第九章操作过电压与绝缘配合课件

单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,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 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),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,(,E,xercises,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 causes 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,U,C,(t)=e(t),设第一次熄弧（设时间为,t,1,）发生断路器的工频电容电流,i,c,(t),过零时，如图,9-2,，线路上电荷无处泄放，,u,c,(t),保留为,E,m,，触头间电压,u,r,(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,U,C,(t)=e(t).,Suppose the first arc extinction (the time is,t,1,) occurs when circuit breaker power frequency capacitive current,i,c,(t),showed in figure 9-2 crosses zero. The charge in the line has no place to discharge , so,u,c,(t),remains equaling,E,m,. Contact voltage,u,r,(t),is :,U,r,(t)=e(t)-E,m,=E,m,(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 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)=-E,m.,The voltage between two contacts recovers to 2,E,m,. At the moment if dielectric insulation strength between the contacts has not been properly restored, or the strength of insulation recovery does not rise fast enough, the arc may re-ignite when,t,2, which is equivalent to an anti-polarity reclosing.,半周期后，,e(t)=-,E,m,，两触头间电压即恢复电压,2,E,m,。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,t,2,时电弧重燃，相当于一次反极性重合闸。,U,Cmax,达到,-3,E,m,，设在,t,t,3,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，,u,c(t),保持,- 3,E,m,，又过,T,2,，,e(t),又达最大值，触头间电压,u,r,(t),为,4,E,m,。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,U,Cmax,reaches,-3,E,m, supposing at,t,t,3,the high-frequency (re-closing process, loop oscillation angular frequency, is greater than M) capacitive current crosses zero for the first time and arc is extinct.,u,c(t),remains,- 3,E,m,. After T / 2,e(t),reaches the maximum voltage.,u,r,(t),is,4,E,m, 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,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 and 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 surge 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,1,Main contact 2,Auxiliary contact R,Parallel 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 reduce 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 various 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,(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 after 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 circuit. 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,9-4(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,R,T,、,L,T,、,C,T,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,(t,0),，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. R,T, L,T, C,T,stand for the equivalent resistance, inductance 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 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,u,c,(t),表达式将为,Furthermore, the power voltage u (t) is AC voltage. The expression of,u,c,(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. 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,U,C,(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，重合闸时振荡将更加激烈。,In normal closing conditions, there is no residual charge on no-load lines L. The initial voltage,U,C,(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 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,9,6,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,Q,2,Q,1,。断路器,S,2,先跳闸，在断路器,Q,2,跳开后，流过断路器,Q,1,中键全相的电流是线路电容电流，故当电压电流相位相差,90,0,时，断路器,Q,1,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 Q,2,and then Q,1,. The trip occurs first in the circuit breaker S,2,. After that the line current in the key-phase flowing through the circuit breaker Q,1,is capacitive current. So when the difference of voltage and current phase is 90 degree, the trip occurs in circuit breaker Q,1,. Residues will be left in normal phase voltage lines.,图,9-6,重合闸示意,Fig 9-6 Reclosing diagram,设,Q,1,重合闸之前，线路残余电压已下降,30,，即,(1,0.3,）,(1.31.4 U,)=(0.91,0.98 )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,=(-2.91,2.98) 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 Q,1,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 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.,9.2.2,影响因素和降压措施,(Influential factors and step-down measures),以上对合闸过电压的分析也是考虑,最严重的条件、最不利,的情况。实际出现的过电压幅值会受到一系列因素的影响，最主要的有：,The above analysis of closing over-voltage conditions is in,the most serious, the most adverse,circumstance. The actual over-voltage amplitude will be subject to a number of factors. The most important ones are:,合闸相位,(,Closing phase),线路损耗,(,Line Loss),线路残余电压的变化,(Changes of residual in line),1.,合闸相位,(,Closing phase),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 close 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 breaker 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 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 reclosing 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 cycles.,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,10,30,。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。,合闸过电压的限制、降低措施主要有,:,(Limit and reducing measures of closing over-voltage are:),(,一,),装设并联合闸电阻,最有效的措施,(,Installation of,co-gate resistance - the most effective measure),图,9-3,带并联电阻断路器,Fig 9-3 Circuit breaker with parallel resistance,如图,9-3,所示，这时应先合辅助触头,2,、后合主触头,1,。,As shown in Figure 9-3,auxiliary contact 2 should be first closed, and then the main contact 1should be closed.,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,8,15ms,，开始合闸的第二阶段，主触头,1,闭合，将,R,短接，使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 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 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,K,0,的关系,Fig 9-7 The relationship between closing resistor R and the over-voltage multiple,K,0,（,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 each 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 second 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,1.5,1.6,。,ZnO or magnetism blowing arrester installed at the line head and end (line 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 and 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-load 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 zero, 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 demonstrated 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 beforehand. That is to say the currents will be forcibly cut off before they are over zero, that is, the phenomenon of the so-called,closure,.,可用图,9-8,所示的简化,等值电路,来说明这种过电压的发展过程。图中 为变压器的激磁电感， 为变压器绕组及连接线的对地电容。,Figure 9-8 shows the simplified,equivalent circuit,to illustrate the development of over-voltage. In the figure for the transformer magnetizing inductance, for the transformer winding and connecting the line-to-ground capacitance.,图,9-8,切除空载变压器的理想等值电路,Fig 9-8 The ideal,equivalent circuit,of removal of no-load transformer,假如空载电流 时发生截断（即由 突然降到零），此时电源电压为 ，则切断瞬间在电感 和电容 中所储存的能量分别为,:,If the no-load current of truncation occurs (that is suddenly reduces to zero ), at this time the supply voltage is , then the moment when cut off the energy stored in the inductor and capacitor , which are showed below:,此后即在 、 构成的振荡回路中发生电磁振荡，在某一瞬间，全部电磁能量均变为电场能量，这时电容 上出现最大电压,Thereafter electromagnetic oscillations occur at oscillation circuit composed by,、,. In a certain moment, all the electromagnetic energy transforms into electric energy, at this time maximum of voltage,appears,in capacitor .,式中,变压器的特性阻抗,- transformer characteristic impedance,若略去截流瞬间电容上所储存的能量 ，则,If omitting the energy stored in capacitors at the closure moment.,截流现象,通常发生在,电流曲线的下降部分,，设 为正值，则相应的 必为负值。当开关中突然灭弧时， 中的电流 不能突变，将继续向 充电，使电容上的电压从“ ”向更大的负值方向增大，如图,9-9,所示。,The,closure phenomenon,usually occurs in,the decline part of current curve,. is positive, the corresponding must be negative. When the arc extinguishes suddenly in the switch, the current can not mutate, continuing to charge to , so that the voltage on the capacitor from the “ to a greater increase in negative direction, as shown in Figure 9-9.,此后，在 回路中出现,衰减性振荡,，其频率为,Since then, in the loop,attenuation of oscillation,appears, its frequency is,图,9-9,截流前后变压器上的电压和电流波形,Fig 9-9 The transformer voltage and current waveforms before and after closure,以上介绍的是理想化了的切除空载变压器过电压的发展过程，实际过程往往要复杂得多，断路器触头间会发生多次,电弧重燃,。与切除空载线路的情况相反，重燃对降低过电压是有利因素。,变压器参数,也会影响切空变过电压的幅值。实际的过电压将大大低于理想情况下的过电压。,Description above is the idealized development of removing no-load transformer over-voltage. The actual process is often much more complex. Between circuit breaker contacts the,arc renewal,will occur several times. Opposite to the removal of no-load lines, renewal is a positive factor to reduce over-voltage.,Transformer parameter,also affects the amplitude of no-load voltage. The actual over-voltage would be significantly lower than the over-voltage in ideal case.,返回,9.3.2,影响因素和限制措施,(Influencing factors and restrictive measures),影响因素及对应的限制措施主要有：,(Influence factors and the restrictive measures include:),1,、断路器性能,(,Circuit Breaker Performance ),切断小电流的电弧时性能越好的断路器，其切空变过电压的幅值越高。,When cutting off the arc of small current, the better the performance the circuit breakers is, the higher amplitude of