Thermal imaging and ultrasonic testing are important tools in your PM program.
A well-executed preventative maintenance program is the cornerstone of every plant’s asset management strategy. Ensuring that equipment is regularly serviced and tested helps mitigate the likelihood of an unexpected failure and associated downtime. While a number of plant systems and equipment will show telltale signs when maintenance is required, such as dirty filters, squeaky belts or visual alarms, electrical equipment is often assumed to be in good working order, as operational issues may not be readily apparent. If left uncorrected, minor issues can persist, damaging equipment and resulting in service interruptions. Fortunately for plant managers, there are two easy-to-use, cost-effective diagnostic tools that should be incorporated into every electrical preventative maintenance program: thermal imaging and ultrasonic testing.
Over the past decade, thermal imaging has seen significant market penetration in maintenance and service industries. The first commercial thermal imaging cameras dated back to the 1980s and utilized liquid nitrogen (LN2) cooling for the infrared detectors. The cooling system was necessary to ensure that the internal detectors were not biased by heat produced within the camera’s electronics. This resulted in a large device that was both cumbersome and expensive to operate. Consequently, thermal inspections of electrical power systems were not performed very often and were confined to facilities that could afford the expense. With the exponential growth of the digital industry, thermal imaging detectors were upgraded with electronics that do not require the need for cooling and, as a result, cameras decreased in size and cost. Today’s thermal imaging cameras are analogous to regular digital cameras, however, instead of relying on electromagnetic radiation in the visible light spectrum (400nm – 700nm) to produce a photograph, they sense radiated heat in the infrared spectrum (700nm – 1mm). Changes in infrared radiation produce a corresponding change in voltage, current or resistance, within the imager, and this is converted into a visible image, through digital signal processing.
A multitude of thermal imaging cameras are available in today’s market, with models ranging from the size of smartphone to about the size of a video camera. Different camera models will have varying performance criteria, which include: temperature range, detector resolution, field of view, focus/zoom options and accuracy. Cameras offer a variety of image processing features, such as different colour palettes; recording infrared photos and corresponding digital photos with the same image capture, to avoid the need of having a separate digital camera; and hybrid images, which incorporate thermal blending/fusion between visible and infrared images, to make identification easier when compared to straight IR images. Digital images are typically stored on a removable, secure digital (SD) memory card, or on a camera’s onboard memory, which is accessible via Micro-USB. Software is often included with the purchase of a thermal imager and can help users create inspection reports, with images recorded on site. Other notable camera features include wireless connectivity for data transfer, impact resistance to withstand inadvertent drops and enclosure ratings to protect against water spray and the elements. Thermal imaging cameras range in price from $2,000-$10,000, for base models, to upwards of $20,000 for more specialized models. For the purposes of inspecting electrical power distribution equipment within a plant environment, a base model camera should be more than sufficient.
Before undertaking a thermal inspection of electrical equipment, an important factor to consider is if sufficient electrical load will be present on the system. Thermal energy (“heat”) within a power system is proportional to the load (current or Amps) and resistance in the system. Inspection work needs to be performed while plant equipment is operational, to ensure meaningful results are recorded. When inspecting equipment, the primary source of concern is “loose” connections, or high impedance connections. Predominantly caused by the thermal expansion and contraction of materials, loose connections are typically found in equipment lugs, where wires/cables terminate onto a circuit breaker or disconnect switch, fuseholders, joints and terminations on bus work (switchboards, switchgear and bus duct systems) and cable splices. Although aluminum conductors are widely used and are a cost-effective alternative to copper, attention should be given to the inherent properties of aluminum, which can result in loose connections. Aluminum conductors require the use of dual-rated terminations (Cu-Al), to mitigate the effect of “cold flow” and varying coefficients of expansion and contraction; and can be subject to the buildup of aluminum oxide (a by-product of the oxidation of aluminum), which can greatly increase the electrical resistance of a circuit. If left uncorrected, high impedance connection can result in equipment damage, premature failure and can create a fire risk. Thermal imaging can also help to speedily diagnose other common issues, including load imbalances, overloaded circuits, blown fuses, verifying that a heat tracing circuit is operational and motor overheating.
Larger plants will typically utilize medium voltage power distribution systems (5-15kV or higher), given the greater physical footprint and distributed concentrations of electrical loads. With higher operating voltages, medium voltage equipment can be subject to additional destructive phenomena over time, which can result in insulation breakdown, leading to flashovers and premature equipment failure. Partial discharges, corona and tracking are caused by the localized dielectric breakdown of insulating materials, typically resulting from voids, treeing or defects in the insulation. Ultrasonic testing provides a means of detecting ultrasounds produced by partial discharges, arcing, etc. An ultrasonic tester consists of a sensor (parabolic dish or cone), a detector and amplifier to translate the emitted ultrasounds to the audible range. A coarse buzzing or grinding sound, will be audible when an issue is present. Although there are fewer manufacturers of ultrasonic test kits, products are available from brand-name suppliers and costs are comparable to a base model thermal imager. Ultrasonic testing can also be used to perform safety checks for signs of arcing in low-voltage equipment, prior to opening covers for a thermal inspection, and can help diagnose issues with mechanical systems in a plant, including motor bearings, compressors and pressurized gas systems.
After researching available equipment options, plant managers are faced with the question of what is the most cost-effective way to implement thermal and ultrasonic inspections. Personnel must be trained in the use of test equipment, they require an understanding of power distribution systems and potential issues, and they have to observe workplace safety and personal protective equipment requirements. It is important to document inspection results in a proper report format since they will serve as a comparison for future inspection work, and in the event of an unexpected failure, insurance companies may ask to review maintenance records. Test equipment should be periodically recalibrated to ensure accurate results and a secure storage space is advisable to prevent theft. Given these factors, employee turnover and that maintenance personnel are often inundated with ongoing work orders, it is often more cost-effective to retain a contract service provider to complete inspection work.
There are several important considerations to take into account when procuring inspection services. The service provider should have significant experience with electrical power systems and performing thermal and ultrasonic inspections. Familiarity with how electrical equipment is installed and maintained, as well as applicable codes and standards, such as the Canadian Electrical Code, NFPA and IEEE, should be an important qualification. Finally, quality of service and the quality of deliverables, such as reports and meaningful recommendations, should not be sacrificed for the lowest cost.
Thermal inspections and ultrasonic testing of electrical power systems should be incorporated into your plant’s preventative maintenance program. Industry standards and property insurance companies recommend performing inspections on an annual basis, at a minimum. The frequency of inspections should be increased to semi-annual or quarterly, where warranted by loss experience or changes in electrical loads or operating conditions. Infrared inspection windows provide a proactive means of encouraging thermal inspections and make the process safer, by eliminating the need to open access doors and reducing the risk of working around a live source. IR windows should be installed on all new applicable equipment and can be retroactively installed on existing equipment. Windows should be situated to provide a clear view of cables terminating on bus work and cables terminating in circuit breakers. Whether you choose to perform inspection work in-house or contract a service provider, installing windows will provide ease of access and reduce inspection time and costs. By including these two diagnostic tests in your facility’s operating budget, you can proactively detect operational issues in your electrical power systems, minimize unexpected downtime and maintain important records of ongoing maintenance.
Michael Holdsworth, C.Tech., has enjoyed a career spanning more than 50 years in engineering, construction and facility operations. In his current role as senior technical manager at C2C Enertec Inc., Mike helps facility operators and plant managers implement preventative maintenance programs for their electrical power systems. He can be reached at firstname.lastname@example.org.
Philip Chow, P.Eng., P.E., is a senior project manager and electrical engineer specializing in electrical infrastructure projects and construction in mission critical facilities. He can be reached at Philip.Chow@hhangus.com.