Electrical, insulation and thermal measurements for motors and drives
Most facilities need to get maximum life out of their motors, because they are expensive to replace in terms of both money and labour. Electrical, insulation resistance and thermal measurement are three tests that can troubleshoot motors, drives, and associated electrical panels and prolong their operational lifetime. Used together, thermal imagers can detect potential problems and insulation resistance and electrical tests can determine the cause. Our handheld thermal imagers can collect heat signatures from a range of motors, from 1000 hp down to 5. A thermal imager is good for spot checks, to see if motors and associated panels and controls are operating too hot, and for troubleshooting, to track down the specific failed component at fault. It can also check for phase imbalance, bad connections, and abnormal heating on the electrical supply.
Using an insulation multimeter we can also perform most of the other tests you need to troubleshoot and maintain motors. When a motor is having problems, we first check the supply voltage and then use insulation testing to check the starter and control contacts, measure the insulation resistance of the line and load circuits to earth, and winding resistance phase to phase and phase to earth.
A motor’s heat signature will tell us a lot about its quality and condition. If a motor is overheating, the windings will rapidly deteriorate. In fact, every increase of 10°C on a motor’s windings above its design operating temperature cuts the life of its windings’ insulation by 50 percent, even if the overheating is only temporary.
If a temperature reading in the middle of a motor housing comes up abnormally high, we take a thermal image of the motor and find out more precisely where the high temperature is coming from, i.e. windings, bearings or coupling. (If a coupling is running warm it is an indicator of misalignment.)
There are three primary causes for abnormal thermal patterns; typically most are the result of a high-resistance contact surface, either a connection or a switch contact. These will usually appear warmest at the spot of high-resistance, cooling off the further away from the spot.
The left thermal image shows a classic pattern in the center phase connection on the line side of a breaker; note how the conductor cools off at the top of the image. Load imbalances, whether normal or out of specification, appear equally warm throughout the phase or part of the circuit that is undersized/overloaded. Harmonic imbalances create a similar pattern. If the entire conductor is warm, it could be undersized or overloaded; check the rating and the actual load to determine which. Failed components typically look cooler than similar, normally functioning ones. The most common example is probably a blown fuse. In a motor circuit this can result in a single phase condition and, possibly, costly damage to the motor.
Insulation problems on motors and drives are usually caused by improper installation, environmental contamination, mechanical stress or age. Insulation testing can easily be combined in with regular motor maintenance, to identify degradation before failure, and during installation procedures to verify system safety and performance. When troubleshooting, insulation resistance testing can be the missing link that enables us to get a motor back into operation the easy way, by simply replacing a cable. Insulation testers apply a dc voltage across an insulation system and measure the resulting current. This allows them to calculate and display the resistance of the insulation. Typically, the test verifies high insulation resistance between a conductor and earth or high insulation resistance between adjacent conductors.
Two common examples include testing motor windings for insulation from the motor frame and checking phase conductors for resistance from bonded conduit and enclosures. Insulation multimeters combine the insulation resistance functions above with the other tests needed to investigate motor, drive, and electrical trouble, from basic supply measurements to contact temperature. The key difference is that insulation resistance tests are performed on de-energized systems, while electrical tests (and thermal) are almost always performed on live, operating systems.