot protection is of high reliability and good adaptability.     

白鹤滩-江苏特高压混合直流输电线路行波保护适应性分析

为探究现有直流输电线路行波保护对白鹤滩-江苏特高压混合直流输电系统(简称：白江混合系统)的适应性,根据白江混合系统直流线路故障附加网络推导直流线路区内外故障时线路两端故障行波的边界传播特性。分析发现,直流线路正向区外故障后边界传播特性与传统直流系统存在差异。进一步分析行波保护判据的变化情况,表明行波保护判据主要受整流侧反射系数和逆变侧折射系数的影响。将白江混合系统与传统直流输电系统进行对比,发现当直流输电线路正向区外发生短路故障后,白江混合系统电压变化量、电压变化率、极波变化量和极波变化率比传统直流系统变化更大,导致行波保护误动风险增大。最后,基于PSCAD搭建白江混合系统仿真模型,仿真结果验证了理论分析的正确性。