Defect Blog

Each year, millions of people and thousands of businesses are impacted by underground cable system failures. IMCORP is dedicated to advancing the understanding of how these failures occur and more importantly, how they can be avoided.

Jun 09 2017

Termination Damaged but Passed by VLF Test

By: Ben Lanz and Bill Corrente

Posted in: Workmanship, Wind, Utility, Solar, Renewable, Generation


Termination Damaged but Passed by VLF Test
Our utility client asked us to commission cable systems at a new generation facility after experiencing several termination failures.  The installation contractor had already tested the cable systems with a very low frequency (VLF) test. Uninformed contractors often make a claim based on a common myth that ‘proper’ VLF testing would detect serious cable defects while not harming healthy insulation or aggravating minor defects.  In addition, the claim often states that passing a VLF test means the cable system will deliver years of trouble free service.  Unfortunately the owner initially believed these myths, energized the system and subsequently experience several catastrophic failures that damaged switchgear, costing them significant down time and losses in generation revenue.  The IMCORP Factory Grade® technology pinpointed dozens of terminations that did not meet the accessory manufacturer’s minimum performance standards.  When the terminations were dissected the technician not only found workmanship issues, including insufficient shrinkage of heat shrink layers, but clear evidence of damage caused by the VLF test that passed the terminations a short time before.  

The long, narrow interfacial tracking visible once the outer termination layer was removed (see picture above) is typical of VLF test induced damage.  This termination most likely would have failed within a short time in service causing yet more down time and losses in generation revenue.

 To learn more about Factory Grade technology and how to ensure critical cable system reliability Contact us