ABB’s Computed Radiography service saves time and money on HV switchgear inspection
8 December 2015
New inspection service is based on leading edge technology that provides high resolution x-ray images of critical power network assets in digital format
ABB’s UK Service Team is now offering an advanced x-ray technique that takes non-invasive inspection of critical power network assets to the next level. Known as Computed Radiography (CR), this technique makes it possible for service engineers to see inside high-voltage (HV) switchgear without having to disassemble it, reducing outages from days to hours. In many cases switchgear can remain live and even in service while the inspection takes place.
The importance of HV switchgear in electrical networks requires utilities and industry 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. Previously, the only sure way to make these vital checks was to take the switchgear apart. And when dealing with breakers filled with SF6 gas there is the added complication that they must be degassed and the SF6 collected and stored for refilling or recycled.
CR provides a leap forward in technology that enables digital x-ray images to be produced without the use of expensive and delicate film. The process uses the same x-ray source as for film (x-ray tube, Iridium or Cobalt, Linear Accelerator and so on) and the image is captured on a flexible, re-usable sheet coated with a phosphor material called an imaging plate. Following exposure, the plate is scanned by laser to secure a permanent non- degrading digital image. This image can be enhanced, filtered, annotated, zoomed, scaled, shared and stored.
The CR setup is assembled around the equipment, eliminating the need to disassemble or move it. The reusable plate is normally attached to the switchgear and a reference object is arranged in the same plane to provide scale. To protect workers from radiation, the area is evacuated during the exposure. After exposure, the screen is scanned and subsequently cleaned for reuse. No latent radiation remains after the process, all equipment and areas are completely safe for immediate access.
A major advantage of CR is that no darkroom, water or chemicals are required and the equipment only requires a standard low voltage power supply. This makes the inspection easier to perform on site as well as offering a significant reduction in time and cost per exposure. The image processing time is decreased from over eight minutes to less than one minute. The digital image on a high resolution screen can be interpreted, marked and annotated using mouse/keyboard instead of a grease pencil.
ABB can perform CR on both its own equipment and on that supplied by other OEM and legacy manufacturers. Most importantly, its service team has the expertise to evaluate the images and provide the appropriate service advice.
Combined with operational diagnostics (such as timing tests and dynamic resistance measurements), computed 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 CR images to measure parts that are subject to wear such as comparing uneven ablation on electrical contacts. As well as wear problems, it can also reveal manufacturing or installation defects. Whole fleet assessments can be undertaken to provide a wide-angle view of a particular asset type, these assessments can include identification of latent defects.
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 CR 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 CR inspection 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 CR 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.
For more information, please contact:
ABB Power Products & Power Systems Divisions UK
Tel: +44 1785 825050