Detecting Electrical Unbalance and Overloads with Thermography

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. 

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. A severe unbalance can blow a fuse, reducing operations down to a single phase. Meanwhile, the unbalanced current will return on the neutral, causing the utility to fine the facility for peak power usage. 

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 steady state conditions with at least 40 % of the typical load. That way, measurements can be properly  evaluated and compared to normal operating conditions. 

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. However, an unbalanced load, an overload, a bad connection, and a harmonic imbalance can all create a similar pattern. Measuring the electrical load is required to diagnose the problem. 

Testo Offering: 

Testo Thermal Imager 875i offers you an entry into professional thermography. It quickly and reliably quickly and reliably detects anomalies and weak spot in materials and components. Thanks to an imaging process, energy losses and cold bridges as well as damage or overheating in industrial systems are detected without contact. Whereas with other methods, cable or pipeline systems must be exposed over a large area, with testo thermal imager 875i, a single glance is enough.

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