High voltage cable testing
DC voltage test: 
 
Its merits are: test equipment has small capacity, small volume, convenient operation and carrying, especially suitable for field test, in oil paper insulation cable application is successful, international and national standards have clearly defined. And the XLPE cable for DC voltage test has the following shortcomings:
 
(1) DC voltage withstand test can not simulate the running conditions of XLPE cables.
 
(2) the "memory" effect can be produced by the XLPE cable under the DC voltage, and the accumulation of unipolar residual charge is stored. If in the cable in the DC residual charge is not fully released before put into operation, DC bias will superposition in the power frequency voltage peak, making cable voltage value exceeds its rated voltage, which may lead to the breakdown of cable insulation.
 
(3) DC voltage, electron injection into the interior of the polymer medium, formation of space charge, the electric field strength decreased, XLPE cable semiconductor convex source and pollution, easy to produce the space charge, which difficult to find defects. At the same time, if the external dust flashover or cable accessories breakdown, the space charge accumulation place, due to the oscillation, voltage change rapidly for the opposite polarity, the electric field intensity increases significantly, may damage to insulation, click on the perforation caused.
 
(4) XLPE cable fatal weakness is the internal insulation is easy to produce water, under DC voltage will rapidly changing electrical tree, and the formation of discharge, accelerated the deterioration of insulation; and pure water tree under AC voltage can keep considerable pressure value, and can keep the time.
 
(5) the research and practice both at home and abroad show that the DC voltage test can not effectively detect the defects of the AC voltage,
 
In short, XLPE high voltage plastic insulated cables for DC voltage test has reached a consensus at home and abroad.

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