输电线路的距离保护中英文翻译(共15页).doc

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1、精选优质文档-倾情为你奉上输电线路的距离保护在过电流保护灵敏度低或选择性差时，应当考虑采用距离保护。距离保护通常用于输电线路相间短路的主保护和后备保护，装有快速自动重合闸的线路不需要保持稳定性，而且在线路末端区域短路时容许短时间延时。过电流保护通常用于接地短路的主保护和后备保护，但接地故障也逐渐有运用距离保护的趋势。 单段式距离保护被用于发电机出线端相间短路的后备保护，同时，单段距离保护也可方便的用于电力变压器故障的后备保护。但在目前，还是用反时限过电流保护作为电力变压器故障的后备保护。 距离保护比电流保护更好，因为距离保护受短路电流大小变化的影响比电流保护小的多，因此，距离保护受电力系统运行

2、方式的影响非常小。这是因为，距离保护的继电器动作是依据阻抗而不是电流。 一、 全阻抗继电器、电抗继电器和电阻继电器的选择因为接地电阻是可变的，而接地距离继电器必须几乎不受短路电阻大的变化的影响。因此，电抗保护更适用于接地保护。对于相间保护，每一种类型都有它的优点和缺点。在非常短的线路段，使用电抗型继电器更好的原因在于它可以迅速的保护更长的线路。这是因为电抗继电器实际上不受过渡电阻的影响，这或许是与线路全阻抗继电器最大的区别。另一方面，在系统中产生严重的同步振荡时，电抗型距离保护在系统中的某个区域很可能发生误动作，除非提供额外的保护装置防止这种情况发生。电阻型继电器最适合用于可能发生严重的同步震

3、荡的长线路的相间短路保护。它可以不需要装设额外的保护设备防止线路发生同步振荡时发生误动作。当电阻型保护适合保护任何给定的线路段时，它的动作特性曲线在R-X图表中的区域最小，这意味着它受其他异常系统情况的影响比受线路故障的影响小；换句话说，在所有的距离保护中它最具有选择性。因为电阻继电器受过渡电阻的影响比其他类型的大，所以它适用于长线路。实际上它与方向继电器和测量阻抗继电器联合使用时将使它可靠性更好。全阻抗继电器能较好的实用于中等长度线路的相间短路保护，而不实用于太长或太短线路的保护。过渡电阻对全阻抗继电器的影响比对电抗继电器的影响大，而比对电阻继电器的影响小；系统同步振荡对全阻抗继电器的影响比

4、对电抗继电器的影响小，而比对电阻继电器的影响大。如果一个阻抗继电器的特性被补偿，可以使它成为一个改良的继电器，既可以类似于电抗继电器的特性也可以类似于电阻继电器的特性，但它总是需要一个独立的方向元件。各种类型的距离继电器在它们最适用的线路长度范围上没有严格的划分，实际上，这些区域存在着许多重叠。同样，系统中发生的变化，比如线路接线端的增加，可能要改换一种更实用于这种特殊区域的继电器类型。因此，应该了解距离保护所有的性能，选用最适合各自需要的继电器类型。在某些情况下在同一类型的保护中能获得更好的选择，除此之外，如果保护被用在最适合的各条线路上，相邻线路上的不同类型的保护在选择上没有明显的不利的影

5、响。二、距离保护的整定相间距离保护依据保护安装位置到短路位置之间线路的正序阻抗对给定的继电器进行阻抗整定，发生在这个范围外的短路继电器不动作。接地距离保护用同样的方法进行整定，尽管某些保护可以对零序阻抗作出反应。整定的这个阻抗，或者是它相应的距离，称为继电器或元件的保护范围。为了近视接近目的，习惯上取定一个正序阻抗平均值为每英里0.8欧姆的值作为户外输电线路架设的保护范围，并且可以忽略电抗。精确的数据在电力系统分析书中是可以找到的。在整定相间或接地阻抗继电器使初级阻抗转化为使用的二次阻抗时，可以使用下面公式 ： 式中 CT ratio是高压相电流与继电器相电流的比值，VT ratio是高压相电

6、压与继电器总相电压在三相平衡条件下的比值。例如，对于一条50英里长、输电电压为138KV的线路配置变比为600/5、Y型连接的 CT时，二次的正序阻抗值为：在实际中常整定距离保护第I段的保护范围为双端线路长度的80%90%，或为多端网络中最近两端距离的80%90%。这一段保护区内没有时间延迟。距离保护第II段保护的主要任务是保护第段保护元件保护范围外的线路。它的整定值应该可以使继电器在线路末端甚至发生经过渡电阻短路时能动作。为了实现这个目的，第II段保护的保护范围应延伸到线路末端以外。即使过渡电阻的影响没有被考虑，也应该把由于分支电流源的影响和由于（1）整定依据的数据，（2）电流和电压互感器和

7、（3）继电器产生误差的可能趋势考虑在内。通常第II段的保护区应至少达到相邻线路段的20；延伸到相邻线路的范围越大，用这个II段保护元件选择的在下一级线路III段保护区内能被允许的误差越多。图表 1 第二段保护元件正常选择的整定第II段保护范围的最大值也有一个限制，在第II段保护范围延伸的过远的情况下，最短的相邻线段上的距离保护的第二段保护元件选择的第II段保护范围足够小，如插图一所示的那样。瞬时过保护现象不需要考虑继电器有较高的复位率，因为造成过保护的瞬时现象将在第二段保护跳闸之前终止。然而，如果复位的比率低，第二段保护区必须设置( 1 )足够短的保护范围，这样其过保护将不超出相同的条件下的相

8、邻线段的第一段保护区的范围外，或者( 2 )有足够长的时间延迟作为相邻线路段的第二段保护区动作时间的选择，正如图2所示的那样。 在这种情况下，相邻线路上的继电器的任何欠保护的趋势必须被考虑。 如果一条相邻线非常图表 2 相邻线路保护第二段的延时特性短，以至于不可能得到继电器作出反应的需要的时间的选择，这时增加时间延迟是必要的，正如插图2.中所示那样。另外，第二保护区时间延迟应足够的长以保证 ( 1 ) 在线路的另一端的母线上的母线横差保护，(2) 在线路的另一端的母线上的变压器的变压器横差保护，或（3）相邻线路的线路保护最低的选择性。这些各种各样原理的断路器切断电路的时间也将影响第二段的动作时

9、间。这个第二段的动作时间通常大约为0.2秒到0.5秒。图表 3 第三段保护元件的正常整定特性第III段保护作为相邻线路的后备保护，它应尽可能的保护到最长相邻线路的末端外，在最大的保护范围内，图3是一个标准的后备保护特性图。第三段的动作延时通常大约为0.4秒到1.0秒。为了保护到长的相邻线路的末端仍然用短线路的保护来选择动作时间，它可能需要用额外的延时来达到选择性，如图4所示那样。图表 4 相邻线路第三段的延时整定三、过渡电阻对距离继电器动作的影响过渡电阻的区域在线路上是很小的一点，但在这个区域上距离继电器的动作将会从无时限延迟为第二段动作时间，或从第二段动作时间延迟为后备保护时间。我们考虑在无

10、时限区内的电弧使继电器在第二时间内动作，在第二段动作区的电弧使继电器在后备保护时间内动作，或在后备保护区的电弧阻止继电器彻底动作。换句话说，电弧的影响可能造成距离继电器的拒动。对于恰好在第一段保护区末的电弧，我们关心的是它的初始特性。距离继电器第一段区动作是那样快速，以至于，如果在这种情况阻抗遭电弧袭击时，保护区将会在电弧略微伸展进而增加其阻抗之前动作。 因此，我们可以计算弧的初始特性以确定相间短路导线间的最长等效距离，或相地短路绝缘子串的距离。另一方面，对于在第二动作时间或后备保护区的电弧，应该考虑电弧辐射的影响，再者，继电器整定的动作时间在结果上也是一个重要的方面。 当它在第二段或后备保护

11、区时，在较长的时间内电弧不得不在空气中辐射，实际上也是这样的，电弧故障离继电器越远，继电器的动作受的影响越小，也就是说，在继电器与故障点的线路阻抗越大，电弧阻抗增大时总的阻抗变化越小。另一方面，电弧离继电器越远，它表现出的阻抗越大，因为来自线路末端继电器的电流将变的更小，在下文将予以讨论。由于电弧的影响，无时限保护区的保护范围将略有减小，如果是不可避免的，它可以被容许。我们可以用电抗型或改良阻抗型距离继电器将这个缩小减到最小程度。第二段保护区的保护范围不是一定由于电弧而减小，但在电弧点下一级线路后的保护将不能被选择；当然，它们也受电弧的影响，但影响不是很大。电抗型或改良阻抗型距离继电器在使第二

12、段保护区保护范围的缩小程度最小方面也是非常有用的。插图5显示了阻抗或电阻特性如何被补偿使它图表 5 偏置继电器的特性使电弧影响最小对电弧的反应最小化。它也能通过使第二段保护区尽可能延伸来促进这种情况，以便在电弧的影响下容许一个特定的保护范围。一般的保护不在后备保护区使用电抗元件，而是使用全阻抗元件或电阻元件。如果电弧幅射太长，后备保护元件动作失败，可以使用改进的阻抗元件，电阻元件或起动元件的特性可以被改进使它的动作受过渡电阻的影响减小。一些类型的距离继电器稍微的重新设定它的特性在防止电弧辐射太长方面是很有利的。 尽管电弧本身实际上都是电阻，但从装设保护的线路末端看它可以有一个容抗或感抗。电弧的

13、电抗用下式来计算：式中：I1为从被保护线路末端流入电弧的电流， I2为从线路另一端流入电弧的电流， RA为电流（I1+I2）流过的电弧电阻。大量重要的实践表明，正如上面的公式所示那样，电弧阻抗的表现值比它实际的大，而且它的值可能非常高。当到达线路的另一端后，电弧阻抗值将非常的高，因为电弧电流将降低。然而，它的出现对于保护的影响将不会再扩大，因为电流I2将变为零。电弧的电阻对保护的影响是否比原来高还是低依赖于距离断路器断开前和后电流的相对变化关系和实际值。专心-专注-专业附录 5 LINE PROTECTION WITH DISTANCE RELADistance relaying should

14、 be considered when overcurrent relaying is too slow or is not selective. Distance relays are generally used for phase-fault primary and back-up protection on subtransmission lines, and on transmission lines where high-speed automatic reclosing is not necessary to maintain stability and where the sh

15、ort time delay for end-zone faults can be tolerated. Overcurrent relays have been used generally for ground-fault primary and back-up protection, but there is a growing trend toward distance relays for ground faults also.Single-step distance relays are used for phase-fault back-up protection at the

16、terminals of generators. Also, single-step distance relays might be used with advantage for back-up protection at power-transformer tanks, but at the present such protection is generally provided by inverse-time overcurrent relays.Distance relays are preferred to overcurrent relays because they are

17、not nearly so much affected by changes in short-circuit-current magnitude as overcurrent relays are, and , hence , are much less affected by changes in generating capacity and in system configuration. This is because, distance relays achieve selectivity on the basis of impedance rather than current.

18、THE CHOICE BETWEEN IMPEDANCE, REACTANCE, OR MHOBecause ground resistance can be so variable, a ground distance relay must be practically unaffected by large variations in fault resistance. Consequently, reactance relays are generally preferred for ground relaying.For phase-fault relaying, each type

19、has certain advantages and disadvantages. For very short line sections, the reactance type is preferred for the reason that more of the line can be protected at high speed. This is because the reactance relay is practically unaffected by arc resistance which may be large compared with the line imped

20、ance, as described elsewhere in this chapter. On the other hand, reactance-type distance relays at certain locations in a system are the most likely to operate undesirably on severe synchronizing-power surges unless additional relay equipment is provided to prevent such operation.The mho type is bes

21、t suited for phase-fault relaying for longer lines, and particularly where severe synchronizing-power surges may occur. It is the least likely to require additional equipment to prevent tripping on synchronizing-power surges. When mho relaying is adjusted to protect any given line section, its opera

22、ting characteristic encloses the least space on the R-X diagram, which means that it will be least affected by abnormal system conditions other than line faults; in other words, it is the most selective of all distance relays. Because the mho relay is affected by arc resistance more than any other t

23、ype, it is applied to longer lines. The fact that it combines both the directional and the distance-measuring functions in one unit with one contact makes it very reliable.The impedance relay is better suited for phase-fault relaying for lines of moderate length than for either very short or very lo

24、ng lines. Arcs affect an impedance relay more than a reactance relay but less than a mho relay. Synchronizing-power surges affect an impedance relay less than a reactance relay but more than a mho relay. If an impedance-relay characteristic is offset, so as to make it a modified relay, it can be mad

25、e to resemble either a reactance relay or a mho relay but it will always require a separate directional unit.There is no sharp dividing line between areas of application where one or another type of distance relay is best suited. Actually, there is much overlapping of these areas. Also, changes that

26、 are made in systems, such as the addition of terminals to a line, can change the type of relay best suited to a particular location. Consequently, to realize the fullest capabilities of distance relaying, one should use the type best suited for each application. In some cases much better selectivit

27、y can be obtained between relays of the same type, but, if relays are used that are best suited to each line, different types on adjacent lines have no appreciable adverse effect on selectivity.THE ADJUSTMENT OF DISTANCE RELAYSPhase distance relays are adjusted on the basis of the positive-phase-seq

28、uence impedance between the relay location and the fault location beyond which operation of a given relay unit should stop. Ground distance relays are adjusted in the same way, although some types may respond to the zero-phase-sequence impedance. This impedance, or the corresponding distance, is cal

29、led the reach of the relay or unit. For purposes of rough approximation, it is customary to assume an average positive-phase-sequence-reactance value of about 0.8 ohm per mile for open transmission-line construction, and to neglect resistance. Accurate data are available in textbooks devoted to powe

30、r-system analysis.To convert primary impedance to a secondary value for use in adjusting a phase or ground distance relay, the following formula is used:where the CT ratio is the ratio of the high-voltage phase current to the relay phase current, and the VT ratio is the ratio of the high-voltage pha

31、se-to-phase voltage to the relay phase-to-phase voltageall under balanced three-phase conditions. Thus, for a 50-mile, 138-kv line with 600/5 wye-connected CTs, the secondary positive-phase-sequence reactance is about It is the practice to adjust the first, or high-speed, zone of distance relays to

32、reach to 80% to 90% of the length of a two-ended line or to 80% to 90% of the distance to the nearest terminal of a multiterminal line. There is no time-delay adjustment for this unit.The principal purpose of the second-zone unit of a distance relay is to provide protection for the rest of the line

33、beyond the reach of the first-zone unit. It should be adjusted so that it will be able to operate even for arcing faults at the end of the line. To do this, the unit must reach beyond the end of the line. Even if arcing faults did not have to be considered, one would have to take into account an und

34、erreaching tendency because of the effect of intermediate current sources, and of errors in: (1) the data on which adjustments are based, (2) the current and voltage transformers, and (3) the relays. It is customary to try to have the second-zone unit reach to at least 20% of an adjoining line secti

35、on; the farther this can be extended into the adjoining line section, the more leeway is allowed in the reach of the third-zone unit of the next line-section back that must be selective with this second-zone unit.The maximum value of the second-zone reach also has a limit. Under conditions ofmaximum

36、 overreach, the second-zone reach should be short enough to be selective with the second-zone units of distance relays on the shortest adjoining line sections, as illustrated in Fig. 1. Transient overreach need not be considered with relays having a high ratio of reset to pickup because the transien

37、t that causes overreach will have expired before the second-zone tripping time. However, if the ratio of reset to pickup is low, the second-zone unit must be set either (1) with a reach short enough so that its overreach will not extend beyond the reach of the first-zone unit of the adjoining line s

38、ection under the same conditions, or (2) with a time delay long enough to be selective with the second-zone time of the adjoining section, as shown in Fig. 2. In this connection, any underreaching tendencies of the relays on the adjoining line sections must be taken into account. When an adjoining l

39、ine is so short that it is impossible to get the required selectivity on the basis of react, it becomes necessary to increase the time delay, as illustrated in Fig. 2. Otherwise, the time delay of the second-zone unit should be long enough to provide selectivity with the slowest of (1) bus-different

40、ial relays of the bus at the other end of the line(2)transformer-differential relays of transformers on the bus at the other end of the line,or (3) line relays of adjoining line sections. The interrupting time of the circuit breakers of these various elements will also affect the second-zone time. T

41、his second-zone time is normally about 0.2 second to 0.5 second.The third-zone unit provides back-up protection for faults in adjoining line sections. So far as possible, its reach should extend beyond the end of the longest adjoining line section under the conditions that cause the maximum amount o

42、f underreach, namely, arcs and intermediate current sources. Figure 3 shows a normal back-up characteristic. The third-zone time delay is usually about 0.4 second to 1.0 second. To reach beyond the end of a long adjoining line andstill be selective with the relays of a short line, it may be necessar

43、y to get this selectivity with additional time delay, as in Fig. 4.THE EFFECT OF ARCS ON DISTANCE-RELAY OPERATION The critical arc location is just short of the point on a line at which a distance relays operation changes from high-speed to intermediate time or from intermediate time to back-up time

44、. We are concerned with the possibility that an arc within the high-speed zone will make the relay operate in intermediate time, that an arc within the intermediate zone will make the relay operate in back-up time, or that an arc within the back-up zone will prevent relay operation completely. In ot

45、her words, the effect of an arc may be to cause a distance relay to underreach.For an arc just short of the end of the first- or high-speed zone, it is the initial characteristic of the arc that concerns us. A distance relays first-zone unit is so fast that, if the impedance is such that the unit ca

46、n operate immediately when the arc is struck, it will do so before the arc can stretch appreciably and thereby increase its resistance. Therefore, we can calculate the arc characteristic for a length equal to the distance between conductors for phase-to-phase faults, or across an insulator string fo

47、r phase-to-ground faults. On the other hand, for arcs in the intermediate-time or back-up zones, the effect of wind stretching the arc should be considered, and then the operating time for which the relay is adjusted has an important bearing on the outcome.Tending to offset the longer time an arc ha

48、s to stretch in the wind when it is in the intermediate or back-up zones is the fact that, the farther an arcing fault is from a relay, the less will its effect be on the relays operation. In other words, the more line impedance there is between the relay and the fault, the less change there will be

49、 in the total impedance when the arc resistance is added. On the other hand, the farther away an arc is, the higher its apparent resistance will be because the current contribution from the relay end of the line will be smaller, as considered later.A small reduction in the high-speed-zone reach because o