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UPS Busbar Joint Failure

Metropolitan TEGG was initially called out to site after a fault developed on one of our customers UPS distribution busbars. Voltage on the L2 phase dipped on multiple occasions causing the static transfer switches to transfer to the non-essential supply. We recommended and carried out power quality monitoring for a period of six weeks.

Results proved to be inconclusive as no events occurred during the monitoring period.

At the next available shutdown Metropolitan TEGG performed ductor testing on the UPS busbar which highlighted L2 as having greatly elevated readings. Energised thermal imaging and ultrasonic testing was the next step. As part of the TEGG procedure each busbar joint was given a unique ID label to allow each asset to be traced through our software and to serve as a target to give accurate temperatures. Baseline infrared and digital images and a fifteen second ultrasonic sound file of each joint were recorded for analysis. During our inspection a thermal anomaly of around eight degrees was detected across the span of a three metre length of busbar with a surface temperature of only thirty four degrees. This anomaly was recorded and included within the TEGG report issued to the customer. On the next routine building shutdown we suggested and performed ductor tests across each of the joints and recorded the results.

A mid point of the busbar was selected as a starting point for up and down-stream tests. The objective was to determine which joint/ joints had an increase resistance. On removal of the thermally abnormal joint cover severe discolouration was seen on both the L2 and L3 conductors. It was evident that the connection had been failing for some time and had seen arcing temperatures severe enough to fuse the conductors together. The damage seen at the joint was likely to have been caused by either contamination of the joint faces when the joint was tightened or an incorrectly torqued joint bolt. Since this issue has been uncovered a plan has been put in place to replace the lengths of busbar either side of the joint. Busbar manufactures suggest at the very least to carry out annual visual inspections.

In most cases a shutdown for visual inspection is not possible, however carrying out energised non-intrusive thermal and ultrasonic inspections of your busbar system could prevent or help detect joint failures at the early stages lessening the risk of downtime and damage to ancillary equipment should a failure occur.