In addition to ensuring safety, the correct installation method of the lightning arrester will directly affect the working efficiency of the lightning arrester. It can be known from the general lightning arrester connection diagram. It is proved from the actual measurement that the length of the connecting line, the number and its connection method directly affect its voltage drop. This is because the voltage value on the connecting line is mainly determined by its inductance value, and the inductance value of the line is affected by its length and The connection method affects the following four ways to reduce the inductive voltage of the parallel lightning arrester:
1) The shorter the connection line, the smaller the inductance value, which means that the inductive voltage is smaller. Therefore, the length of the cable should be less than 25cm.
2) On the other hand, when the induced current flows through any two connecting lines, two magnetic fields in opposite directions are generated, so if each set of connecting lines can be tightly tied together, the two magnetic fields cancel each other out to make electricity The inductive voltage is greatly reduced.
3) When the length of the cable exceeds the maximum length of 25cm, we can use a set of connecting lines as shown. Since a set of lines is added, the inductor current is divided equally between the two sets of lines, so the resulting magnetic field strength is also reduced by half, which also means that the induced voltage can be reduced to an acceptable level. (<700v)
4) Since parallel power supply lightning arresters are generally installed in or above the distribution box, in many cases the ground wire is longer than other connection wires (more than 25cm), so that two ground wires can be used, one for grounding. The stick is connected to the metal casing of the distribution box. Series surge arresters can also be used to reduce the inductive voltage, as detailed below:
A. According to CCITT, BS and IEC standards, the instantaneous overvoltage and current on the signal and data lines are generally 5KV and 125KA, which is lower than the value on the power line. Therefore, it is recommended that the lightning flux can be no longer than 1 meter. Ground the cable, of course, if possible, make it as short as possible.
B. If the grounding is longer than 1 meter, such as 2 meters, 3 meters or 4 meters, the following cables may be used, but the cables must be separated by at least 5 cm.
Resistive voltage drop
Inductive voltage drop
Cable size (mm2)
Voltage drop (volts / meter)
Cable size (mm2)
Inductance value (H / m)
Voltage drop (V / m)
1
51.6
1
1.2
450
2.5
20.6
2.5
1.1
376
4
12.9
4
1.1
376
6
8.6
6
1
342
10
5.16
10
1
342
100
0.516
100
0.7
239
Can you reduce the inductive voltage by using a thicker connection?Since the transient voltage drop is much larger than the resistive voltage drop even more than 10 times when the transient overvoltage passes through the cable, the thicker cable can only slightly improve the pass voltage and cannot solve the problem.
Other installation considerations:
1. When the load is not more than 63A and the line is 4mm2 thick or the load is not more than 100A and the line is 10mm2 thick, the fuse can be avoided, but if the load is too large, the fuse or circuit breaker should be used. The role is to prevent the cable from being melted when the external wiring is shorted instead of protecting the lightning arrester itself.
2, most power supply lightning protection manufacturers are recommended to install the first load output of the power distribution screen as shown. In addition, if the load is also likely to generate a transient overvoltage and is fed back to the power supply, an additional lightning protection device is required.
3. If the three-phase power supply does not have a neutral line, the neutral line of the lightning protection device must be connected to the ground of the power supply.
4. In the case of an earth leakage circuit breaker, the lightning protection device must be installed in front of the earth leakage circuit breaker. The layout of the input and output lines of the series lightning arrester has a great impact on its performance. Since the power supply of the output line is generally acceptable after isolation by the lightning arrester, if it is too close to the input line, an instantaneous overvoltage will be sensed from the input line to the output line.
The grounding method also plays a key role in whether the lightning protection device can perform its intended function. As shown in the "relative" grounding mode, the expected function can be achieved, but if the "absolute" grounding method is used, that is, independent grounding, and such grounding generally has a resistance of 10 ohms or more, it is assumed that there is a transient current flow of 100A. When it is out of date, there will be at least 1000V of voltage coming out, and this voltage plus the lightning arrester itself can be damaged by the voltage that will be protected.
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