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Cable Testing and Fault Locating at Wind Farms … Part III

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Cable testing on new installations …

Since the cable has been tested at the factory prior to delivery, new installations typically only require localized testing.  The area most prone to installation defects are the cable sheath, splices and terminations.

After installation the sheath test is the first test which should be performed.  This test will indicate whether there has been any mechanical damage to the outer cable sheath.  If there has been damage to the sheath the degradation of the neutral and the cable insulation will be imminent which will result in premature cable failure.  The test is performed by applying a test voltage onto the cable’s neutral.  If the sheath is intact and not damaged the neutral will hold the voltage and show no leakage current.  If there is damage to the sheath the voltage will drop and there will be current leakage to earth.  The location of the sheath fault can be accomplished through the use of an earth fault locator.

After the sheath integrity has been validated the integrity of the splices and terminations can be tested by applying a VLF Hipot test.  VLF or Very Low Frequency testing is done to prevent an in-service cable failure and serves as a pass/fail proof test.  Additional diagnostic value can be obtained by connecting a Tan Delta system to the VLF Hipot.  Now the tan delta of the cable can be quickly measured and the results stored thus providing a “signature” of the cable being tested.

Cable testing of existing or service aged systems …

When testing involves existing systems, particularly service aged systems, the condition of the cable itself along with the splices and terminations become of interest.  By testing the collector cabling the owner can proactively manage the cabling system, thereby avoiding costly emergency outages.

A VLF Hipot can be applied to a service aged cable which may have developed water trees or electrical trees; the VLF will test the entire cable and can be used to drive the weakest location on the cable to failure, thus allow a planned fault and locate.  If the VLF Hipot is connected to a Tan Delta system the test can now offer diagnostic value and enable the cable test engineer to detect insulation defects or aging characteristics before the cable fails in service.

Talk with the application experts at Protec Equipment Resources.  We understand underground cabling and the various testing and fault locating methods required to maintain healthy and reliable systems.  We also maintain the most complete rental inventory of preventative and predictive test equipment including insulation resistance testers, DC Hipots and VLF Hipots, and Tan Delta testers from leading manufactures.  Manufacturers such as Megger, Metrel, High Voltage Incorporated and HV Diagnostics.