Riding the wave: Harmonics in industry

ABB introduces its expanded range of Ultra Low Harmonic Drives, and how they are a solution to distortion in electrical networks. Manufacturers’ Monthly explains.

Harmonics in the electrical network are increasingly common, yet largely unseen. Fundamentally defined as waveforms at frequencies that deviate from the pure sinusoidal AC 50 Hz waveform, harmonics can be understood as pollution in the electrical network, as Christopher Probst, product manager, drive products at ABB Australia, described.

“If you consider harmonics as pollution in the electrical network, then the problem is that they can make connected equipment behave erratically” said Probst.

Despite being a widespread phenomenon of electrical networks, until recently, harmonics have been largely ignored.

“If you bring up the topic of harmonics, the average person may think you’re talking about
a musical instrument, however, power line harmonics appear due to electrical devices which draw current in a non-linear way.”

Harmonics are typically measured as a percentage value, called total harmonic distortion (THD). As the amount of harmonics increases, the THD percentage increases as well.

Power Line Harmonics are not high frequency (MHz, GHz), audible, radiated great distances through the air, instead harmonics are conducted.

Common devices which draw non- linear current include computers, photocopiers, and energy-efficient lighting systems.

For manufacturers, some significant contributors are motor starters, variable speed drives (VSDs) and Electronically Commutated Motor (ECM) powered fans. In fact, almost all electrical equipment is a “non-linear” load.

While VSDs provide energy savings, as well as better control performance of motors, the advantages of using a VSD far outweigh the negative effects of harmonics, but it is important to be aware of the potential problems they cause, and mitigation solutions that are available.

“Harmonics can cause things like interruptions, interference, and downtime,” said Probst. “Electrical components like cables, transformers, and circuit breakers can overheat, nuisance tripping can occur and measurement devices can give false readings. Sensitive electronics that require a pure sinusoidal AC waveform become unstable. The more non linear power there is, the bigger the harmonic currents”

The consequences of excessive harmonics can lead to overheating of cables, premature equipment failure, shortened life span and increased life cycle cost.

“It becomes more important in data centres or hospitals where a reliable electrical network is required for stable operation of sensitive electronics. Electrical supply equipment such as transformers and backup generators need to be oversized due to effects of harmonics.

“Oversizing results in underutilising capacity, and increased costs,” said Probst.

However, accounting for harmonics has its own costs involved, as Probst highlights.

“When you’re designing an electrical system, you need to take into account harmonic distortion,” said Probst. “One way to deal with harmonics is to simply oversize portions of the electrical infrastructure. Transformers and wire size may be upsized to handle the added harmonic content and heat. Backup generators also need to be oversized in systems with significant harmonic loading.”

For manufacturers, disturbances in electrical power quality lead to higher power prices, and with energy an increasingly significant cost factor, harmonics can be a contributor.

“Harmonic distortion is wasted energy, and because you’re wasting energy, you’re not using your electrical supply efficiently, and there’s a cost on the electricity bill that you pay. Harmonic currents increase the total line current,” said Probst.

In some cases, Probst has found harmonics contributing to motors running at 10oC higher, leading to the motor’s lifetime being reduced by half. As devices run hotter, they run less efficiently and are prone to premature failure.

While harmonics may not always be front of mind, a number of measures to reduce harmonics are often used, with varying effectiveness.

Addressing harmonics during the design phase allows for other parts of the electrical infrastructure to cost less. Once harmonics are addressed, further long-term cost savings are achieved through higher efficiencies and longer-lasting equipment.

“There are different methods of adding external electrical equipment to mitigate the effects of harmonics. Some can reduce harmonic distortion levels at a point of common coupling, however it makes a lot more sense to actually mitigate and control harmonics at the source of the device that’s producing them,” said Probst.

“Instead of trying to tackle harmonics by often ineffective methods, like adding filter equipment, cooling or over- dimensioning equipment, why not employ equipment that does not cause harmonics in the first place?” The prevention, rather than cure, solution that Probst referred to is ABB’s range of Ultra Low Harmonic (ULH) Drives.

“They have the harmonic mitigation technology built into the drive, and typically reduce the harmonic content to about three per cent. This is because Ultra- low harmonic (ULH) drives have an active input bridge that causes very little harmonic distortion,” said Probst.

Limits for harmonic currents are given in several national and international standards. Additionally, many transmission and distribution system operators have issued requirements especially for high power equipment connected directly to medium or high power grids. Certain industries have even set factory-specific regulations.

In addition to ULH drives mitigating harmonic distortion, power factor is also significantly improved, noted Probst.

“When external harmonic mitigation technology is added, such as a passive or active harmonic filter, power factor decreases as load decreases. That’s an undesirable outcome. Whereas a ULH drive keeps the power factor at unity, and also you get full motor control, even in low network voltage conditions the motor still receives full voltage from the ULH drive as well,” said Probst.

ULH drives have been designed to be neutral from the network point of view. The drive also provides unity power factor. This high power factor indicates that electrical energy is used efficiently, and helps to avoid possible penalty charges from the power utility provider. In addition, this also eliminates the need for compensation capacitors or active filters.

Adding a VSD to a motor will improve the true power factor. VSDs that generate less harmonics will improve the true power factor better than a VFD with a higher harmonic footprint.

Up until recently, ABB’s ultra-low harmonic drives have predominantly been used in heavy industry. Now, however, energy saving requirements and grid capacity are becoming increasingly important issues for the efficient reliable operation of plants and factories.

For these applications, ABB has expanded its range of ultra-low harmonic drives.

ABB’s existing range of ACS880 Industrial ULH Drives cover power ranges from 4 kW to 3.2 MW, for all industries and applications such as mining and metals, oil and gas, power, pulp and paper, marine, food and beverage.

Released now are drives designed for the specific needs of the heating ventilation and air-conditioning industry (HVAC) and the water industry. The ACQ580 Water Drive and ACH580 HVAC drive are now also available with ULH technology.

“The reason that ABB has focussed on industrial, water, and also HVAC, is that these particular applications are not only susceptible to harmonics,” said Probst. “But also, because of the number of drives used for motor controls on these particular applications, the harmonic content from these sites can be quite large, assets and equipment can be quite expensive to maintain or replace.

“ULH drives provide a lot of advantage in this space, because not only do they lower harmonic content contribution at the source to about three per cent, they also provide unity power factor, extend the lifetime of the assets, and fulfil requirements set by harmonic standards as well.”