According to delimit, before the thunderstorm season every year, should make a preventive test of the lightning arrester, the difference of the lattice to timely exchange.

According to the above situation, in order to prevent the overvoltage caused by the forward transformation and the reverse transformation, the high and low voltage of the distribution transformer must be installed on both sides of the lightning arrester protection, if only on one side of the lightning arrester, or a side of the lightning arrester damage, will cause the damage of the distribution transformer due to lightning.

4 The distribution transformer is damaged because the grounding resistance is too high

In high terrain, the resistivity is higher. Therefore, the grounding lead of the arrester should be welded or bolted when installed. Therefore, the general mountain distribution transformer configuration in addition to consider the load center, in dealing with the low voltage outlet at the same time, to try to pay attention to avoid lightning strike area, do not install the distribution transformer at the high point, and do lightning protection measures. Some grounding leads are not firmly connected.

6 The distribution transformer in the lightning strike area should be properly replaced

For lightning, the commanding point is just the most vulnerable to lightning strike or induction discharge zone.

3 The grounding lead of the arrester does not meet the requirements of regulations, so that the lightning current cannot be discharged into the earth

The investigation found that some grounding leads are connected with tied wires, and the days are long and loose. The leading line should not be less than 16mm2 for copper wire and 25mm2 for steel wire. After the grounding resistance is reduced, the voltage amplitude generated by the "reverse transformation voltage" can be weakened when the low-voltage side is struck by lightning, and the damage caused by lightning can be reduced. According to the demarcations, the grounding resistance of the transformer with a capacity of 100kVA or above shall not be greater than 4 ω, and the repeated grounding points of each outlet of the transformer shall not be less than three, and the grounding resistance value shall not be greater than 10 ω; The ground resistance of a transformer with a capacity of less than 100kVA should not be greater than 10 ohms. Each outgoing line should have at least three repeat ground points, and the ground resistance should not be greater than 30 ohms. In the mountainous area to achieve this requirement, generally very difficult, the method is to increase the grounding pole as far as possible, extend the grounding line, and the grounding pole into the valley, the pond, or the use of Franklin resistance reducer to improve the previous technology. Therefore, for the high voltage side, the arrester should be installed at the lower end of the high voltage drop type fuse. 

In order to prevent this phenomenon, the insulator iron foot of the high-voltage line can be well grounded at the base or base pole of the distribution transformer. In this way, when lightning strikes, the lightning voltage breaks down the insulator to discharge to the ground, which can prevent the arrester and transformer from directly bearing too steep lightning current and ensure the safety of the distribution transformer. Because, even if the 0.6m long ground line, its inductance L is about 1mH, at the small thunder wave steepness of 10kA/μs, the ground line voltage drop is nearly 10kV, such a large value. This can not only reduce the length of the grounding lead, but also bring benefits to the installation of the arrester pre-test, as long as the fall type fuse, good safety measures can be carried out, will not affect the operation of the high-voltage line; Secondly, when the quality of the arrester is poor and the discharge arc cannot be extinguished, the continuous current of the power frequency will fuse the high-voltage drop type fuse and the melting pipe will fall automatically, which can avoid the influence on the power supply of the high-voltage line and reduce the tripping rate of the line. And often carry out inspection, found loose or missing, should be dealt with in time. Some grounding leads are lost or cut off due to external forces.

.

1. No handover test has been done before the installation of the arrester, and the damage of the arrester has not been discovered in time

Due to these reasons, no lightning arrester when struck by lightning, lightning directly lead to the breakdown on the distribution transformer burn out, so the arrester before installation, must first check the nameplate, its specification is consistent with the requirements of installation site, response to lightning arrester on a handover testing at the same time, its function must meet the factory scale, various parts should be intact, No damage to the porcelain sleeve, the surface should be clean.

In addition, the arrester ground lead (that is, the connection between the transformer housing) as short as possible.

(2) Inverse transformation: When high side suffer lightning strike, lightning arrester is larger, the current on the grounding device to produce voltage drop, the pressure drop and effect on the low voltage winding of neutral point, and on the low voltage winding, by electromagnetic induction will feedback is high voltage on the high side, the y connection of distribution transformer, high voltage on the neutral point will also flush is dangerous overvoltage for insulation. In addition, the grounding device is divided to increase the grounding resistance, when the lightning smooth flow through the arrester through the grounding pole to the earth discharge, because the grounding resistance is large, it will hinder the discharge of lightning current, a department of lightning current will impact to the transformer or line, causing damage to electrical equipment. When the arrester is installed and fixed, its upper end is connected with the phase line, the lower end of the grounding protection line, do not reverse; The interval between phases shall not be less than the designation of the installation design regulations; The arrester should be inspected and inspected regularly during operation, and pay attention to whether the porcelain sleeve is complete and whether there is any flashover trace; Whether the lead connection and grounding are firm and reliable.

2 The positive and negative overvoltage damages the distribution transformer

When a high-voltage arrester is installed on the high-voltage side of the transformer, but no arrester is installed on the low-voltage side of the transformer, the lightning protection grounding and the working grounding share a set of ground devices, and the overvoltage generated on the distribution transformer can be divided into two situations:

(1) positive transformation: when the low-voltage side is struck by lightning, the impulse current through the secondary winding of the transformer will induce the electromotive force according to the variable ratio and increase the voltage at the neutral point of the high-voltage winding, which may cause insulation breakdown. It and the arrester residual pressure superimposed on the transformer insulation, will greatly aggravate the damage.

It can be seen that it is necessary to install a lightning arrester on the low-voltage side of the distribution transformer, because it is not familiar with it before, and there have been many lessons. Now the installation of a lightning arrester on the low-voltage side of the distribution transformer is of great significance to reduce accidents and improve the reliability of power supply. What we need to pay attention to here is that the high and low voltage arrester grounding line and the transformer shell should be grounded together, and it should be firm and cannot be loosened, otherwise it can not play a lightning protection role.

5 Lightning slope is too steep when lightning strikes

Because the distribution transformer lightning protection valve type lightning arrester discharge needs a certain time, the lightning current steep is too large, the lightning voltage on the arrester rises too fast, the arrester valve plate is not enough to discharge, so that the lightning voltage is directly added to the distribution transformer to be protected, breakdown insulation cause burning. When the arrester moves, it will burn off the connection and cannot play the role of lightning protection.