Industrial electrical installations are among the most complex, delivering power to a broad range of equipment that includes automatic controls, process-specific machinery, chillers, cooling towers, fans and lighting installations. Given the complexity of industrial electrical installations, troubleshooting can be quite a challenge, and pinpointing an issue can be nearly impossible without the right measurement tools. Unlike mechanical issues, which tend to give a warning in the form of excessive vibration and noise, electrical issues can stay under the radar until it is too late, causing sudden equipment failure.
Motors and other loads that rely on electromagnetism draw two types of power: real power is that which is converted to useful work, while reactive power is used to establish a magnetic field, but it oscillates back and forth between the source and the load without being consumed. The sum of real and reactive power is called apparent power, but keep in mind that they are out of phase by 90°, so their sum is vectorial and not algebraic. In turn, the ratio of real power to apparent power is called power factor. Consider the following example:
Low power factor by itself does not cause equipment failure, but your client’s power bills can increase drastically if PF is not controlled. Utility companies establish a minimum power factor for commercial and industrial clients, typically 90%, and all energy consumers that fall below are subject to extra charges. In addition, utility companies apply a formula that makes the power factor charge higher as its measured value becomes lower! Fortunately, low power factor can be corrected easily by following the procedure below:
Harmonics are more challenging to handle than low power factor. Basically, they are the result when non-linear loads cause distorted currents, and the harmonic content of an electrical installation can become very high when there is a lot of digital equipment, automatic controls or variable-speed drives.
Fortunately, power quality analyzers can measure harmonics along with power factor, which allows you to diagnose both issues with a single measurement run. Once you have a snapshot of the overall harmonic content in an installation, you can proceed to measure harmonics for specific pieces of equipment such as large VFDs and control boards, and specify the corresponding harmonic filters (example below).
Harmonics are notorious for their ability to overload and damage neutral conductors. Unlike normal currents, harmonic currents do not cancel out in a three-phase system and add up at the neutral; if an installation has severe issues with harmonics, you may find that the neutral conductor is actually carrying more current than the phase conductors.
Electrical distribution boards, protection devices and controls are prone to overheating when there are poor connections between different electrical elements, and the accumulation of dust or rust can have the same effect. Poor contact increases resistance, and as you might recall from basic electricity courses, higher resistance results in more heat dissipation.
Hot spots can be detected visually once heat has caused damage. For example, you may notice that equipment housings have been deformed by heat, or the area surrounding the hot spot could have blackened. However, these issues can be detected much earlier with a thermal imaging camera.
A three-phase voltage supply should ideally provide rated voltage at all terminals when subject to full load. However, real-life installations generally suffer from two issues, together or in combination:
When there is excessive voltage drop, there are two likely consequences:
With voltage imbalance, on the other hand, the most likely causes are the following:
If all motors are drawing balanced currents, the imbalance is most likely due to poor distribution of single phase loads. Of course, both issues may be present at once as well. To bring the three-phase voltage supply back to balance, it is necessary to redistribute single-phase loads and service any motors with damaged windings.