CM Technologies Corp Successfully Troubleshoots 4 kV Festoon Cable at the APM Terminals’ Facility in Elizabeth, NJ
The Crane Manager at APM Terminals’ Elizabeth, New Jersey facility reported a complete failure of 4 kV festoon cable on Crane #4 in December 2013. The crane was forced to shut down until the problem was resolved, limiting the shipyard’s ability to load and unload boats. A damaged wire causing a short circuit was believed to be the culprit. After three months of downtime spent troubleshooting the problem, CM Technologies was called to track down the fault.
The cables running up to the drive mechanism consist of three (3) individually shielded #6 conductors and a separate ground conductor (see above); they are manufactured by Anixter. The cables are each approximately 200 feet long and were believed to be part of the original crane installation, meaning they have been in service for over 40 years.
Some insulation resistance testing and troubleshooting was performed prior to CM Technologies’ visit. The result of this effort suggested that two (2) of the three (3) conductors were open-circuited, but the third conductor was intact.
On December 6, 2013, CM Technologies performed TDR testing on the failed cable from two test locations. The first tests occurred at junction box in the primary shop housing, where the cable from circuit breaker and the festoon cable are terminated. The festoon cable conductors were completely isolated from the terminal block, but the ground conductors were left terminated to junction box (i.e., grounded).
Testing was conducted between each phase-to-phase combination and between each phase and ground. The other end of the festoon cable had all of the conductors shorted together and clamped to ground.
The first anomaly was observed when resistance tests indicated open circuits (>30 MΩ) between each conductor and ground and between the conductor to conductor tests. The resistance should have been significantly smaller: less than 5Ω for this type of cable.
All of the phase-to-phase and phase-to-ground TDR signatures indicated an open circuit approximately 18 to 20 feet (5.75 meters) from the junction box location. The figure below shows the signature acquired between phase A and ground, pinpointing the break in the cable.
Testing was then performed from the other end of the festoon cable. Again, all of the phase-to-phase and phase-to-ground TDR signatures indicated an open circuit approximately 190 to 200 feet from this junction box location. The figure below shows the signature acquired between phase A and ground, indicating the same break in the cable.
It took less than 3 hours to perform the testing, analysis and for maintenance personnel to inspect the cable, finding a severely damaged section approximately 20 feet from primary junction. All three conductors had been open-circuited; see below for the approximate location.
The cable was replaced in March 2014. CM Technologies conducted a post-installation test to ensure fault-free operation.
Article and photos by Greg Allan, CM Technologies.