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1、9.4 断续电弧接地过电压 9.4 Intermittent arc grounding over-voltage,中性点不接地电网中的单相接地电流(电容电流)较大，接地点的电弧将不能自熄，而以断续电弧的形式存在，就会产生另一种严重的操作过电压断续电弧接地过电压。 The single-phase grounding current in ungrounded power grid (capacitive current) is large. Then the arc in the place will not self-extinguish and exist in the form of
2、intermittent arc which creates another serious over-voltage intermittent arcing grounding over-voltage.,断续电弧接地过电压出现在下列三种情况下后果比较严重： Intermittent arc grounding over-voltage appearing in the following three cases will result in more serious consequences: 系统中有一些弱绝缘的电气设备 There is some electrical equipmen
3、t of weak insulation in system 设备绝缘在运行中可能急剧下降 Equipment insulation may sharply decline 设备绝缘中有某些潜伏性故障 There are some latent failures in equipment insulation,9.4.1 发展过程 Development process 9.4.2 防护措施 Precaution measurements,本节内容 Contents in this section,这种过电压的发展过程和幅值大小都与熄弧时间有关。存在两种熄弧时间： The developmen
4、t and amplitude of such over-voltage are related with extinction time of arc. There are two arc blow-out time:,电弧在过渡过程中的高频振荡电流过零时即可熄灭 Arc can extinct when high-frequency oscillation is over zero in the transition process 电弧的熄灭发生在工频电流过零的时刻 Extinction of the arc occurs at the power frequency current z
5、ero-crossing time,9.4.1 发展过程 9.4.1 Development process,下面假定电弧的熄灭发生在工频电流过零的时刻，来说明这种过电压的物理发展过程： Assuming extinction of arc occurs at the power frequency current zero moment. To illustrate the physical development of this over-voltage :,作如下简化： Make the following simplification: (1) 略去线间电容的影响； Omit the
6、current impact between lines; (2) 设各相导线的对地电容均相等，即C1=C2=C3=C。就可得如图9-10(a)所示的等值电路。 Assuming each phase conductor located on the ground capacitors are equal . That is, C1 = C2 = C3 = C. Equivalent circuit is shown in Figure 9-10 (a).,图9-10 单相接地故障电路图和向量图 Fig 9-10 Single-phase ground fault circuit and ve
7、ctor diagram,Assuming ground fault occurs in the A-phase when passes rightly through the magnitude of . So that the potential A phase conductor immediately becomes zero and the neutral point potential increases from zero to phase voltage. That is, , B, C two-phase-to-ground voltages are increased to
8、 a line voltage of , .,设接地故障发生于A相，而且是正当 经过幅值 时发生，这样A相导线的电位立即变为零，中性点电位 由零升至相电压，即 ，B、C两相的对地电压都升高到线电压 、 。,如以uA，uB，uC代表三相电源电压；以u1，u2，u3代表三相导线的对地电压，即C1、C2、C3上的电压，则通过分析可得如图9-11所示的过电压发展过程。,If uA, uB, uC stand for three-phase power supply voltage and u1, u2, u3 are on behalf of three-phase conductors to gro
9、und voltage, that is, the voltage on C1 C2, C3, then by analyzing the development of over-voltage can be shown in figure.,图9-11 在工频电流过零时的熄弧的 断续电弧接地过电压的发展过程,Fig.9-11 In the current zero-frequency arc quenching Intermittent arcing ground voltage over the development process,按工频电流过零时熄弧的理论分析得出的结论是： The
10、conclusion analyzed by the theory that frequency-current is extinct when over zero is (1) 非故障相上的最大过电压为3.5倍； The maximum over-voltage on the non-fault phase is 3.5 times; (2) 故障相上的最大过电压为2.0倍。 The maximum over-voltage on the fault phase is 2.0 times.,长期以来大量试验研究表明：故障点电弧在工频电流过零时和高频电流过零时熄灭都是可能的。 For a lo
11、ng time, a large number of pilot studies have shown that: the extinction of fault point arc is possible when the power frequency arc-current and high-frequency are over zero.,发生在大气中的开放性电弧往往要到工频电流过零时才能熄灭；在强烈去电离的条件下，电弧往往在高频电流过零时就能熄灭。 Open electric arc occurring in the atmosphere can extinguish when th
12、e power frequency electric current is over zero. In intense ionizes condition, the electric arc has often been able to extinguish in the high-frequency current zero hour.,电弧的燃烧和熄灭会受到发弧部位的周围媒质和大气条件等的影响，具有很强的随机性质，因而它所引起的过电压值具有统计性质。 Arc burning and extinction will be affected by the media and atmospher
13、ic conditions around the parts of arc, having highly random nature. And therefore the over-voltage it raises has a statistical nature.,9.4.2 防护措施 9.4.2 Precautions,为了消除电弧接地过电压，最根本的途径就是消除间歇性电弧，可以通过改变中性点接地方式来实现。 In order to eliminate arc grounding over-voltage, the most fundamental way is to eliminate
14、 intermittent arc which can be achieved by changing the neutral point grounding form.,1. 采用中性点直接接地方式 Neutral point direct grounding,若中性点接地，单相接地故障将在接地点产生很大的短路电流，断路器将跳闸，从而彻底消除电弧接地过电压。目前，110kV及以上电网大多采用中性点直接接地的运行方式。 If the neutral point is grounded, single-phase ground fault will produce great short-cir
15、cuit current in the grounding point, circuit breaker will trip, totally eliminating arc grounding over-voltage. At present, grid of 110kV and above it uses the mode of the neutral point direct grounding.,2. 采用中性点经消弧线圈接地方式 Neutral-point arc suppression coil grounding method,采用中性点直接接地方式虽然能够解决断续电弧问题，但每
16、次发生单相接地故障都会引起断路器频繁跳闸，严重影响供电的连续性。所以，我国35kV及以下电压等级的配电网采用中性点经消弧线圈接地的运行方式。 Neutral-point direct grounding can solve the problem of intermittent arc. Every occurrence of a single-phase ground fault causes circuit breaker to trip frequently, seriously affecting the continuity of electricity supply. So in network of 35kV and below neutral-point arc suppression coil grounding method is used.,消弧线圈是一个具有分段铁芯、电感可调的电抗器，其伏安特性不易饱和，如图9-12所示。 Petersen-coil is a rea
