Drives & Controls January 2024

35 January 2024 VARIABLE-SPEED DRIVES n Tackling the hidden scourge of harmonics Harmonics in power systems can cause a range of issues. They can lead to overheating of electrical equipment, resulting in damage and shortened lifespans. They can also disrupt communication systems and reduce the e ciency of electrical equipment. AC power from the grid propels a wide array of industrial equipment such as motors, fans and pumps. To precisely control their speed, we rely on VSDs to modulate power eectively but, in doing so, generate additional harmonic frequencies. Harmonics occur when additional frequency components, multiples of the fundamental frequency – 50Hz or 60Hz, depending on the region – distort a sinusoidal signal. Harmonics introduce extra frequencies in addition to the original waveform and, along with their multiples, can be seen as being “undesirable frequencies”. The most obvious symptom is increased power consumption, and therefore higher energy bills. The harmonic frequencies draw more power without providing useful work. Beyond short-term energy use, prolonged exposure to harmonics can result in damage from overheating and can ultimately lead to poor power quality across complete systems, potentially causing damage to electronic components and shortening their lifespans. When discussing temperature increases, it’s crucial to note that eddy currents and the skin eect can play a pivotal role. Eddy currents, a side-eect of harmonics, also contribute to increased losses in the core of the equipment, especially at higher frequencies. They can also lead to the skin eect – a phenomenon that causes the alternating current to concentrate on the outer surface of the conductor, typically a wire or component made of copper. The skin eect leads to resistive (IŒR) losses, due to the conductor’s inherent resistance to the ’ow of electric current – and, consequently, to heating. Armed with this understanding, we can focus on how to mitigate and optimise installations to ensure the reliability and e ciency of electrical infrastructure. Reducing harmonics Mitigating harmonics typically involves the use of harmonic ”lters. These are electronic components designed to attenuate speci”c frequencies generated by non-linear loads – devices that draw ’uctuating, non-sinusoidal currents from the power source, causing harmonic distortion and potential issues in electrical systems. By selectively attenuating these unwanted harmonics, ”lters help maintain a cleaner and more stable power supply in the electrical system. This minimises disruptions and potential damage caused by harmonic distortions. Let’s look at how mitigating harmonics would be applied in an industrial automation system. In one project, Technidrive supported its partners in designing and implementing an automation system that combined mechanical and electrical performance optimally. The system included a premium e ciency motor (a WEG W22) controlled by a VSD. The project comprised the motor and gearbox, the electrical control panel design and build, PLC and HMI programming and commissioning, and the setup and programming of the inverter. Within this setup, harmonic ”lters were used alongside an AC drive to reduce undesirable harmonics in the network. The ”lters act like barriers, allowing desired frequencies to pass while blocking or reducing unwanted harmonics. By incorporating ”lters, the inverter ensures that the electrical system receives a cleaner power supply, minimising disruptions and potential power instabilities or damage caused by harmonic distortions. This contributes to a more e cient and reliable operation of the electrical infrastructure. Harmonics may often lurk in the background of our electrical systems, and exert a signi”cant in’uence on their operation. However, by understanding and addressing harmonics, we can maintain the integrity of electrical systems. We can eectively manage and mitigate the disruptive potential of harmonics, ensuring the reliability and e ciency of our electrical infrastructure. n Harmonics produced by VSDs can play havoc with installations. David Strain, technical director at the systems integrator Technidrive, explains why it is crucial to manage the level of harmonics in power systems and how harmonic lters can play a critical role. Variable-speed drives generate harmonic frequencies that can damage equipment and shorten their lifespans