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1、9.2 空载线路合闸过电压 9.2 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 usual
2、ly 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
3、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 .,9.2.1 发展过程 9.2.1 Develop process 9.2.2 影响因素和降压措施 9.2.2 Influencing factors and reduce voltage measures,本
4、节内容 Contents in this section,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 i
5、nitial 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
6、development of the over-voltage.,正常合闸的情况 Normal conditions,9.2.1 发展过程 9.2.1 Develop process,图9-4 合闸示意图 Fig 9-4 Closing diagram （a）合闸空载线路过电压时集中参数等值电路（b）简化等值电路,Closing load line lumped parameter equivalent circuit when the overvoltage,(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
7、,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 and capacitance respe
8、ctively. 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
9、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. Use
10、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
11、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 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 in
12、tense 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。,Figure 9-6 shows the
13、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.,图9-6 重合闸示意 Fig 9-6 Reclosing diagram,图9-6 重合闸示意 Fig 9-6 Reclosing diagram,断路器S2先跳闸，在断路器Q2跳开后，流过断路器
14、Q1中键全相的电流是线路电容电流，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。 The trip occurs first in the circuit 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 c
15、ircuit breaker Q1. Residues will be left in normal phase voltage lines.,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。,Suppose before Q1 is reclosed, residual voltage on the line has dropped 30
16、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 9.2.2 Influential factors an
