How to Use a Thermal Imager to Inspect Electrical Equipment
Most electrical problems within industrial facilities are manifested or are accompanied by temperature changes as an effect prior to failure.
For this reason IR thermography has become an integral part of most predictive / preventative maintenance programs. Infrared cameras can pick up small changes in temperature not visible to the human eye. It is a non contact, non destructive, and fairly simple method of detecting impending electrical problems.
It is widely known that as temperature in a conductor rises, so does it’s resistance. Conversely, as resistance increases (in most conductors) temperature rises. The majority of thermal electrical problems involve improper torque specifications or improper installation at the junction points. A loosely torqued connector effectively reduces the surface area in which current can flow and consequently an increase in the contact resistance. Oxidation build up at the connection point can also cause a rise in resistance. The origin of most conductor, insulation, and component problems can be traced to a poor connection using an infra-red camera.
Procedures for electrical predictive maintenance
Caution: Unless you are a qualified electrician DO NOT ever handle electrical wires, panels, or components.
If properly conducted infrared electrical surveys are safe, fast, and reliable. Infrared cameras are non-contact so inspections can be performed at any time without shutting down the facility.
Safety Tip: A qualified electrical contractor or facility engineer should always accompany you on the inspection. Have them open the panels and guide your access to components. They can also provide useful information on components you are inspecting (making your job easier).
Step 1: Meet with appropriate staff on site and review the service order covering what will be inspected, who will accompany the thermographer, and what type of reporting is expected (i.e. videotape, written report, and / or verbal reporting).
Step 2: Prepare inspection with the designated staff member or electrical contractor. Have them remove panels or prepare your access to components. Discuss what each type of component is to determine how you will inspect it. Have them determine (with clamp on ammeter) that electrical circuits are operating at 50% of rated load or more, if possible.
Step 3: Inspect with infrared camera. Record the sharpest images you can. Be wary of reflections and emissivity values. Keep detailed records of load reading, temperature measurements, and all infrared images of any suspect components found.
Safety Tip: When inspecting electrical panels and components be aware of your distance. High energy electrical power can arc out and ruin your day!
Step 4: Prepare the report. Write a clear concise report of all problem areas found. Include your load readings, live and thermal images, and properly written recommendations.
Hint: Whenever possible, inspect electrical systems when loading exceeds 50%
|Problem Classification||Phase to Phase Temperature Rise||Comments|
|Minor||1º – 10º C||Repair in regular maintenance schedule; little probability of physical damage.|
|Intermediate||10º – 30º C||Repair in the near future (2-4 weeks). Watch load and change accordingly. Inspect for physical damage. There is probability of damage in the component, but not in the surrounding components.|
|Serious||30º – 70º C||Repair in immediate future (1-2 days). Replace component and inspect the surrounding components for probable damage.|
|Critical||above 70º C||Repair immediately (overtime). Replace component, inspect surrounding components. Repair while IR camera is still available to inspect after.|
Compensating for wind when making temperature measurements
Wind will affect your temperature readings due to convection cooling. This can be compensated in outdoor electrical predictive maintenance applications by multiplying your temp. reading by the correction factors listed below.
|Wind Speed (MPH)||Correction Factor|