Harmonics have been around longer than you might realize. Since the development of the very first AC generator more than a century ago, electrical systems have suffered the plague of harmonics.
Harmonics are voltages and currents, that contain frequencies at integer multiples of the fundamental power frequency (usually 60Hz for American power). Because they detract from the pure sinusoidal voltage — which is desirable in efficient electrical systems — these harmonics, if large enough, can cause power quality problems, and potentially lead to equipment malfunction or system failure.
Harmonic distortion in electrical systems has become a growing problem for facility managers, engineers, and various professionals who work with large electric motors. Though the presence of harmonics doesn’t make it impossible for factories to operate, they do increase the chances of lost productivity and high maintenance expenses.
So, what can you do to reduce harmonic distortion in electrical systems?
Get a Power Quality Site Survey
While it’s possible to manage and reduce harmonics in electrical systems, the first step (as with any problem) is accurately identifying the problem. The issues caused by harmonic distortion are frequently misdiagnosed — oftentimes leading responsible personnel to take actions that fail to address the true underlying cause.
When trying to correct issues in your electrical system, the best place to start is to schedule a power quality site survey conducted by a trained professional. An expert in electrical maintenance and repair can give you a comprehensive idea of your power supply; and hone in on the true cause of your system’s inefficiency.
Often, this process involves the use of monitoring software — which allows you to see firsthand whether harmonics exist in your system, and how severe the problem is. On top of that, the monitoring software used in a site survey can identify other existing problems in your system; such as inadequate wiring, interruptions in power flow, voltage issues, and more.
Once you have clearly identified that harmonics are indeed the source of your problem, you can begin to address the issue.
Try a Filter or Low Harmonic Drive
Most AC drive systems use diode rectifiers — which can lead to high levels of harmonics. To mitigate the damaging effects of distorted harmonic currents, you can install an active or passive filter to block some of those currents.
While a passive filter removes the part of the spectrum of distorted harmonics associated with VFDs, an active filter can be more effective depending on the application. Through your power quality site survey, a professional can identify which frequencies are most counterproductive to your system, and it’s possible you can use an active filter to address those particular frequencies.
Alternatively, you can opt for a low harmonic drive that has a built-in LCL filter and active front end. This is like having an inverter in front of an inverter. The active front end (inverter) generates opposing harmonics to cancel those harmonics generated by the inverter driving the motor. These drives are more expensive than a non-filtered drive with a separate harmonic filter, but they are quite effective.
The type of filtering method you choose for your system will depend on your unique issues and resources. Ask the technician during your site survey for recommendations on which method is best for your electrical system.
Install a Variable Frequency Drive
Typically, people install variable frequency drives (VFDs) into their system to reduce the total power consumption where appropriate. In this case, a VFD will also reduce the power load on the feeder transformer, and when coupled with a harmonic filter, the feeder transformer will benefit with longer life from reduced heating.
Though a VFD with a harmonic filter may not be the only solution to reducing harmonics from your electrical system, a professional engineer can give you insight into whether this update will benefit your operations. With a VFD, you’ll also get the benefit of less wasted energy — in most cases, installing a VFD is a win-win for manufacturers.
Adjust the Capacitor
When a specific harmonic frequency occurs in a system with a capacitor, a crossover point exists, where the capacitive and inductive reactances are the same. This point is the parallel resonant point, and leads to a problem known as harmonic resonance.
Harmonic resonance can result in high voltages and high harmonic currents, both of which are detrimental to the electrical system. Though adjusting the capacitor won’t prevent harmonics, it will shift the resonance frequency to remove the damage that occurs as a result of harmonic resonance.
Engineers can choose to adjust the system’s capacitor in a few ways:
- Remove the capacitor completely — though this could lead to a lower power factor, higher distribution losses, and possible lower voltage.
- Move the capacitor to a different area in the system — though this is rarely an option for industrial users.
- Change the value of the capacitor — so it’s less likely to resonate with harmonic frequencies.
Caring for Your Electrical System
The presence of harmonics will not always lead to measurable problems, but they can and often do create havoc in electrical systems. From overheating distribution transformers, to damaging electronic equipment; you should strive to reduce harmonics in your system wherever possible, if you want to achieve maximum efficiency and productivity. Contact a professional in electric motor maintenance and repair to find out what measures you can take to prevent harmonics from occurring, and address the identified current issues plaguing your system.