Motor control centresThermal imaging can be used to evaluate the operating condition of the components within motor control centers (MCCs) by comparing their relative temperatures under load. Key components include bus bars, controllers, starters, contactors, relays, fuses, breakers, disconnects, feeders and transformers.
A typical MCC is a standalone arrangement with one or more combination motor control units for controlling an AC motor in a specific application. Each unit has an external disconnect, branch-circuit and motor over-current protection and a magnetic motor starter along with pilot devices As with most electrical connections, we scan MCC components for hot spots indicating overly loose or tight connections, corrosion, overloading, unbalance, harmonics, or other problems. Our Thermal imagers can indicate the operating condition of the components within MCCs by comparing their relative temperatures under load.
What we check
We use our thermal imager to scan all components and connections within MCCs with the enclosures open and the equipment running. We measure the load at the time of each scan so that we can properly evaluate our measurements against normal operating conditions. To comply with our health and safety policy only authorized and qualified personnel using the appropriate personal protective equipment should open electrical panel covers. When a panel is open and energized, because of the possibility of arc-flash, all unprotected personnel should be kept behind a calculated and clearly delineated arc-flash boundary.
To keep the task manageable, we begin by scanning only MCCs associated with critical assets—those whose failure would threaten people, property or product. Our thermal imagers include IR-Fusion®, a technology that fuses a visual, or visible light, image with an infrared image for better identification, analysis and image management.
What we look for
In general, we look for components that are hotter or cooler than similar components under similar loads. Doing this may identify broken or undersized cables, defective insulation, faulty (corroded, too loose or over tightened) connections and electrical unbalance among phases. Connection related hot spots usually (but not always) appear warmest at the spot of high resistance, cooling with distance from that spot. Unbalance, whether normal or out of specification, will appear equally warm throughout the phase or part of the circuit that is overloaded. Harmonic unbalance creates a similar pattern. (Note: a cooler-than-normal circuit or leg might signal a failed component.) All electrical currents produce some heat. Heat alone, then, is not an indicator of problems. Equally warm conductors in all three phases represent a “good” pattern. Differentiation between phases should be investigated. A sound practice is for us to create regular inspection routes that includes all key electrical panels, including MCCs. We save a thermal images and associated temperature data of each one on our computer and track our measurements over time. This way, we will have a baseline for comparisons in order to determine whether a hot spot is unusual or not, and to help you verify a repair’s success.
What represents a “red alert?”
Equipment conditions that pose a safety risk should receive the highest repair priority. Also, guidelines say that when the difference in temperature (T) between similar components under similar loading exceeds 15 °C (27 °F) immediate repairs should be undertaken. The same organization recommends the same action when the T for a component and ambient air exceeds 40 °C (72 °F). Another approach is to treat the imminent failure of any piece of critical equipment as a red alert. The same key operations, maintenance and safety personnel who determine which production assets are critical should play important roles in quantifying “warning” and “alarm” levels for those assets.
What’s the potential cost of failure?
Since MCCs vary so much in complexity, it’s difficult to put firm figures on costs for repairs and replacements. However, one source says that the average MCC repair is between £8,000 and £50,000 with replacements costing £60,000 to £80,000.
When we discover a problem using a thermal imager, we use our specialist software to document our findings in a report that includes both a digital photograph and a corresponding thermal image of the equipment. This is the best way to communicate the problems we find and any suggestions for correcting them. Following corrective action, a new thermal image can be used to assess a repair’s effectiveness and evaluate the materials and techniques used. With this information, you can continuously improve your maintenance program for MCCs.