FEATURE Drives, Controls & Motors
Innovative drives technology eliminates harmonics at source
Power-line harmonics can cause unreliable and inefficient operation of automation systems as well as a poor power factor that brings down energy efficiency. Arnold Taddeo, Global Head of Product Management for Drive Products at ABB Motion, explains how ultra-low harmonic (ULH) drives can eliminate harmonics at source
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utomation systems rely increasingly on variable speed drives (VSDs) for the energy- effi cient operation of motors,
pumps and fans. They save energy by matching the electric motor speed to the exact needs of the application. However, VSDs can introduce power-line harmonics that impact both reliability and energy effi ciency.
Harmonics might cause damage to sensitive electronic equipment, interference in communication equipment, and false readings on measurement devices. They can also trip circuit breakers, blow fuses and damage capacitors, and overheat transformers, cables, motors, generators and capacitors, wasting energy and shortening their life.
Non-linear loads effects Ideally, the alternating current (AC) power supply serving automation systems takes a pure sinusoidal waveform – see Figure 1. In reality, the use of non-linear loads creates harmonics that cause the sine wave to deviate; see Figure 2.
In addition to VSDs, harmonics
can result from equipment such as electronically-commutated motors, LED or fl uorescent lighting, mobile phone chargers, computers, uninterruptible power supplies, Wi-Fi routers, and more. A measure for the impact of harmonics is total harmonic distortion on current, or THDi. The higher this value, then the more energy is lost in the power network. As an example, a 40% THDi results in 16% greater losses than a network with no harmonics. As well as increased energy costs, the electrical system needs to be sized to carry the excess current. While a single 4kW drive, even with 100% THDi, is unlikely to cause issues, multiple drives will have a cumulative eff ect.
Addressing harmonics The overheating caused by harmonic losses can be tackled by oversizing
40 March 2022 | Automation
Figures 1 and 2: The ideal electrical supply has a perfectly sinusoidal waveform and, in practice, the waveform is often distorted by harmonics
transformers, generators and cables. This is usually expensive and often ineff ective. A better approach is to use equipment that doesn’t cause harmonics in the fi rst place, such as the newly-developed ULH drives.
ULH drives have harmonics mitigation built in, including an active front end and integrated low-harmonic line fi lter. There is no need for external fi lters, multi-pulse arrangements or special transformers. This simple installation off ers signifi cant savings in space, time and money. Compared to a conventional drive, the harmonic content is reduced by up to 95%, resulting in a typical THDi of 3%. Furthermore, as the risk of overheating is reduced, there is no need to oversize equipment.
The importance of power factor Harmonics also aff ect the power factor (PF), which describes how eff ectively the system uses its power. Ideally, a network will have a PF of unity. In some cases, utilities impose penalty charges on customers with a poor power factor. Because ULH drives mitigate harmonics, they have a positive eff ect on the power factor. A standard drive might have a true PF of around 0.78, causing it to draw an increased line current, 128% of the nominal. In contrast, a ULH drive will draw only the nominal current (100%). Essentially, ULH drives can optimise the energy effi ciency of the electrical system. The result are reduced electricity bills.
Promoting “right-sizing” Deploying ULH drives reduces the need to oversize key electrical assets. Instead, they can be optimised to match the actual load more closely. This “right-sizing” eff ect ripples through the investment costs of the entire system. For example, compared with standard VSDs, cables might be reduced in size by about 10%. Furthermore, the size of distribution transformers might be reduced by 20%, generators by 50% and switchgear and circuit breakers by 10-30%.
Positive return on investment Taking proactive action to address harmonics in automation systems by using ULH drives will soon deliver a positive return on investment. This comes in terms of improved reliability, longer equipment life, lower energy bills and reduced capital costs.
ABB ultra-low-harmonic drives family
CONTACT:
ABB
new.abb.com/drives/harmonics
automationmagazine.co.uk
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