《第九章操作过电压与绝缘配合课件.ppt》由会员分享，可在线阅读，更多相关《第九章操作过电压与绝缘配合课件.ppt（72页珍藏版）》请在三一办公上搜索。
1、第九章 操作过电压与绝缘配合Chapter 9 Operation Over-voltage&Insulation Coordination,操作过电压通常具有幅值高、存在高频振荡、强阻尼和持续时间短的特点，危害性极大。,Typical over-voltage has a high amplitude.There are several harmful characteristics of high-frequency oscillation,strong damping and short duration.,常见的操作过电压主要包括：切断空载线路过电压、空载线路合闸过电压、切除空载变压器
2、过电压和断续电弧接地过电压这几种。Common over-voltage operations include:cutting off no-load lines,closing on no-load lines,removing no-load transformers and intermittent arc grounding.,绝缘配合是指综合考虑系统中可能出现的各种作用电压、保护装置特性及设备的绝缘特性，最终确定电气设备的绝缘水平。Insulation coordination is an integrated system considering various types of
3、over-voltage,insulation characteristics of protective devices and equipment,Which determine the insulation level of electrical equipment.,9.1 切断空载线路过电压(Cutting off no-load lines over-voltage)9.2 空载线路合闸过电压(Closing on no-load lines over-voltage)9.3 切除空载变压器过电压(Removing no-load transformers over-voltage
4、)9.4 断续电弧接地过电压(Intermittent arcing ground over-voltage)9.5 绝缘配合(Insulation coordination)习题和参考答案(Exercises and references),本章内容(Main content of this section),返回,9.1 切断空载线路过电压(Cutting off no-load lines over-voltage),切除空载线路是电网中常见操作之一，在切空载线路的过程中，虽然断路器切断的是几十安到几百安的电容电流，比短路电流小的多，但如果使用的断路器灭弧能力不强，在切断这种电容电流时就
5、可能出现电弧的重燃，从而引起电磁振荡，造成过电压。,Cutting off no-load lines is one of the common operations in power grid.In the process of cutting load line,although the circuit breaker cuts off the tens to hundreds ampere of capacitive current which is smaller than the short-circuit current,the arc may re-ignite,which ca
6、uses electromagnetic vibration,resulting in over-voltage if the circuit breakers capability to eliminate arc is not strong.,本节内容(Content of this section),9.1.1 产生原理(Generation theory)9.1.2 影响因素和降压措施(Influencing factors and reduce voltage measures),用单相集中参数的简化等效电路来分析，如图9-1，S断开之前线路电压UC(t)=e(t),设第一次熄弧（设
7、时间为t1）发生断路器的工频电容电流ic(t)过零时，如图9-2，线路上电荷无处泄放，uc(t)保留为Em，触头间电压ur(t)为:,9.1.1 产生原理(Generation theory),Single-phase lumped parameter circuit shown in figure 9-1 is used as the simplified equivalent circuit to analyze.Before S is disconnected line voltage UC(t)=e(t).Suppose the first arc extinction(the tim
8、e is t1)occurs when circuit breaker power frequency capacitive current ic(t)showed in figure 9-2 crosses zero.The charge in the line has no place to discharge,so uc(t)remains equaling Em.Contact voltage ur(t)is:Ur(t)=e(t)-Em=Em(coswt-1)(9-1),图9-1 切除空载线路时的等值计算电路图Fig9-1 Equivalent calculation circuit
9、diagram when cutting off the no-load lines,图9-2 切除空载线路过电压的发展过程Fig9-2 Over-voltage development of cutting off no-load lines,Half cycle later,e(t)=-Em.The voltage between two contacts recovers to 2Em.At the moment if dielectric insulation strength between the contacts has not been properly restored,or
10、 the strength of insulation recovery does not rise fast enough,the arc may re-ignite when t2,which is equivalent to an anti-polarity reclosing.,半周期后，e(t)=-Em，两触头间电压即恢复电压2Em。此时若触头间的介质绝缘强度没有很好恢复，或绝缘恢复强度的上升速度不够快，可能在t2时电弧重燃，相当于一次反极性重合闸。,UCmax达到-3Em，设在tt3时高频(重合闸过程，回路振荡的角频率,大于工频下的M)电容电流第一次过零时熄弧，uc(t)保持-3E
11、m，又过T2，e(t)又达最大值，触头间电压ur(t)为4Em。依此类推，直至触头间绝缘足够高，不再重燃为止。线路上的过电压将不断增大，一直达到很高的数值。,返回,图9-2 切除空载线路过电压的发展过程Fig9-2 Over-voltage develop process of cutting off no-load line,UCmax reaches-3Em,supposing at tt3 the high-frequency(re-closing process,loop oscillation angular frequency,is greater than M)capacitiv
12、e current crosses zero for the first time and arc is extinct.uc(t)remains-3Em.After T/2,e(t)reaches the maximum voltage.ur(t)is 4Em,and so on.Until the insulation between contacts is high enough,arc will no longer re-ignite.Over-voltage in lines will continue to increase to a very high value.,9.1.2
13、影响因素和降压措施(Influencing factors and reduce voltage measures),影响过电压的最大值的因素：(Influencing factors of the maximum over-voltage)1)断路器的性能；(The performance of circuit breakers)2)中性点接地方式；(Type of neutral grounding),3)母线上的出线数(The outlet number of bus)4)在断路器外侧装有电磁式电压互感器等设备(Electromagnetic voltage transformer an
14、d other equipment outside the circuit breakers)消除或降低操作过电压采取的措施如下：(Measures to eliminate or reduce the over-voltage are as follows:)（1）改善断路器的结构，避免发生重燃现象(Improve the structure of circuit breaker to avoid arc regenerating),（2）断路器加装并联电阻(Installing circuit breaker with parallel resistors)（3）利用避雷器保护(Use s
15、urge arresters to protect)（4）泄流设备的装设(Installing equipment for discharge),图9-3 带并联电阻断路器Fig9-3 Circuit breaker with parallel resistors 1主触头 2辅助触头 R并联电阻1Main contact 2Auxiliary contact RParallel resistors,产生原理(Generation theory)原理(Theory)优点(Benefits)缺点(Shortcomings)影响因素和降压措施(Influencing factors and red
16、uce voltage measures),小 结(Summary),影响过电压的最大值的因素（4点）Factors affecting the maximum over-voltage(4 points),返回,（本节完）,9.2 空载线路合闸过电压(Closing on no-load lines over-voltage),电力系统中，空载线路合闸过电压也是一种常见的操作过电压。通常分为两种情况，即正常操作和自动重合闸。由于初始条件的差别，重合闸过电压的情况更为严重。近年来由 于采用了种种措施（如采用不重燃断路器、改进变压器铁芯材料等）限制或降低了其他幅值更高的操作过电压，空载线路合闸过
17、电压的问题就显得更加突出。,Closing on no-load lines over-voltage is also a common over-voltage in power system.It is usually divided into two kinds that are normal operation and automatic reclosing.Due to differences in initial conditions,situation of reclosing over-voltage is worse.In recent years,because vario
18、us measures had been taken(such as using circuit breakers which are not renewed,improving transformers core materials,etc.)to limit or reduce the amplitude of other operation over-voltage with higher amplitude.The problem of the closing on no-load lines over-voltage becomes even more apparent.,本节内容(
19、Content in this section),9.2.1 发展过程(Develop process)9.2.2 影响因素和降压措施(Influencing factors and reduce voltage measures),这种操作通常出现在线路检修后的试送电。此时线路上不存在任何异常（如接地）。线路电压的初始值为零。正常合闸时，若三相接线完全对称，且三相断路器完全同步动作，则可按照单相电路进行分析研究。在这里我们用集中参数等值电路的方法分析这种过电压的发展机理。Such operation often appears in lines for trial immediately a
20、fter inspection of power lines.At the moment they are normal(such as grounding).The initial value of line voltage is zero.In normal closing operation,if three-phase connection are completely symmetrical,and three-phase circuit breakers have synchronized action,it can be analyzed as single-phase circ
21、uit.Here we use lumped parameter equivalent circuit to analyze the mechanism of development of the over-voltage.,1.正常合闸的情况(Normal conditions),9.2.1 发展过程(Develop process),图9-4 合闸示意图Fig 9-4 Closing diagram（a）集中参数等值电路（b）简化等值电路,(a)Lumped parameter equivalent circuit,(b)Simplified equivalent circuit,在图9-
22、4(a)所示的等值电路中，其中空载线路用一T型等值电路来代替,RT、LT、CT分别为其等值电阻、电感和电容，u为电源的电阻和电感。在作定性分析时，还可忽略电源和线路电阻的作用，这样就可进一步简化成图9-4(b)所示的简单振荡回路，其中电感。若取合闸瞬间为时间起算点(t0)，则电源电压的表达式为Figure 9-4(a)shows a equivalent circuit,which no-load line is replaced by a T-equivalent circuit.RT,LT,CT stand for the equivalent resistance,inductance
23、and capacitance respectively.u is power resistance and inductance.Power and line resistance can be ignored when making qualitative analysis.Thus it can be further simplified to a simple oscillator circuit shown in figure 9-4(b).If closing time is taken as starting-point(t=0),the power voltage can be
24、 described as followed.,（9-2）,（9-3）,U为稳态分量；(U the steady-state component),U 为自由振荡分量。(U free oscillation component),（9-5）,再者，电源是工频交流电压u(t),这时uc(t)表达式将为Furthermore,the power voltage u(t)is AC voltage.The expression of uc(t)will be,（9-4）,回路存在衰减的振荡，以衰减系数来表示：The attenuation oscillation exists in the loop
25、.Use attenuation coefficient to express oscillation:,波形如图9-5(b）Waveform is shown in Figure 9-5(b),图9-5 合闸过电压波形Fig 9-5 Closing over-voltage waveform(a)电源电压为直流电压(b)电源电压为工频交流电压,(a)DC supply voltage,(b)AC supply voltage,以上是正常合闸的情况，空载线路L没有残余电荷，初始电压UC(0)0。如果是自动重合闸的情况，那么条件将更为不利，主要原因在于这时线路上有一定残余电荷和初始电压，重合闸时
26、振荡将更加激烈。In normal closing conditions,there is no residual charge on no-load lines L.The initial voltage UC(0)=0.In automatic reclosing operation,the conditions will be more serious mainly because there is a certain residual charge and initial voltage.Thus the oscillation will be more intense when it
27、 is re-closed.,2.自动重合闸的情况(Automatic re-closing),自动重合闸是线路发生跳闸故障后，由自动装置控制而进行的合闸操作。,Automatic re-closing are operations carried out under the control of automatic equipment after a fault trip occurs on line.,图96为系统中常见的单相短路故障的示意图。在中性点直接接地系统中，A相发生对地短路，短路信号先后到达断路器Q2,Q1。断路器S2先跳闸，在断路器Q2跳开后，流过断路器Q1中键全相的电流是线路
28、电容电流，故当电压电流相位相差900时，断路器Q1跳闸。于是在健全相线路上将留有残余电压。,Figure 9-6 shows the common single-phase short-circuit in power system.In the neutral point direct grounding system,short circuit occurs when A-phase grounds.Short-circuit signal gets to circuit breakers Q2 and then Q1.The trip occurs first in the circui
29、t breaker S2.After that the line current in the key-phase flowing through the circuit breaker Q1 is capacitive current.So when the difference of voltage and current phase is 90 degree,the trip occurs in circuit breaker Q1.Residues will be left in normal phase voltage lines.,图9-6 重合闸示意Fig 9-6 Reclosi
30、ng diagram,设Q1重合闸之前，线路残余电压已下降30，即(10.3）(1.31.4 U)=(0.910.98)U。考虑最严重的情况，重合闸时电源电压为U，重合闸时暂态过程中过电压为U-U-(0.91.98)U=(-2.912.98)U。在实际过程中，过电压还要低些。在合闸过电压中，以三相重合闸的情况最为严重。,返回,Suppose before Q1 is reclosed,residual voltage on the line has dropped 30 percent,that is(1-0.3)(1.3 1.4 U)=(0.91 0.98)U.Considering the
31、 most serious case,the supply voltage is-U when re-closing and in the transient process of reclosing the over-voltage is-U+-U-(0.91.98)U=(-2.91 2.98)U.In practical process,over-voltage is even lower.In the closing over-voltage,the three-phase reclosing is the most serious condition.,1.合闸相位(Closing p
32、hase),合闸时电源电压的瞬时值取决于它的相位，相位的不同直接影响着过电压幅值，若需要在较有利的情况下合闸，一方面需改进高压断路器的机械特性，提高触头运动速度，防止触头间预击穿的发生；另一方面通过专门的控制装置选择合闸相位，使断路器在触头间电位极性相同或电位差接近于零时完成合闸。When closing the supply voltage,the instantaneous value depends on its phase.The phase difference directly affects the over-voltage amplitude.If we need to clo
33、se in more favorable circumstances,on the one hand we should improve the mechanical properties of high-voltage circuit breakers to increase the velocity of contact to prevent the pre-breakdown between contacts;on the other hand,use a special control device to select closing phase,so that circuit bre
34、aker can complete the closing when the polarities of the electric potential between contacts are the same or difference is close to zero.,2.线路损耗(Line Loss)线路上的电阻和过电压较高时线路上产生的电晕都构成能量的损耗，消耗了过渡过程的能量，使得过电压幅值降低。The corona produced when resistance and over-voltage on lines are high constitutes the energy
35、loss,which consumes the energy in the transition process to lower over-voltage amplitude.,In the automatic reclosing process,because there is a certain leakage resistance of insulators,about 0.5s interval period,residual voltage in line will drop 10%30%.Then it helps to reduce the magnitude of reclo
36、sing over-voltage.In addition,if the line-side access with electromagnetic voltage transformer,its equivalent inductance and equivalent resistance and line capacitance together constitute a damped oscillation circuit,so that the residual charge can discharge completely in a few power frequency cycle
37、s.,3.线路上残压的变化(Changes of residual in line)在自动重合闸过程中，由于绝缘子存在一定的泄漏电阻，大约有0.5s的间歇期，线路残压会下降1030。从而有助于降低重合闸过电压的幅值。另外如果在线路侧接有电磁式电压互感器，那么它的等值电感和等值电阻与线路电容构成一阻尼振荡回路，使残余电荷在几个工频周期内泄放一空。,整个合闸过程的两个阶段对阻值的要求是不同的：在合辅助触头2的第一阶段，R对振荡起阻尼作用，使过渡过程中的过电压最大值有所降低，R越大、阻尼作用越大、过电压就越小，所以希望选用较大的阻值；大约经过815ms，开始合闸的第二阶段，主触头1闭合，将R短接，使
38、线路直接与电源相连，完成合闸操作。,In the entire closing process,the requirements of resistance in two stages are different.In the first stage when closing the auxiliary contact 2,R damps the oscillation So that the maximum of over-voltage decreases in the transitional process.The larger R is,the greater the damping
39、 effect is.And then over-voltage is smaller.So a large resistance is favorable.After about 8 15ms,second stage of closing begins.The main contact 1 is closed,R shorted,so that the line is connected with the power directly to complete the closing operation.,在第二阶段，R值越大，过电压也越大，所以希望选用较小的阻值。因此，合闸过电压的高低与电
40、阻值有关，某一适当的电阻值下可将合闸过电压限制到最低。图9-7为500kV开关并联电阻与合闸过电压的关系曲线，当采用450的并联电阻时，过电压可限制在2倍以下。In the second stage,the greater value R is,the greater the over-voltage is.So smaller resistance is favorable.Therefore,the level of closing over-voltage is related to resistance values.An appropriate resistor value may
41、limit the closing over-voltage to a minimum.Figure 9-7 shows the relationship curve of 500kV switching parallel resistance and closing over-voltage,when using a 450 parallel resistance,over-voltage may be limited less than two times,图9-7 合闸电阻R与过电压倍数K0的关系Fig 9-7 The relationship between closing resis
42、tor R and the over-voltage multiple K0,（2）控制合闸相位(Control of closing phase)通过一些电子装置来控制断路器的动作时间，在各相合闸时，将电源电压的相位角控制在一定范围内，以达到降低过电压的目的。具有这种功能的同电位合闸断路器在国外已研制成功它既有精确、稳定的机械特性、又有检测触头间电压(捕捉向电位瞬间)的二次选择回路。The circuit breaker operating time can be controlled by electronic devices.During the closing pesiod of ea
43、ch phase,the phase angle of supply voltage is controlled in a certain range in order to achieve the purpose of reducing over-voltage.The potential closing circuit breakers with this function have been developed in foreign countries,which have both accuracy and stable mechanical properties and the se
44、cond selection circuit,detecting the voltage between contacts(capturing the potential moment).,（3）利用避雷器来保护(Protecting using the surge arresters)安装在线路首端和末端(线路断路器的线路侧)的ZnO或磁吹避雷器，均能对这种过电压进行限制，如果采用的是现代ZnO避雷器，就有可能将这种过电压的倍数限制到1.51.6。ZnO or magnetism blowing arrester installed at the line head and end(line
45、 side of line circuit breaker)can limit this kind of overvoltage.There is possibility to limit this kind of overvoltage multiple by 1.51.6 times if modern ZnO arrester is,发展过程(Develop process)正常合闸的情况(The normal closing condition)自动重合闸的情况(Automatic re-closing condition)影响因素和降压措(Influential factors an
46、d step-down measures)合闸相位(Closing phase)线路损耗(Line Loss)线路残余电压的变化(Residual changes in line voltage),小 结(Summary),返回,（本节完）,9.3 切除空载变压器过电压 Removal of no-load transformer over-voltage,正常运行时,空载变压器表现为一励磁电感。切除空载变压器就是开断一个小容量电感负荷，会在变压器和断路器上出现很高的过电压。开断并联电抗器、电动机等，也属于切断感性小电流的情况。During the normal operation,no-lo
47、ad transformer acts as an excitation inductor.Removal of no-load transformer is breaking a small-capacity inductance load,and a high over-voltage will appear on transformers and circuit breakers.Breaking shunt reactor,motor,are also belong to the situation of cutting off a small emotional current.,本
48、节内容(Content of this section),9.3.1 发展过程(Development)9.3.2 影响因素与限制措施(Influencing factors and restrictive measures),变压器和断路器上出现过电压的原因是变压器的空载电流过零前就被断路器强制熄弧而切断，导致全部电磁能量转化为电场能量而使电压升高。The reason why over-voltage appears on transformer and circuit breaker is that before transformer no-load current crosses z
49、ero,it has been shut off by circuit breaker mandatory extinction.All the electromagnetic energy is changing into electric energy which increases voltage.,9.3.1 发展过程(Development),研究表明：切断100A以上的交流电流时，开关触头间的电弧通常是在工频电流自然过零时熄灭的；当所切除的电流很小时（变压器的空载电流非常小，只有几安到几十安），电弧往往提前熄灭，亦即电流会在过零之前就被强行切断，即所谓的截流现象。It is dem
50、onstrated that when cutting off current is more than 100A AC,the arc usually extinguishes when frequency current is over zero naturally between contacts.When the current to be removed is very small(the transformer no-load current is very small,only a few AN to scores AN),the arc often extinguishes b
