High Voltage DC Test is Killer for XLPE Insulated Power Cable
High Voltage DC test is alternately referred as Hi-Po test. High voltage DC (Direct Current) testing method is performing for long time on cable insulation systems, especially for field test which broadly known as SAT (Site Acceptance Test) for users and contractors . But recent research has shown that DC testing is the causes to certain types of defects and that it can make worse the deteriorated condition of some aged cables insulated with extruded dielectrics and affected with electrical-tree and water-tree. That’s way our article question “Is High Voltage DC Test Killer for XLPE Insulated Cable”.
LVDC or Low voltage DC testing is covering voltages up to 5 kV and HVDC high voltage dc testing covering voltage levels above 5 kV.
Type of DC Hi-Po Test:
DC Withstand Test: DC withstand test is such a Hi-Po test where voltage at a prescribed level is applied for a prescribed duration. The cable system will be considered to acceptable if no breakdown occurs.
Leakage Current Tests: Leakage current test is a Hi-Po test with function of time where total apparent leakage output current is recorded to a prescribed voltage level. Not the absolute value, but the variations of leakage current with time is recorded what presents the diagnostic information of the cable system.
Voltage Test: Voltage test is also known as Leakage Current Tip-up Tests where voltage is increased in small steps while the steady-state leakage current is recorded, until the maximum test voltage is reached. The relationship graph between current and voltage denotes the insulation system is defective or not.
Weak Points of DC Hi-Po test for Power Cable:
A. This test is blind to certain types of defects, such as clean voids and cuts.
B. May not replicate the stress distribution existing with power frequency ac voltage. The stress distribution is sensitive to temperature and temperature distribution.
C.May cause undesirable space charge accumulation, especially at accessory cable insulation interfaces.
D.May adversely affect future performance of water-tree affected extruded dielectric cables.
Though DC Hi-Po test is simple and easy recently experts are thinking DC high voltage test is keeps some signs that bring bad effect for cable at aged. Consequently we can say above mentioned disadvantages of DC Hi-Po test turn itself as a killer for XLPE insulated power cable.