For the 10kV side of the distribution transformer, a metal oxide lightning arrester should be installed. The closer to the transformer is installed, the better the protection effect is. It is generally required to be installed inside the drop fuse.
For the 10kV side of the distribution transformer, a metal oxide lightning arrester should be installed. The closer the transformer is installed, the better the protection effect is. It is generally required to be installed inside the drop fuse. The residual voltage of the arrester must be less than the withstand voltage of the distribution transformer to effectively protect the distribution transformer. The grounding terminal of the arrester should be connected directly to the metal casing of the distribution transformer. It is not allowed to ground the arrester independently through the down conductor. This is because the residual voltage of the arrester is only 17kV ~ 50kV. That is, the equivalent resistance under the impact is only 3.4 Ω to 10 Ω. However, the grounding resistance of an independent grounding may be about 10Ω, and even more in rural areas. Then, when the lightning current flows, the potential may be relatively high. If the lightning arrester is grounded independently, the two are superimposed and then applied to the transformer. May cause damage to the transformer insulation. If the grounding terminal of the arrester is directly connected to the metal casing of the transformer, the potential does not act on the insulation of the transformer, so the insulation of the transformer is safer. However, the potential of the metal casing of the transformer will be very high (equal to IR), and the inverter voltage from the metal casing of the transformer to the low voltage side may occur. Therefore, the neutral point on the low voltage side must also be connected to the metal casing of the transformer. This connection is called three points (the grounding end of the high voltage arrester, the neutral point of the low voltage winding, and the metal casing of the transformer). When the transformer capacity is 100kVA or more, the grounding resistance should be reduced to 4Ω or less as much as possible; when the transformer capacity is less than 100kVA, the grounding resistance can be less than 10Ω. When the three points are connected to ground, the high-voltage side is thundered. When the arrester is discharged, the transformer insulation is subjected to the residual voltage of the arrester, and the voltage drop on the grounding device does not act on the insulation of the transformer, thus protecting the transformer. It is advantageous to reduce the risk of insulation breakdown between the high voltage windings between the high and low voltage windings and the metal casing of the transformer. In order to prevent the impact of the instantaneous rise of the neutral point potential on the low-voltage side of the transformer on the safety of the user, an auxiliary ground line (repetitive grounding) can be installed near the user.
The transformer thus protected will also have some lightning accidents during operation. This is because the general distribution transformer is not equipped with a low-voltage arrester on the low-voltage side. At this time, not only the damage on the low-voltage side but also the high-voltage side may occur. There are three mechanisms for damage: Article source: (http://Read.aspx?NewsId=20)
(1) Light strikes the low-voltage line or the low-voltage line and is exposed to induced lightning, which damages the low-voltage side insulation.
(2) The low-voltage side is damaged by lightning on the high-voltage side. This is because at this time, by the electromagnetic coupling, an over-voltage (positive conversion process) proportional to the transformer ratio is also generated on the high-voltage side winding, due to the high-voltage side insulation. The degree is smaller than the low voltage side, so the high voltage side insulation may be damaged.
(3) The lightning strikes the high-voltage line or the high-voltage line and is exposed to the induced lightning. At this time, the lightning arrester acts to generate a voltage drop across the grounding resistance. This pressure drop will act on the low-voltage side neutral point, while the low-voltage side outgoing line, which is equivalent to grounding through the wire resistance, so most of the high potential generated on the ground line is added to the low-voltage side of the line.
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For the 10kV side of the distribution transformer, a metal oxide lightning arrester should be installed. The closer the transformer is installed, the better the protection effect is. It is generally required to be installed inside the drop fuse. The residual voltage of the arrester must be less than the withstand voltage of the distribution transformer to effectively protect the distribution transformer. The grounding terminal of the arrester should be connected directly to the metal casing of the distribution transformer. It is not allowed to ground the arrester independently through the down conductor. This is because the residual voltage of the arrester is only 17kV ~ 50kV. That is, the equivalent resistance under the impact is only 3.4 Ω to 10 Ω. However, the grounding resistance of an independent grounding may be about 10Ω, and even more in rural areas. Then, when the lightning current flows, the potential may be relatively high. If the lightning arrester is grounded independently, the two are superimposed and then applied to the transformer. May cause damage to the transformer insulation. If the grounding terminal of the arrester is directly connected to the metal casing of the transformer, the potential does not act on the insulation of the transformer, so the insulation of the transformer is safer. However, the potential of the metal casing of the transformer will be very high (equal to IR), and the inverter voltage from the metal casing of the transformer to the low voltage side may occur. Therefore, the neutral point on the low voltage side must also be connected to the metal casing of the transformer. This connection is called three points (the grounding end of the high voltage arrester, the neutral point of the low voltage winding, and the metal casing of the transformer). When the transformer capacity is 100kVA or more, the grounding resistance should be reduced to 4Ω or less as much as possible; when the transformer capacity is less than 100kVA, the grounding resistance can be less than 10Ω. When the three points are connected to ground, the high-voltage side is thundered. When the arrester is discharged, the transformer insulation is subjected to the residual voltage of the arrester, and the voltage drop on the grounding device does not act on the insulation of the transformer, thus protecting the transformer. It is advantageous to reduce the risk of insulation breakdown between the high voltage windings between the high and low voltage windings and the metal casing of the transformer. In order to prevent the impact of the instantaneous rise of the neutral point potential on the low-voltage side of the transformer on the safety of the user, an auxiliary ground line (repetitive grounding) can be installed near the user.
The transformer thus protected will also have some lightning accidents during operation. This is because the general distribution transformer is not equipped with a low-voltage arrester on the low-voltage side. At this time, not only the damage on the low-voltage side but also the high-voltage side may occur. There are three mechanisms for damage: Article source: (http://Read.aspx?NewsId=20)
(1) Light strikes the low-voltage line or the low-voltage line and is exposed to induced lightning, which damages the low-voltage side insulation.
(2) The low-voltage side is damaged by lightning on the high-voltage side. This is because at this time, by the electromagnetic coupling, an over-voltage (positive conversion process) proportional to the transformer ratio is also generated on the high-voltage side winding, due to the high-voltage side insulation. The degree is smaller than the low voltage side, so the high voltage side insulation may be damaged.
(3) The lightning strikes the high-voltage line or the high-voltage line and is exposed to the induced lightning. At this time, the lightning arrester acts to generate a voltage drop across the grounding resistance. This pressure drop will act on the low-voltage side neutral point, while the low-voltage side outgoing line, which is equivalent to grounding through the wire resistance, so most of the high potential generated on the ground line is added to the low-voltage side of the line.
Http://news.chinawj.com.cn Submission:
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