Signal conditioning T
raditionally, harmonics in the UK were regulated through the EN50160 power quality standard and the Engineering Recommendation G5/4. They were previously regarded as falling between the 50 Hz to
2.5 kHz range, or between the 1st and 50th order. However, G5/5 has taken the limit up to 5 kHZ, or the 100th harmonic. What does this mean? Most power quality engineers are using measuring devices incapable of seeing above the 50th order. While EN50160 is a good benchmark, it was never designed to focus on the end user’s own asset protection. It was designed to ensure the end user does not impact the power network and impact others at the common point of coupling (PCC). Harmonic limits should be thought of as speed limits, with sites keeping under them to reduce risk.
A HIDDEN COST IN MITIGATION Every sector is impacted, including the UK’s water industry and its various sites that use high-power drives and motors. Often, active front end drives are provided as the solution to keep the harmonics down. While they do a good job at that, the extra two to three per cent in losses compared to a standard variable speed drive (VSD) requires more climate control in the control room. This potentially equates to 6 kW’s of additional heating on a typical Duty, Assist, Standby on a 90 kW application.
Operators also need to consider solving the harmonic issue locally at source or at the common point. Many factors should be considered as there is no one-size-fits-all solution. The nature of the loads and how dynamic they are will also play a role, along with budget and space constraints.
ENSURING POWER QUALITY ACROSS THE SPECTRUM
Power quality is a pressing issue in industrial environments and even the slightest harmonic currents or utility-level distortion can inflict costly damage on electrical equipment. The new Engineering Recommendation G5/5 has extended the values for planning and compatibility levels to the 100th order (5 kHz), broadening the reach of emissions testing. Here John Mitchell, global sales and marketing director of power quality specialist CP Automation, discusses the harmonics gap and how operators can overcome it.
The recent change in regulation means operators and end users should assess the likelihood of harmonic distortion and other noise impacting their equipment. It could also offer answers to unsolved power quality issues.
UNCOVERING THE GAP
Harmonics and electromagnetic interference (EMI) are disruptive, triggering equipment failures across the frequency spectrum. Fire alarms can go off at random, components can overheat, and power supply units (PSU) often fail.
One area that is now being addressed in Europe and partly by G5/5 is the area between harmonics and EMC, called supra- harmonics. These are graded in two areas of noise, 2-9 kHz and 9-150 kHz. This is an area most power quality devices cannot read, and sites can be mistakenly given a clean bill of health by power quality engineers. Often, they unknowingly cannot measure this noise because the equipment they are using only works to the old standards of 2.5 kHz (50th order). That is
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March 2023 Instrumentation Monthly
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