During the third of three annual visits to survey the critical UPS-backed equipment on site we detected an ultrasonic emission on a section of one of the critical rising busbars. In total we had listened to 187 sections of busbar with the ultrasonic stethoscope probe. This section stood out as having an unusual sound signature that warranted further investigation.

PROCESS
As the emission was within a section busbar it was important to ensure that it was not a reflection from any other source of ultrasound in the switchroom. Support brackets were loosened or removed to rule out sympathetic vibration from plant that may have been transmitting along brackets and barriers were used to isolate any external influences. Ultrasound recordings were taken with the stethoscope contact module and analysed along with comparative recordings from similar ‘healthy’ equipment using identical settings on our analysis software.

REPORT
The analysis revealed that the emissions were tracking events caused by internal insulation breakdown and if left uncorrected would have been very likely to result in failure of the busbar. The site staff were notified and the decision was made to transfer the load to the alternate supply that evening. A programme of regular monitoring was put in place to trend the issue while a new section of busbar was ordered.

REMEDIAL WORKS
By transferring the load it was possible to reduce the likelihood of a failure of the busbar and we were able to have a new section manufactured and delivered to site. During a weekend shutdown we were able to replace the faulty section of busbar, along with the internal joint components either side of the fault. Insulation and resistance test were then completed and the busbar was then put back into service as the primary supply to the UPS equipment.

CONCLUSION
As this was the third time we had surveyed this busbar system it was clear that the fault had developed since our last visit. Early detection of the insulation breakdown allowed a controlled replacement to be carried out at a more convenient shutdown. When equipment such as this, which is made to order, fails it is not only the immediate outage and disruption that is a problem but the possibility of being without a component for some months while one is located, ordered or manufactured.