UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

12.10.2018 | J. Bowen, W. Bauer, P. Anthony

“I truly believe that the common misunderstanding of cover use inhibiting thermography is a fundamental miss in understanding the basic concepts of thermography and the overrelianceon temperature criteria decision-making.” - Jay Bowen

UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

EXECUTIVE SUMMARYThis paper examines the potential to integrate two important means of preventative maintenance in electrical utility systems - bird and animal contact mitigation and infrared thermography. While the concept of reliable thermographic imagery of covered connections is conceptually valid, and practicably feasible, until now these two precautionary measures have ostensibly competing operational criteria.

With validation of this concept, electricity supply operators can develop training and field testing protocols, using quantitative and comparative methods that can provide actionable preventative maintenance data.

To this purpose we will be looking at a recent study, conducted by Bowen Infrared, which addresses the issue through a series of controlled experiments.

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

INTRODUCTIONThe essential goal of electrical utility preventative maintenance programs is to solve problems before they lead to safety concerns, unexpected downtime, and expensive outages.

Bird and animal contacts are one of the leading causes of electrical equipment failure and power outages for electrical utilities worldwide. Mitigation strategies safeguard both animals and electrical equipment. Contacts are preventable with properly fitted electrical component covers correctly installed during the life cycle of the equipment. Significant improvements to power system reliability can be achieved with the right protective cover-up.

Energy emissions that create anomalous hot spots in electrical systems are likely indicative of faulty connections or equipment failure. Infrared thermography is a diagnostic tool that measures surface thermal temperatures. It’s a non-contact method of viewing equipment which detects and displays IR data that may indicate equipment risks not evident to the naked eye.

These two forms of preventive maintenance programs have seemingly competing operational criteria. The cover’s primary function, to fully isolate contact points, creates an insulative barrier between the IR imager and the area being viewed.

If these preventative maintenance strategies could function together with a high level of confidence, electrical utilities could conceivably collect actionable data about operational fitness from thermographic imaging while mitigation covers are in place.

The following study, recently conducted by Bowen Infrared, addressed this issue. Through a series of controlled experiments, the study examined the potential efficacy and accuracy of thermographic imaging with mitigation covers in place over heated electrical connections.

THE STUDY The investigation was designed to determine if thermography is able to reliably detect the temperature of a connection point if it is under a cover, as well as how closely thermographic readings correspond to actual temperatures.

It further addressed the level of expertise needed to evaluate the thermography results, taking into consideration the variables in cover surface heat transfer. Finally, based on initial results, this report suggests options for testing and data collection in the field.

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

Methodology and TestingThe methodology Bowen used was to test infrared thermal imaging of bolted connections of common power system components under nine corresponding mitigation covers. The electrical components were placed under covers and heated to stable temperatures, enabling a comparison of the actual temperature to a thermal reading of IR emissions. A 500:1 thermal imaging camera was used, set back at 2.5 meters, and oriented straight at the cover. There were two test sets using different covers, which were first conducted in the lab, and then replicated in an outdoor setting.

THERMOGRAPHIC IMAGINGThermography registers differentials in energy emission in a target area and visualizes the data as heat temperature via the colour spectrum, spanning from pur-ple, blue and black (cooler temperatures) to yellow and white (hot). Infrared images are typically analyzed with reference to temperature decision scales, which provide mathematical standards for inferring actual heat measurement, and for unders-tanding deviations between expected and anomalous thermal readings.

Thermographic images can provide a great deal of data, but not an exact picture. As the research notes, even in optimum conditions gaining enough information from thermography to determine actual heat is very unlikely. It’s a complex task to get meaningful temperature data by testing power systems in the field, on energized electrical equipment, at normal-high load, and in typical operating conditions. Cover-up provides yet another challenge to thermography as a diagnostic tool.

FIGURE 1 Picture of a common bushing with a bolted electrical connection

FIGURE 2 Thermographic image of the connection without a cover heated to 43°C.

FIG. 1 FIG. 2

Example of Thermography Test Methodology

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

Test Set 1: Solid CoversThe first controlled set of tests studied heated connections under solid covers. Heat was applied to a bolted tang or tab, replicating various electrical connection configurations, and placed under four different solid covers. Using a controlled heat source, the connection temperature was increased in documented stages from 50°C to 250°C, allowing sufficient time between steps for all component temperatures to stabilize. The infrared emissions at each stage were recorded, and then compared to actual temperature data.

FIGURE 3 Vertical bushing cover 802

FIGURE 4 Thermographic image of the heated bolted connection with cover at 200°C. The image shows the hottest spots at the cable entry point and the area of the bolted connection.

FIG. 3 FIG. 4

Testing Solid Covers: Cover 802

FIGURES 5 & 6 Thermal imaging of a heated electrical connec-tion under a solid cover, with actual temperatures of 100°C (FIG. 5) and 200 °C (FIG. 6).

In both cases, the IR heat signature is visibly higher at the electrical connec-tion entry point and, most significantly, at the position of the heated connection.

FIG. 5 FIG. 6

Testing Solid Covers: Cover 3

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

FIGURE 7 This graph shows the temperature point correlation of the above thermal images. What can be taken from this controlled scenario is that there was an expected and corresponding increasein the hotspot temperature as the actual temperature was increased. Based upon heat transfer laws it is very similar to a proportional or linear relationship.

Testing Solid Covers: Cover 3

FIG. 7

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

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FIGURE 10 This graph represents the correspondence between the actual connection temperature data and related thermal readings from the cover’s surface. Based on heat transfer, it is similar to a proportional or linear relationship.

Testing Solid Covers: Cover 3 FIGURES 8 & 9 These thermographic images show a heated connection at 250°C, and at 50°C with a cover applied. The hottest mea-surable area on the cover was always at the same point since the cover arrangement position was never changed.

FIG. 8 FIG. 9

Thermography Under Cover 601

FIG. 10

Test Cover 601: Tandem Cable Connection

UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

Test Set 2: Perforated Covers Using the same methodology, a second test was conducted which included non-solid covers, with fixed perforations, and flexible cable openings.

The data obtained from perforated covers was similar to that of the enclosed covers: a near linear relationship between thermal hotspots as the temperature increased on the heated connection.

A noticeable difference in the imaging data from perforated covers is that when the angle of view is aligned with the cable entry points, then the temperature imaged was close to the actual bolted connection temperature. Fairly accurate temperature assessments are feasible with perforations located correctly at the most probable or statistical location of failure. Outside the lab, the challenge is that perforations are often misaligned, preventing

FIGURES 13 & 14 Thermal image of Cover 5 at 50°C. This snap coverhas flexible brush-like openings that accommo-date conductors of various sizes. The openings provide a viewpoint into the covers, and when imaged at various angles readings are possible. The thermal readings are lower than the heated connec-tion, but clearly higher than those obtained from solid covers.

FIGURE 11 Perforated cover

FIGURE 12 Corresponding thermal image of the heated connection point at 150°C.

Testing Perforated Covers: Cover 5

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FIG. 11 FIG. 12

FIG. 13 FIG. 14

UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

a direct read of the problem connection. Imaging from different vantagepoints can also be limited in a number of field applications with elevated equipment. Not maintaining safe limits of approach is simply not an option.

Test Set 3: Non-Controlled Environment The previous experiments were then replicated in an outdoor, non-controlled environment.

SUMMARYThe idea of reliable thermographic imagery of covered connections is conceptually valid, and practicably feasible.

The initial results derived from these controlled tests found that a heated connection will produce thermal patterning on any given cover. As the actual temperature of the underlying bolted connection rises, the infrared readings of the cover’s surface show a proportional or linear relationship. With some variation, this was observed for all of the tested material, at all temperatures.

It is theorized that thermal patterning derived from a cover’s surface heat would direct the maintenance operator’s attention to potential issues, and help guide further inspection and actionable information.

In practical use, the impact of fluctuating environmental conditions on the thermographic data of surface temperatures needs to be assessed when imaging. These include wind, solar, and ambient atmosphere. Technical issues also come into play, including equipment

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FIGURE 15 This is a thermal image of a bushing connection under cover 601, heated to 50°C in an uncontrolled, outdoor environment. The image shows less contrast in the thermal readings overall, but a differential can be observed in the expected hot spot.

Cover 601 in Non-Controlled Environment

FIG. 15

UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

accuracy, operator training, and physical position of the electrical components and covers in the field.

Skilled interpretation, supported by other assessment tools and field knowledge, is crucial to deriving meaningful data from thermographic images.

When taking or analyzing IR images in the field, the thermography technician’s checklist could include the base-line thermal signature of the material components, rated load, distance and angle from the target, heat generated by surrounding electrical equipment, reflections, surface heat emissions, atmospheric temperature and other environmental conditions.

These contextual factors, possibly heating or cooling parts of the target area, have a significant impact on the threshold for reliable IR temperature values and actionable data.

However, the uncertainties of qualitative thermography are not the full story.

Thermography’s most reliable and actionable information arises from more data rich forms of thermographic imaging analysis - quantitative/trending data (change over a period of time), and comparative (side by side tests of similar materials).

Quantitative analysis records thermal values over a period of time, and this data gives electrical utility operators a baseline of expected thermal values in historical conditions. It also provides the maintenance technician with a valuable reference for thermal readings in the field.

Comparative analysis, with side by side tests of similar materials, uses comparative temperature data to corroborate thermal readings under field conditions. The emissivity of a material surface is affected by many factors. However, those factors will have a similar effect on all nearby equipment. If a single cover’s surface heat signature displayed an anomalous pattern, it would be predictive of probable issues under the cover.

Quantitative and comparative thermography using data obtained under covers can be valuable tools for preventative maintenance programs. Using these forms of analysis, along with information gathered during field test imaging, a skilled thermographer could detect and flag potential issues under covers with a reliably high degree of confidence.

With validation of this concept, electricity supply operators can develop training and field testing protocols, using quantitative and comparative methods that can provide actionable preventative maintenance data.

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UNDER THE COVERS INVESTIGATING ANIMAL MITIGATION COVERS AND INFRARED THERMOGRAPHY

The preliminary findings of the Bowen Infrared study provide a strong rational for implementation of thermal imaging of connections under covers. Successful integration of these key elements in preventative maintenance would create significant impact for electrical utility systems - improving resource utilization, safety, and continuous provision of service.

ABOUT THE AUTHORSJay Bowen, Bowen & Associates, LLC and Bowen InfraredJay Bowen is an ASNT NDT Level III -TTIR Certified Infrared Thermographer and licensed master electrician. He has provided infrared training and consulting services to many hundreds of national companies for over thirty years. Jay quite literally wrote the book on infrared training having designed cutting-edge training materials. He has also directly taught thousands of infrared camera customers to properly operate and apply techniques of thermographic or infrared camera equipment.

Will Bauer & Pamela Anthony, Moment Research CorporationThe Moment Group of companies researches and develops technology in movement computing and activated data. Moment also provides technical services to select clients regarding SRED reporting, consultation papers and technical writing. Moment’s founder Will Bauer (P.Eng.) is the company’s lead technology expert and engineering consultant. Will is the inventor of a custom gesture-based media processor, Spatio, and several applications currently driving the company’s technology. Company Research Director Pamela Anthony guides research and development and lends her experience as a journalist and writer to the company’s tool kit.

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