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Transmission Cable Diagnostic Testing after Multiple Failures

Expert Capabilities for In-Depth Accurate Test Results

Project Background

A utility located in the United States installed a cable system in 2008. With the acceptance of the cable manufacturer, the cable owner performed a soak commissioning test in compliance with IEC 60840 standards.
One year after successful completion of the commissioning test, one of the joints failed during operation. The joint failure was dismissed as a manufacturing or installation defect. The joint was replaced and the cable system was successfully retested using VLF (Very Low Frequency) at 0.1 Hz and 2Uo equivalent to 80 kV for 15 minutes. 
Two years later, another joint in the same vault failed during operation. The joint was again replaced and failure was deemed to have been due to an installation defect. In 2014, the joint replaced in 2009 failed again, prompting the cable owner to question the integrity of the cable system.
Scope of Work
In early 2016, Kinectrics was called in to perform in-depth diagnostic testing on the utility’s cable system to determine the integrity of the remaining joints and cable sections. Our test engineers performed a jacket integrity test on the three cables and localized the compromised section using a 10 kV DC power supply.
Kinectrics also performed AC Hi-Pot testing at 56 kV and a natural frequency of 69 Hz for 60 minutes using our trailer-mounted Resonance Test System (RTS).  During the resonance testing, Partial Discharge (PD) was monitored on all accessories and it was determined that two additional joints had significant partial discharge and thus failed the PD test.
Test Results
Kinectrics’ recommendations were to replace the compromised cable section due to the failed jacket and replace the two joints that exhibited PD activity at near operating voltage.
The combined AC Hi-Pot testing at 1.4Uo to 1.7Uo with Partial Discharge diagnostic testing provided our engineers with accurate test results in compliance with IEC 60840 standards. In turn, our client acquired a higher level of confidence in the overall health of the installation quality of the cable system. 
The utility is currently replacing the compromised cable section and faulty joints following our recommendations.  Kinectrics is awaiting completion of the repairs to perform the commissioning and jacket integrity testing on the newly- replaced cable section and accessories.