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Research on Protection Measures of Distribution Transformer

2020-10-16 15:09:50
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The normal operation of Transformer directly affects the production and living power consumption of users, and is related to the safety of electrical equipment. In order to ensure that users use high-quality and safe electricity, it is necessary to ensure the normal operation of distribution transformer. This paper specifically discusses the maintenance measures and precautions of distribution transformer in daily use.




The distribution transformer is a kind of stop electric appliance in the distribution system, which transforms the communication voltage and current according to the law of electromagnetic induction. Usually installed in the pole, stand or distribution station, the voltage of 6-10 kV is generally reduced to about 400 V, which is input to users. Therefore, it is necessary for us to talk about the maintenance measures and precautions of distribution transformer from the perspective of maintenance equipment skills and daily operation, so as to ensure the normal operation of distribution transformer and ensure the safe use of electricity by users.




1. Maintenance equipment skills




1.1 install arrester for maintenance to avoid lightning overvoltage




Distribution transformer is a very important equipment in the distribution network. Once lightning damage occurs, it will cause power failure, directly affecting the industrial and agricultural production and people's life. Therefore, when conditions permit, it is better to use arrester for maintenance. In the system with ungrounded neutral point, the maintenance method of two-phase valve type arrester phase maintenance gap can also be used. However, in the same distribution network, it is necessary to install all gaps on the same phase conductor, so as to save a valve type arrester and avoid adding the number of line trips.




Valve type arrester, tube type arrester or maintenance gap of maintenance transformer shall be as close as possible to the transformer device. The closer the distance is, the better the maintenance effect will be. Generally, it is required to be installed inside the fuse on the high voltage side of transformer. The grounding wire shall be connected with the metal shell of distribution transformer and the neutral point at low voltage side. When the transformer capacity is 100ky; a and above, the grounding resistance should be reduced to less than 4 Ω; when the transformer capacity is less than 100kV; a, the grounding resistance should be less than 10 Ω. When the transformer is connected to the high voltage winding and the lightning arrester, it is beneficial to maintain the insulation between the transformer and the ground Risk. However, in order to avoid the impact of the instantaneous increase of neutral point potential on the safety of users, auxiliary grounding wire can be installed near the user.




The over-voltage of distribution transformer may be divided into two situations: (1) positive transformation: when the lightning wave reaches the low-voltage winding of the transformer connected with y and y, the breakdown installed at the neutral point is safely broken down, or when the lightning wave reaches the low-voltage winding of the transformer connected with y and YN, the electromotive force will be induced by the impulse current passing through the low-voltage winding of the transformer under the effect of external voltage And the neutral point voltage of high voltage winding is increased. (2) Reverse transformation: when the 10ky side is struck by lightning, a large lightning current will pass through the arrester, and a voltage drop will occur on the grounding device. This voltage drop will effect on the neutral point of the low-voltage winding and add it to the low-voltage winding. After electromagnetic induction, the high-voltage side will also present high-voltage. For the star connected transformer, the neutral point on the high-voltage side will also show insulation resistance Risk of high voltage. In addition, lightning arresters or breakdown Stabilizers can be installed at the low voltage side of the transformer according to the specific conditions, which can further improve the safety and reliability of the transformer.




The operation experience has proved that although the distribution transformer in the lightning area is equipped with valve type arrester for maintenance, there are still many damages caused by lightning strike. According to the accident lessons, in order to reduce the distribution transformer accident, the following technical measures should be taken according to the specific situation: (1) eliminate the weak insulation of distribution transformer. In the operating blade, the test and analysis of transformer insulating oil should be strengthened. Because the deterioration of insulating oil will directly lead to the decline of winding insulation, it is necessary to deal with or replace the problem in time. Extensive impulse test and turn to turn test on distribution transformer can effectively find out the insulation defects of transformer, timely organize maintenance, and reduce lightning damage accidents. (2) for distribution transformer installed on wooden pole line, maintenance gap can be installed in the incoming section of transformer, or the iron pin of top phase insulator with triangular conductor can be grounded to reduce lightning invasion The steepness of the wave and the reduction of the current flowing through the valve arrester. (3) A group of inductance coils (about 30 turns, 24cm in length, 20cm in diameter and about 100 μ h in inductance) can be added between the distribution transformer and the valve type arrester to limit the steepness of the lightning intrusion wave and reduce the Overvoltage on the insulation between transformer windings.


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SHANGHAI ZHENHUA TRANSFORMER MFG CO., LTD.

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