High Voltage DC Test is Killer for XLPE Insulated Power Cable

Fig- Formation of Electric Tree on XLPE Cable Insulation

High Voltage DC Test is Killer for XLPE Insulated Power Cable

The high-voltage DC (Direct Current) test carry out actually confirm the cable is capable to take the pressure. AC (Alternating Current) test instate of DC test can do if anyone interested. The problem is AC high voltage arrangement at the site is not physible to do. 

In operating conditions cables will operate the AC system, so AC high voltage test is no problem for it, rather AC is better than DC. Repeating the DC high voltage test may internal injure the cable that may cause cable failure in the future.

Why High Voltage DC Test is Danger for XLPE Insulated Power Cable?

The high voltage DC test is alternately referred to as the Hi-Po test. The high voltage DC (Direct Current)  testing method is performed for a long time on cable insulation systems, especially for field tests which are broadly known as SAT (Site Acceptance Test) for users and contractors. 

But recent research has shown that DC testing is the cause of 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 why 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 covers voltage levels above 5 kV.

Type of DC Hi-Po Test:

DC Withstand Test: DC withstand test is a Hi-Po test where the voltage at a prescribed level is applied for a prescribed duration. The cable system will be considered acceptable if no breakdown occurs.

Leakage Current Tests: 

The leakage current test is a Hi-Po test with the function of time where the 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 which presents the diagnostic information of the cable system.

Voltage Test: 

The voltage test is also known as Leakage Current Tip-up Test 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 whether the insulation system is defective or not.

Weak Points of DC Hi-Po test for Power Cable:

• This test is blind to certain types of defects, such as clean voids and cuts. 
• May not replicate the stress distribution existing with power frequency ac voltage. The stress distribution is sensitive to temperature and temperature distribution.
• May cause undesirable space charge accumulation, especially at accessory cable insulation interfaces.
• May adversely affect the future performance of water-tree-affected extruded dielectric cables.

Though the DC Hi-Po test is simple and easy recently experts are thinking DC high voltage test keeps some signs that bring bad effects for cable at age. Consequently, we can say the above-mentioned disadvantages of the DC Hi-Po test turn themselves into a killer for XLPE insulated power cable.