Cable Testing and Fault Locating at Wind Farms … Part I

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Since the underground cabling serves as the backbone of the wind farm collector system testing the integrity and condition of the cabling is critical in ensuring reliability of the entire system.  Over the years there have been several methods and/or philosophies regarding the testing of underground electrical power cable. The Insulated Conductor Committee of the IEEE Power Society has divided these methods or philosophies into two categories, Type 1 Field Tests and Type 2 Field Tests.

Type 1 tests are intended to detect defects in the insulation of the cable system in order to improve the service reliability after the defective part is removed and appropriate repairs are performed. These tests are usually achieved by application of moderately increased voltages across the insulation for a prescribed duration. Such tests are categorized as pass/fail. Tests include DC (recommended for laminated cable systems; cautions and warnings for extruded systems), Very Low Frequency (VLF), Power Frequency Testing and Sheath Testing.

Type 2 tests are intended to provide indications that the insulation system has deteriorated, hence, are termed “diagnostic” tests. These tests include Tan Delta or Dissipation Factor Testing and Partial Discharge (PD) Testing.

Many cable failures are the result of installation practices of the underground cable.  Installation of cable systems includes trenching, cable pulling, clamping of cable, cable splicing as well as mounting of accessories.  High quality installation work performed by qualified field personnel is essential for achieving the low failure rates and reliability expected in wind farm collector systems. 

Testing of the cabling should be performed on new installations to identify localized problems which could have occurred during installation.  Testing should also be performed on existing cable systems.  Over time the cable can develop imperfections in the insulation.  By having a preventative maintenance testing program, defects in cable which were minor in nature when installed, but have gotten worse over time, will be detected before a costly emergency outage occurs.

Protec Equipment Resources understands underground cabling and the various testing and fault locating methods required to maintain healthy and reliable systems.  We maintain a 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.