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Application Notes:
Motor Control Centers |
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Thermal 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, branchcircuit and motor over-current protection and a magnetic motor starter along with pilot devices located on the panel door.
What to check?Use your thermal imager to scan all components and connections within MCCs with the enclosures open and the equipment running. Measure the load at the time of each scan so that you can properly evaluate your measurements against normal operating conditions. Caution: Only authorized and qualified personnel using the appropriate personal protective equipment should open electrical panel covers.
What to look for?In general, look for components that are hotter or cooler than similar components under similar loads. Doing this may identify broken or undersized wires, defective insulation, faulty (corroded, too loose or over tightened) connections and electrical unbalance among phases. Be aware that connection related hot spots usually (but not always) appear warmest at the spot of high resistance, cooling with distance from that spot. One source, reports that 25 % of all miscellaneous electrical apparatus failures are caused by loose electrical connections.
What represents a "red alert"?Equipment conditions that pose a safety risk should receive the highest repair priority. Also, guidelines provided by the NETA (InterNational Electrical Testing Association) say that when the difference in temperature (DT) 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 DT 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.
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.
Follow-up actionsWhen you discover a problem using a thermal imager, use the associated software to document your findings in a report that includes both a digital photograph and a corresponding thermal image of the equipment. That's the best way to communicate the problems...
Click here to download the entire pdf: Motor control centers » | |
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