Why Need Power Cable Test After Installation

Power Cable Test After Installation

HV/EHV power cable testing in the field after installation is a common requirement for cable users. Meanwhile, MV-normal voltage, HV-high voltage, and EHV-extra high voltage power cables are carefully tested by the manufacturer before consignment with AC-alternating or DC-direct voltage. 

Some defects may not be detected or, more likely, damage may occur during shipment handling, carrying to storage and site, or during installation. To make sure additional testing is carried out after installation and prior to being placed in service, including joints and terminations, may be conducted. 

Moreover, many users find that gradually cable systems degrade and service failures become troublesome for them. Due to that, they desire to reduce or eliminate those failures by performing periodic tests after some time in service. To determine the economic replacement of the downgraded cable, users need a special diagnostic test.

Power cable tests in the  field after installation may be broadly divided into the following two categories:

A.   Field tests are intended to detect defects in the insulation of a cable system in order to improve service reliability after the defective part is removed and appropriate repairs performed. These tests are usually achieved by the application of relatively elevated voltages across the insulation for the prescribed duration.

B.   Field tests are intended to provide indications that the insulation system has deteriorated. Some of these tests will show the overall condition of a cable system and others will indicate the locations of discrete defects which may cause the sites of future service failures.  Both varieties of such tests may be categorized as “pass/fail” or “go/no-go” and are usually performed by means of moderately elevated voltages applied for a relatively short duration, or by means of low voltages.

Applied Voltage Type for Cable Test:

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Both Direct Current Voltage and Alternating Current Voltage have been accepted for many years as the standard method.

DC test for Power Cable: 

DC testing method is performed for a long time as high voltage tests on cable insulation systems, especially for a field test. However 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 water trees.

AC test for Power Cable: 

Alternating voltage tests at alternating voltages are highly acceptable since the insulation is stressed in a similar way to normal operation and the test is similar to that used in the factory on new reels of cable. However high voltage AC test equipment normally has heavy, bulky, and expensive test transformers which may not be readily transportable to a field site.

During high voltage tests carried out of the power cable on site after installation, the grounding system should be sufficient, due to long periods of time following such tests can experience dangerous charge build-ups and cause an accident. To avoid any mistake recommended grounding procedure and appropriate working rules should be followed.