Seeing inside switchgear

ABB Field Service Engineer Jerry Michaelson explains how radiographic inspection saves costs and downtime and enables better maintenance planning – based on an original paper published in ABB Review, 2012.
The traditional method of inspecting switchgear is far from simple. First, downtime has to be planned and co-ordinated. Before you approach the equipment, it must be disconnected and earthed. Breakers filled with SF6 have to be degassed (and because SF6 is a potent greenhouse gas, it must not be released into the atmosphere but collected and recycled). Then begins the actual dismantling and subsequent reassembly. This phase brings the risk of introducing defects that were not previously present. Parts can be lost, damaged or incorrectly fitted and debris can enter the equipment. Disassembly for inspection is time consuming and costly, and not always effective.

However, the importance of switchgear in electrical networks requires utilities to carry out regular inspections to avoid the risk of unexpected malfunctions and loss of supply. At the same time, detailed knowledge of its internal condition helps the effective planning of maintenance and replacement schedules.
With radiographic inspection, we can now see inside equipment without having to disassemble it. The switchgear still needs to be taken out of service, disconnected and earthed. But the subsequent steps and overall downtime are replaced
by the far simpler and much less invasive use of radiography equipment - reducing downtime from days to hours.
As an X-ray source, we use a natural source of radiation. The X-ray setup is assembled around the equipment, eliminating the need to disassemble or move any of it. The plate is normally attached to the switchgear and a reference object is arranged in the same plane as an indicator of size. To protect workers from the radiation, the area is evacuated during the exposure. After exposure, the screen is scanned and subsequently cleaned for reuse.
ABB can perform radiography on both our own equipment and on that supplied by other OEM and legacy manufacturers. Most importantly, we have the expertise to evaluate the images and provide the appropriate service advice.
Combined with operational diagnostics (such as precise measurement of response times to assess the degree of contact wear), radiography provides a low-cost yet effective way of obtaining detailed information on the condition of equipment. This helps to predict the remaining number of operating cycles before intervention is required.
Experts can use such radiographic images to measure parts that are subject to wear such as comparing an ‘in spec’ nozzle with an ‘out of spec’ one. As well as wear problems, we can also reveal manufacturing defects such as detached screws and incorrectly inserted bolts.

Detached screw revealed by radiography
Case study: Call Henry Inc. and NASA
Call Henry Inc. is the high-voltage on-site service contractor at the NASA Glenn Research Center in Cleveland, Ohio in the United States. The reliability of the power supply is vital for the center’s operations. A review of the switchgear revealed that many
of the center’s circuit breakers were 10 to 14 years old, with one having completed 2,700 operations during its lifetime.
ABB was called in to carry out external diagnostic testing and radiography of 26 SF6-filled circuit breakers. The tests showed that, of the 26 breakers examined:
– one required entry to remedy a hardware problem
– seven required reduction of the SF6 gas moisture content
– 19 were spared entry and intrusive maintenance.

Overall, 38 man-days of intensive, internal inspections were saved with NASA’s switchgear fleet restored to reliable operating status for less than 50 percent of the cost of traditional maintenance.

Case study: Pacific Northwest utility
ABB was asked to perform radiographic inspections of eight ABB breakers for a Pacific Northwest utility. Shortly before the inspection, the utility had removed a Westinghouse breaker from service. Inspection showed that the nozzle on one contact was broken and the guide rings from four others had become detached and were lying at the bottom of the tank. This situation posed the possibility of a catastrophic circuit breaker failure. Increasing the risk was the fact that the broken part turned out not to be an OEM component but a reverse-engineered non-OEM one.
Five further breakers of the same design were then inspected. Based on the findings and a review by a Westinghouse expert, it was determined that one of these breakers had no less than three broken nozzles. One phase was missing both nozzles and one phase was missing one. If this breaker were called on to perform a full-fault interruption, a failure would be likely. The other breakers were found not to be in need of immediate repair. This operation saved the customer £36,000 compared with traditional internal inspections.

Radiography is the time and money saving tool
These case studies, and many other examples, show that radiographic inspection saves both time and money, both by reducing the amount of work needing to be done when compared with traditional invasive inspection, and in terms of customer disruption and downtime.