Harmonic Distortion can cause electrical equipment to overheat and malfunction, power factor correction capacitors to degenerate or fail, and circuit-breakers and relays to operate erratically.    To complicate matters, harmonics generated in one facility can enter a neighbouring facility through the electricity distribution system, thus making the source difficult to detect. Selectricity can assist you in detecting the presence of suspected harmonic distortion, and help identify the likely cause and solution.

What is Harmonic Distortion?

Australian electricity supply operates at a standard of 50 Hertz, or in other words, 50 cycles per second.    This means that most electrical devices are designed to operate with an alternating current, where the electrical voltage changes smoothly from positive to negative polarity and back again 50 times per second.  This smooth cycle is illustrated by the sine wave below:

For many years, electricity was predominantly used to power motors, lights and heating devices.  These early technologies are “linear loads”, meaning that the current (amperage) rises and falls in proportion to the voltage wave.  As such, they have little effect on the 50-Hertz base sine waveform.
However, in recent years many new technologies that distort the waveform have emerged. Because their current flow is not directly proportional to the voltage, these new technologies are called “non-linear” loads.  

“Non-linear” loads include Variable Speed Drives, Un-interuptable Power Supplies, PLC’s, Computers, Printers, Reduced Voltage Motor Controllers, Solid State Rectifiers, Induction Heating Equipment, Fluorescent, HID, Sodium and Mercury Vapour Lighting, Arc Furnaces, Welding equipment, AC/DC Converters and Electronic Ballasts.

Non-linear loads cause waveforms that are multiples of the normal 50-Hertz sine wave. For example, the second harmonic is a 100-Hertz waveform (2 times 50 Hertz), the third harmonic is a 150-Hertz waveform, and so on.  These multiples are called harmonics and are superimposed on the base sine waveform.  To illustrate, much like unseen undercurrents affecting the surface of literal water waves, the combination of harmonics with the base sine waveform creates a new waveform of entirely different shape.  An example of the base sine waveform, the third harmonic and the resultant distorted waveform is provided below:

As most electrical equipment expects to see a smooth incoming 50 Hertz frequency, any distortion to the pure sine wave can cause problems.  However, even if Harmonics are present, you may be unaware of any negative impact.  This is because the degree of impact is largely influenced by the levels and timing of the Harmonic Distortion, and the sensitivity of other plant and equipment.  Regardless of what the cause is, who owns it, or when it occurs, one certainty is that as Harmonic levels increase, the likelihood of experiencing problems also increases. Harmonic Distortion often causes the following symptoms:

Malfunctioning of microprocessor-based equipment
Overheating in neutral conductors, transformers, or induction motors
Deterioration or failure of power factor correction capacitors
Erratic operation of breakers and relays
Pronounced magnetic fields near transformers and switchgear

To further complicate this issue, Harmonics can sometimes be transmitted from one facility back through the electricity network to neighbouring businesses, especially if they share a common transformer. This means Harmonics generated in your facility can stress utility equipment or cause problems in your neighbour’s facility, and vice versa.

Electricity distributors have now recognised this fact and have adopted standards which define allowable Harmonic Distortion limits at incoming electricity supply points. Such standards are designed to protect both the electricity distributor and their customers.

Most facilities probably have some level of Harmonic distortion.  So the mere presence of Harmonics does not always warrant immediate and costly action.   However, if left undetected and unchecked, Harmonic Distortion poses a significant and ongoing threat to work safety, electrical equipment, plant efficiency and business profitability.
There are a number of ways to deal with Harmonic Distortion, but no one solution or strategy is the panacea for all Harmonic issues.   Just as the root causes of Harmonics are as individual as you or your neighbour’s plant, so too is the cure equally unique. 

The first step in solving Harmonic Distortion is to carefully examine your power system and electrical loads to determine the problem’s nature, source and manifestation.  In some cases highly suspect loads can be easily identified up-front, without the need to install sophisticated recording equipment.  However, often a series of Harmonic recordings is required to first detect and confirm the presence of Harmonics, establish their cause, and then lead to a solution.

The ideal time to consider Harmonics is well before their impact is felt, and particularly during the design of new facilities, or when purchasing new equipment. Known suspect loads can then be identified and appropriate preventative measures taken.

Some variable speed drive manufacturers now offer Harmonics correcting components as standard features of their drives. Others offer them as factory installed options.   Be sure to ask your drive representative about Harmonics correction when specifying new variable speed drives.

As Harmonics presents significant risk to capacitors, an independent Harmonic recording is essential before any Power Factor Correction equipment is designed or installed.  Whilst most Power Factor Correction equipment comes with blocking reactors, high levels of distortion will require more sophisticated protection.

Harmonic distortion is a unique energy issue, best left in the hands of a Supply Quality specialist.  Whatever the Harmonic issue, wherever it is caused, however it may impact, Selectricity looks forward to helping you manage this challenging energy issue.   

 

Harmonic Distortion Analysis