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Application Notes:
Detecting Electrical Unbalance and Overloads |
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Thermal images are an easy way to identify apparent temperature differences in industrial three-phase electrical circuits, compared to their normal operating conditions. By inspecting the thermal gradients of all three phases side-by-side, technicians can quickly spot performance anomalies on individual legs due to unbalance or overloading. |
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Electrical unbalance can be caused by several different sources: a power delivery problem, low voltage on one leg, or an insulation resistance breakdown inside the motor windings. Even a small voltage unbalance can cause connections to deteriorate, reducing the amount of voltage supplied, while motors and other loads will draw excessive current, deliver lower torque (with associated mechanical stress), and fail sooner.
What to Check?Capture thermal images of all electrical panels and other high-load connection points such drives, disconnects, controls and so on. Where you discover higher temperatures, follow that circuit and examine associated branches and loads.
Check panels and other connections with the covers off. Ideally, you should check electrical devices when they are fully warmed up and at a steady state conditions with at least 40 % of the typical load.
What to Look For?Equal load should equate to equal temperatures. In an unbalanced load situation, the more heavily loaded phase(s) will appear warmer than the others, due to the heat generated by resistance.
What Represents a "Red Alert?"Repairs should be prioritized by safety first i.e., equipment conditions that pose a safety risk followed by criticality of the equipment and the extent of the temperature rise.
What's the Potential Cost of Failure?Motor failure is a common result of voltage unbalance. Total cost combines the cost of a motor, the labor required to change out a motor, the cost of product discarded due to uneven production, line operation and the revenue lost during the time a line is down.
Follow-up ActionsWhen a thermal image shows an entire conductor is warmer than other components throughout part of a circuit, the conductor could be undersized or overloaded. Check the conductor rating and the actual load to determine which is the case.
Use a multimeter with a clamp, a clamp meter or a power quality analyzer to check current balance and loading on each phase.
Click here to download the full pdf: Detecting electrical unbalance and overloads » | |
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