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1、英文译文译文：中性点非有效接地配电网故障选线新原理曾祥君 尹项根 陈德树 张哲(华中理工大学电力系, 武汉430074)摘要：提出采用负序电流及故障点损耗能量进行故障选线的新原理,该原理不受中性点接地方式的影响,适用于中性点不接地配电网、经消弧线圈接地配电网,甚至全补偿运行的配电网,该原理适合就地安装,便于在馈线就地控制终端单元(FTU) 上实现. 原理已经仿真分析及模拟实验论证。.关键词：继电保护 故障选线 配电网在中国，大多数配电网都是单独的系统或是中性点谐振接地系统。中性点非有效接地的配电网随着经济的发展在安全与电能方面提供了质量保证。不幸的是，配电网的故障接地支路很难检测。在独立单独的
2、电网系统中，故障接地支路的零序电流大小为其他支路流入的总和，而且故障接地支路的零序电流方向与非故障支路相反。因此，能通过比较故障支路和非故障支路零序电流的幅值或相位来进行故障接地支路的选线。然而，在谐振接地系统里，流经故障接地支路的电流很小。通过对消弧线圈的补偿电流，干扰了零序电流在故障和非故障线路的方向。因此，通过比较零序电流的幅值和相位很难进行故障线路的选线。另一方面，消弧线圈接有高电阻产生了高次谐波，因此消弧线圈完全不影响高次谐波电流。通过比较谐振接地系统的高次谐波零序电流的幅值与相位，能进行单相故障线路的选线。在高次谐波电流中,五次谐波电流分量最适合进行故障接地选线。很多人都认识到了这
3、一点。但是谐波电流非常的小而且在不同的系统中也使变化的。因此在实际中缺乏灵敏性。在欧洲，通过补偿装置（消弧线圈）并联电阻的特点增加了故障电流。所以，当发生单相方向接地故障或低电阻接地故障时，在保护系统中，由于残余电流的输入，增加了零序电压，这是一个很好的结果。然而，发生高电阻故障接地时，就不是这种情况。为了检测择高电阻接地故障支路，提出了一种新的选线方式，即比较零序电流的有功分量来选线。但是在电网中有功分量非常小。因此这种继电保护在实际中很难实现。本文中，基于在故障点负序电流的变化和能量的散发，提出了一种新的选线原理，这种原理不影响中性点接地系统方式。而且，它能适用于经消弧线圈接地故障和高电阻
4、接地故障。1.负序电流故障选线的原理与方法这部分介绍了基于负序电流故障选线的新方式。在谐振接地系统中，有n条支路，当第k条发生故障接地（如图.1）。 图1.电网故障接地假设系统的对称的，通过故障点的正序电流、负序电流、零序电流表示为： （1）这里为电网全阻抗零序电流；为阻抗正序电流；为阻抗负序电流；为故障电阻。 （2） 这里为支路i的负序阻抗（包括负载的零序阻抗）；为系统的负序阻抗。故障接地后负序电压为： （3） 支路i（非故障线路）的负序电流为： （4） 支路k（故障线路）的负序电流为： （5） 许多配电网是分布式的系统，各支路不和其他的系统连接。因此，任何一路负载的负序阻抗远远高与系统的。
5、所以： （6） 从公式（1）、（4）、（5）和（6），我们得出： （7）接地故障支路的负序电流等于三分之一的故障电流，远远大于有效支路的电流。因此，通过比较故障接地时所有之路的负序电流的振幅来实现故障接地支路的选择。系统和负载负序阻抗的感性参数时一样的，都是相电流滞后相电压。在负序电流中，感性分量是阻性分量的好多倍。图1中的负序向量图如图2： 图2.负序向量图 故障点的负序电流向量和故障相电压的向量是同方向的。而且故障接地支路的负序电流向量在方向上与故障相的电压相同。但是，有效支路的负序电流和故障相的电压在方向上的相位不同，电压相位超前。所以，故障接地支路也能通过比较负序电流向量的方向来选线。
6、如果要考虑负载的不平衡电流，在有效电网中存在着一些负序电流。为了消除负载不平衡电流的影响，负序电流的变化被用来选择故障接地支路。这里有四种方法去计算负序电流 ( n)的变化，通过计算机采集时间n 。 假设采样周期为T： (a)(b)(c)(d)为了减小负载波动的影响，上述方法经常被采用。因此，当零序电压超过了极限，表明故障接地发生了。这里有两种方法去检测选择故障支路。一种是比较各个支路的负序电流的变化和它的极限。如果某支路的负序电流的变化比较大，此支路便是故障支路。另一种方法是比较各个支路的负序电流的变化和故障相的电压。如果在方向相同，那便是故障支路。如果没有故障支路被发现，那么可能是母线保护
7、故障接地。在自动分配电网系统中，故障点要求被自动隔离。故障检测装置最好安装的位置是在馈线就地控制终端单元(FTU)。在配电网中，所有的故障检测都必须相互匹配。原文：New Principle for Grounding Fault Feeder Detectionin MV Distributions with Neutral Ineffectively EarthedZeng Xiangjun Yin Xianggen Chen Deshu Zhang Zhe(Department of Electrical Power Engineering , Huazhong University o
8、f Science and Technology , Wuhan 430074)Abstract :A new principle for grounding fault feeder detection based on negative sequence current variation and energy dissipated in the fault point is presented. It has high precision in both isolated systems and resonance earthed systems , even in f ull2comp
9、ensated systems. And it can be installed at the local control unit of feeder in distribution automation systems , such as field terminal unit ( FTU) . This principle is verified by EMTP simulator and experimentation.Key words : protective relaying , fault detection , distribution networksMost distri
10、bution networks are isolated systems or resonant earthed neutral systems China .These distributions with neutral ineffectively grounding can achieve significant and economical improvements in safety and power supply quality. Unfortunately , grounding fault feeder is difficult to be detected in these
11、 distributions 1 - 3 In isolated systems , the zero sequence current magnitude of grounding fault feeder is t he sum of other sound feeds , and the zero sequence current direction of grounding fault feeder is opposite to sound feeders . So the grounding fault feeder can be detected by comparing fund
12、amental zero sequence currents amplitudes or phases in t he isolated systems. However , in resonant earthed systems , grounding fault current is very small . The direction of fundamental zero sequence current is disturbed by t he compensation current due to Petersen-coil . So t hat , it is impossibl
13、e to detect the fault feeder by comparing fundamental zero sequence current s amplitudes and phases.On the other hand , Petersen-coil has high impedance to high order harmonics , so it has littleeffect to high order harmonic current . The grounding fault feeder can be detected by comparing harmonic
14、zero sequence current s amplitudes or phases of all feeders in resonant earthed systems. Among high order harmonic current s , t he fifth order harmonic current is t he best one to be used to detect the grounding fault feeder. Many utilities have realized it 4 . But the fifth order harmonic current
15、is very small and it varies in different systems , so it often has poor sensitivity in practice.In Europe , many utilities increase the fault current by adding a resistor parallel connection with compensation equipment (Petersen-coil) 3 . Therefore , when a single-phase directly grounding fault or a
16、 low resistance-grounding fault occurs , the wattmetric protection systems , which use the product of zero sequence voltage multiplied by residual current as input , has a good result. However , when high resistance grounding faults occur this is no longer the case3 . In order to detect high resista
17、nce grounding fault feeder , a new method is presented by comparing the active component of zero sequence current 3 . But the active component is very small in many distribution systems. This relay is also difficult to be realized in practice.In this paper , a new principle for grounding fault detec
18、tion based on negative sequence current variation and energy dissipated in the fault point is developed. This principle is not affected by the method of system neutral grounding. And it can be used in the detection of both arc grounding fault and high resistance grounding fault .1 The Principle and
19、Technique for Fault Detection by NegativeSequence CurrentA new method for grounding fault detection based on negative sequence current is presented in this section. A resonant earthed system , which has n feeders , get s grounding fault on the feeder k (see Fig.1) . It is supposed that the system is
20、 symmetrical . The positive sequence current , negative sequence current and zero sequence current through t he fault point can be derived. (1)where is the zero sequence impedance of the network ; is the positive sequence impedance ; is fault resistance ; is negative sequence impedance. (2) Fig. 1 G
21、rounding fault on an MV networkwhere is the negative sequence impedance of feeder i (include the negative sequence impedance of loads) ; is the negative sequence impedance of system (source) .The negative sequence voltage caused by grounding fault is: (3)The negative sequence current in the sound fe
22、eder i : (4)The negative sequence current in t he sound feeder k i : (5) Most distribution networks are radial systems in which the feeder is not connect with other source. So the loads negative sequence impedance of anyone s feeder is very higher than that of the source. Therefore : (6)From Eqs. (1
23、) (4) (5) and (6) , we can derive: (7)The negative sequence current of grounding fault feeder is about equal to one third of fault current , and it is much larger than that of sound feeder. So the grounding fault feeder can be selected by comparing the amplitude of negative sequence current s of all
24、 feeders which are caused by grounding fault 5 .The negative sequence impedance of source and that of loads have some characters of inductance , in which the phase of current lags that of voltage. And t he inductive component is several times of the resistive component in negative sequence current .
25、 The vectors diagram for negative sequence current in Fig. 1 is showed in Fig. 2. Fig. 2 Negative sequence vectors diagramThe negative sequence current vector of fault point has the same direction with the voltage vector of fault phase . And the negative sequence current vector of fault feeder is si
26、milar with the voltage vector of fault phase in direction. But the phase difference between the direction of sound feeders negative sequence current and t hat of fault phase voltage is greater than 90. So the grounding fault feeder can also be selected by comparing the direction of negative sequence
27、 currents vector.If the unbalance of load is considered , there are some negative sequence current exist in sound network. In order to clear up the effecting of load unbalance , the variation of negative sequence current is used to detect the grounding fault feeder. There are four methods to calcula
28、te the variation of negative sequence current ( n) in the sample time n by computer , supposed that the sample time is T in a foundational frequency cycle :(a)(b)(c)(d)In order to reduce the affection of load fluctuation , the method (d) is usually chosen. Therefore , while zero sequence voltage exc
29、eeds a threshold , grounding fault is happening. There are two ways to detect the fault feeder. One way is comparing the negative sequence current variation of each feeder to its threshold. If some feeders negative sequence current variation is bigger ; this feeder is t he fault feeder. The other wa
30、y is comparing the negative sequence current variation of each feeder to the voltage of fault phase. If there have similar direction , that feeder is the fault feeder. If there is no fault feeder to be detected , it may be the busbar grounding fault. In distribution automation systems , t he grounding fault point is asked to be isolated automatically. The best place for fault detector installing is field terminal unit ( FTU) . All fault detectors in a distribution system are asked to match each other in time-set.