Series faults in six-phase electric poer systems

The planning and design of transmission systems require the analysis of systems under steady-state as well as under transient conditions.This paper addresses a group of medium-fast transients in six-phase systems created by faults which do not involve any connection between conductors or between conductors and ground. This type of imbalance is referred to as a series fault; it arises, in most instances, when poles of a circuit breaker fail to open, thus creating an unbalanced series impedance condition. The various cases of series faults or open-line faults for six-phase transmission systems are analyzed in this work using the method of symmetrical components and Thévenin's theorem for two-port networks. A numerical algorithm for each of the various series fault cases is also developed here. This will allow us to determine the unbalanced currents resulting from an unbalanced series impedance condition.     

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.     

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。     

Transient performance analysis of a six-phase pole change induction motor for electric vehicles

We previously proposed a six-phase pole change induction motor (six-phase PCIM) for electric vehicles (EVs), and have presented its operating principle and steady state characteristics. The six-phase PCIM expands the constant power operation range using the pole change technique without mechanical contactors; therefore it possesses superb characteristics for miniaturizing EV driving systems. This paper proposes a new analysis method for the six-phase PCIM in order to derive basic equations which can be used to analyze transient phenomena caused by pole change and to create control methods. First, a “six-phase tensor-transformed rotational d-q axis” is defined and its physical meaning made clear. By using this axis, voltage and torque equations which can uniformly deal with the steady state and transient states will be derived. Next, we compare measured and simulated results of voltage, current, and torque characteristics in steady state and in transient states at the pole change operation and both-pole dual operation. Through these comparisons, the validity of our theory and its effectiveness to performance analysis and application to the control method for the six-phase PCIM is discussed in detail. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 59–71, 1997     

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.     

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     

三电平六相同步电机变频调速技术研究

中压逆变技术是大容量变频调速的首选方案,但受到功率器件耐压等级和导通电流的限制,仅仅依靠中压逆变技术来进一步提升调速系统的容量已经变得非常困难。多相电机是实现大容量传动的又一途径。该文以这两种技术为研究背景,探索结合中压逆变技术和多相电机技术的调速方案：文章在三相同步电机矢量控制的基础上扩展建立了六相同步电机的气隙磁通定向矢量控制方法和六相同步电机的气隙磁链观测技术;文章将六相逆变器分解为两个三相逆变器来控制,从而简化了六相三电平逆变器的空间矢量调制和中点电位平衡处理。作者利用这些技术设计开发了"690V/ 200kW三电平六相同步电机变频调速装置",并在该装置上进行大量动态和稳态实验研究,取得良好的运行效果。     

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.     

Relay protection operation for faults on Nyseg's six-phasetransmission line

This paper describes the performance of the protection system used for the first commercially operated six-phase transmission line in the world-New York State Electric & Gas's 93 kV (phase to phase and phase to ground) line from Goudey Station to Oakdale substation (USA) during faults in the winter of 1993. The paper briefly describes the basics of the High-Phase Order Transmission Demonstration Project and the integration of available state of the art microprocessor based relays, with a programmable logic relay (designed for the protection of conventional three-phase systems) in a hierarchical six-phase protection system. The operation of the protection system during two faults on the line in January and February 1993 is reported. The modeling of the six-phase line in a conventional three-phase short circuit study program is also considered and a comparison between the measured and calculated fault currents is presented     

超高压六相交流输电线路稳态运行特性分析

六相交流输电线路对称性好,在多相输电线路中具有独特的优势。六相输电线路稳态运行特性的分析是研究六相输电的一项重要内容。本文分析了空载情况下六相输电过电压的计算方法,建立了六相交流输电系统仿真模型,并给出了空载、轻载、匹配、重载及终端短路故障几种情况下的稳态运行分析结果。     

基于六序分量法的六相输电系统故障选相

六相输电是多相输电技术中最接近实用化的一种.针对其多达120种的故障,运用同正、负、零序和反正、负、零序的六序分量法分析六相系统故障,变换得到的各序分量物理含义清晰.六相系统中的同序量、反序量分别对应于双回线中的反序量、同序量,依据故障边界条件构成的复合序网得到了六相系统的序分量特征以及与六相系统兼容运行的三相系统序分量特征.在此基础上,提出一种判别六相输电系统故障类型的方法,可用作六相输电线路的选相元件动作判据.     

六相三电平并网逆变器及其控制方法

针对中性点钳位型三电平并网逆变器(NPC,Neutral Point Clamped Inverter)存在的中点电位不平衡问题,设计了一种六相三电平并网逆变器,并对其主电路结构和控制方法开展研究。首先,通过对主电路结构进行分析,阐述了六相三电平逆变器的工作原理,分析可知六相三电平逆变器不使用续流二极管和分压电容,从而避免了中点电位不平衡问题;其次,对六相三电平逆变器的控制方法进行研究,提出六相三电平逆变器的SVPWM(Space Vector Pulse Width Modulation)控制方法;进而,用MALTAB/Simulink软件对其进行仿真,并与NPC型并网逆变器进行对比分析;最后,通过1 k W的实物模型实验,验证了方案的可行性。     

A six-phase series-connected two-motor drive with decoupled dynamic control

This paper analyzes a six-phase two-motor drive, consisting of a six-phase voltage-source inverter (VSI), a six-phase induction machine, and a three-phase induction machine. Stator windings of the two machines are connected in series in an appropriate manner. This enables full decoupling of the dynamics of the two machines by means of vector control. Detailed mathematical modeling of the system is performed and the set of d-q equations, describing the two machines connected in series to a six-phase VSI, is developed. The resulting model clearly shows the possibility of independent vector control of the two machines, although a single VSI is used as the supply. An experimental rig is constructed and existence of the decoupled dynamic control of the two machines supplied from a single VSI is fully verified by extensive experimental testing.     

Basic principle and maximum torque characteristics of a six-phase pole change induction motor for electric vehicles

In addition to basic characteristics such as small size, lightweight and easy maintenance, the electric vehicle (EV) motor is required to possess characteristics that allow for the production of high torque in low-speed region and to realize a wide-speed range of constant power in high-speed region. In an attempt to improve further the constant power operation of the induction motor (IM), this paper proposes a six-phase pole change IM (six-phase PCIM). The six-phase PCIM further expands the constant power operation range without increasing either volume or current of IM. To clarify the basic principle and torque characteristics of the six-phase PCIM, its winding method and distribution of magnetomotive force (mmf) will first be examined. Then, by establishing a performance calculation method based on a quasisinusoidal wave method, the feasibility of a highly precise performance calculation sufficient for actual use will be demonstrated. Furthermore, by clarifying through experiment the maximum torque characteristics, the feasibility of expansion of the constant power operation range will be confirmed and its effectiveness in the EV will be discussed. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 78–91, 1997     

Generalized 12<Emphasis Type="Italic">n</Emphasis>-phase converter

Topological features and calculation relationships are considered for a 12n-phase converter with a multistage configuration of six-phase asymmetric voltage systems of secondary transformer windings. An example of a synthesized circuit of the phase number and shift converter is given for a 24-pulse rectifier recommended for use in networks with distorting factors.     

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.     

Design and Control Techniques for Extending High Frequency Operation of a CSI Induction Motor Drive

An investigation of the maximum speed capability of a current source inverter (CSI) drive in both a three-and a six-phase connection is presented. It is shown that a six-phase configuration has distinct advantages over a three-phase connection in high speed capability for the same peak motor spike voltages. In addition, with proper control of the firing pulses fed to the inverters supplying the six-phase machine, the speed range can be substantially extended beyond the maximum limit predicted using conventional control. Predicted analytical results are correlated with results obtained by a detailed hybrid computer simulation.     

特高压六相输电线路工频电场强度计算

为研究特高压六相输电线路表面电场和空间电场的特性,参考特高压同塔双回输电线路杆塔结构,计算设计特高压六相输电系统杆塔典型尺寸并选取分裂导线型号。在此基础上,考虑分裂导线中各子导线间的相互影响,计算特高压六相输电导线表面最大场强和线路下距地面1 m处的空间电场分布,并将计算值与相应电压等级的同塔双回线路进行比较,结果表明特高压六相输电导线表面场强和线路下距地面1 m处的空间电场均优于同塔双回线路。故特高压六相输电线路具有更好的环保性能。