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Talking about the problems of DC withstand voltage test of high voltage cable

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Talking about the problems of DC withstand voltage test of high voltage cable

作者: Release Date: 2018-07-09 Author: Click:

Talking about the problems of DC withstand voltage test of high voltage cable


With the advancement of national projects such as "west-to-east power transmission" and "south-to-north power transmission", high-voltage DC cables will become the main force for application. Large-scale access to new energy sources and the cabled construction of urban transmission require the use of high-voltage DC cables. HVDC cables are also a means of power transmission for offshore wind power and offshore islands.


High-voltage and ultra-high-voltage cables have become an indispensable material for modern urban power grid projects. However, the field of high-voltage and ultra-high-voltage cables in China has started late. Materials, equipment and manufacturing technologies have long relied on introduction and imitation. Now let's talk about what aspects of the problems with the DC voltage test of high-voltage cables?


1. The electric field distribution of cable insulation under DC voltage depends on the volume resistivity of the material, and the electric field distribution under AC voltage depends on the dielectric constant of each medium, especially the DC current in cable accessories such as cable terminal heads, joint boxes, etc. The distribution of field strength and the distribution of AC electric field strength are completely different, and the mechanism of insulation aging under DC voltage and the aging mechanism under AC voltage are different. Therefore, the DC withstand voltage test cannot simulate the operating conditions of high-voltage cables.


2. High-voltage cables will have a "memory" effect under DC voltage, storing and accumulating unipolar residual charges. Once there is "memory" caused by the DC withstand voltage test, it takes a long time to release this DC bias. If the cable is put into operation before the DC residual charge is completely released, the DC bias will be superimposed on the peak value of the power frequency voltage, making the voltage value of the cable far exceed its rated voltage, which may cause cable insulation breakdown.

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3. During the DC withstand voltage test, wire and cable manufacturers will inject electrons into the polymer medium to form a space charge, which will reduce the electric field strength there, making it difficult for breakdown to occur. High-voltage cables are prone to generate space charges at semiconductor protrusions and dirt spots. However, if a surface flashover or cable accessory breakdown occurs during the test of the cable terminal, wave oscillations will occur on the cable core. At the place where space charge has accumulated, the polarity of the oscillating voltage quickly changes to a different polarity, making the The electric field strength at the place increases significantly, which may damage the insulation and cause multiple clicks.


4. One of the fatal weaknesses of high-voltage cables is that it is easy to produce water branches in the insulation. Once the water branches are generated, they will quickly turn into electric branches under DC voltage and form a discharge, which accelerates the insulation degradation, so that it will be affected by power frequency voltage after operation Down to form a breakdown. The simple water branch can still maintain a considerable withstand voltage under AC working voltage, and it can be maintained for a period of time.

Life safety is above all else. Because of its unique advantages, high-voltage and low-voltage fire-resistant cables are widely used in high-rise buildings, underground railways, underground streets, large power stations, and important industrial and mining enterprises. We believe there will be fewer accidents caused by cable problems.


URL of this article: http://herzheart.com/南方双彩网/399.html

Keywords: wire and cable manufacturers , Zhengzhou wire and cable , Henan wire and cable

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