Looking for power quality problems behind closed doors
Troubleshooting or testing for power quality problems usually requires technicians to take electrical measurements at specific pieces of equipment while the equipment is energized. This puts them at risk and requires them to use appropriate personal protective equipment (PPE). However, technicians and electrical workers can find some power quality and electrical reliability issues without the associated risks—thanks to thermal imaging.
Experienced electrical workers use infrared (IR) cameras or imagers to perform thermographic inspections, which should be performed at least annually according to NFPA 70B. Historically, IR inspections required equipment to be fully energized and running and panels to be open so that switchgear or panel components were visible. However, open panel inspections expose workers and equipment to hazards such as arc flash, shock, or electrocution due to potential contact with energized electrical components.
Equipment and components
IR windows installed in panel doors eliminate the need for panel doors to be open. They allow thermographers or trained electrical workers to acquire images of energized and loaded electrical components safely because the doors are closed. Equipment and components that technicians can inspect with thermal imagers typically include:
Unbalances, overloads and intermittent connections
Although IR thermography won’t detect every power quality problem, it is very useful when performing preliminary checks for unbalances, overloads and intermittent connections. Most thermal imaging is a comparative, qualitative process. Look for spots that are unexpectedly hotter than similar equipment under the same load conditions. Hotspots could indicate unbalanced loads, triplen (third harmonic) current in neutrals, overload/excessive current, loose or corroded connections, insulation failure, component failure, wiring mistakes or underspecified components.
When looking for problems with a thermal imager, maximum electrical equipment loading conditions are ideal. If maximum loading is not possible, the equipment should be under at least 40 % of nominal load.
When checking for three-phase unbalance, capture thermal images of high-load connection points such as drives, disconnects and controls. Compare the phases, checking for apparent temperature differences. Hot conductors may be undersized or overloaded. Heavily-loaded phases will appear warmer, while a comparatively cooler circuit leg could indicate a failed component. Since an unbalanced load, overload, bad connection and harmonics can create similar thermal patterns, follow up with actual measurements using a digital multimeter (DMM), power quality analyzer, or harmonics analyzer to troubleshoot and diagnose specific problems.
When checking for connection and wiring problems, look for connections with higher temperatures than similar connections under the same electrical and loading conditions. Hotspots associated with connection problems typically appear warmer at the spot of high resistance and cooler as distance from the spot increases.
Eventually, every plant experiences electrical equipment failure and power quality problems. When equipment or components deteriorate, often thermography can detect their warning signs before they fail. Using IR windows enables experienced thermographers and electrical workers to locate problems before they become major downtime issues—safely.