guangxi cable news: discuss the problem of dc withstand voltage test of high voltage cable-非凡电子娱乐

with the national "west to east", "south north" project to promote,

high voltage direct current cable will be used as the main force.

the large-scale access of new energy and the construction of urban transmission cable,

high voltage direct current cable.

high voltage dc cable is the only means of transmission of offshore wind, sea island.

high voltage and ultra high voltage cable has become an indispensable material in modern urban power grid project,

however, china's high voltage ehv cable field started late,

materials, equipment and manufacturing technologies have long been heavily dependent on introduction and imitation.

here we talk about the high-voltage cable dc withstand voltage test problems mainly in what areas?

1 under dc voltage, the electric field distribution of the cable insulation depends on the volume resistivity of the material,

the electric field distribution under ac voltage depends on the dielectric constant of the medium,

the distribution of dc electric field strength and the distribution of ac electric field intensity are different in the cable accessories such as joint box,

the mechanism of insulation aging under dc voltage is different from that under ac voltage.

therefore, the dc withstand voltage test can not simulate the operation condition of high voltage cable.

2 high voltage cable will produce the "memory" effect under the dc voltage,

accumulation of unipolar charge. because of the "memory" caused by the dc voltage withstand test",

it takes a long time to release the dc bias.

the cable is put into operation if the dc residual charge is not fully released,

dc bias will be superimposed on the peak of the power frequency voltage,

so that the voltage on the cable far exceeds its rated voltage,

cable insulation breakdown.

3 dc voltage withstand test, there will be electronic injection into the polymer medium,

the formation of space charge, so that the electric field intensity is reduced, which is difficult to breakdown.

the space charge of the high voltage cable is easy to be generated from the source and the pollution point.

however, in the case of cable terminations, surface flashover or cable attachment breakdown occurs,

will cause the cable core line to produce wave oscillation in the space charge has accumulated space,

due to the polarity of the oscillation voltage, the polarity is changed rapidly,

so that the electric field intensity increased significantly, may damage the insulation, resulting in multi click through.

4 fatal weakness of high voltage cable is easy to produce water branch,

once a water branch is generated, it will change into an electrical branch and form a discharge at the dc voltage,

accelerate the deterioration of insulation, so that the operation of the power frequency voltage in the formation of breakdown.

the pure water branch in the ac voltage can maintain a considerable pressure value, and can maintain a period of time.

life safety is higher than all, high voltage and low voltage fire-resistant cable because of its unique advantages in high-rise buildings, underground railway,

underground street, large power plants and important industrial and mining enterprises and other places related to fire safety and fire rescue are widely used.

we believe that there will be fewer and fewer accidents caused by cable,