The rise of non-linear loads in industrial environments over the last two decades has resulted in the growing problem of harmonic currents and utility-level voltage distortion. Facing a lack of awareness, the industry has struggled to implement effective mitigation techniques. Here, global business development manager of CP Automation, John Mitchell, discusses offers useful tips for mitigating harmonics
Voltage distortion, caused by current harmonics can wreak havoc in a plant, its equipment and the mains power supply. Damage can be serious and varied with the most common symptoms including voltage notching, motor vibration, arcing on bearings, nuisance tripping, electromagnetic interference (EMI/RFI) and overheating.
The very first place to start is to ensure you comply with regulations. International harmonic control requirement, IEEE-519, limits “the maximum frequency voltage harmonic to 3% of the fundamental and the voltage total harmonic distortion (THD) to 5% for systems with a major parallel resonance at one of the injected frequencies.” Some form of filtering is subsequently recommended.
We’re lucky in the UK to have a stiff power grid, but this is not true everywhere. Developing countries often aren’t as lucky. Weak grids with an unreliable supply and inadequate infrastructure are common in other parts of the world. The power ratings on products are often based on calculations performed in ideal conditions. Buyers would be wise to note that these products may perform adversely in weak grids and may not perform to IEEE-519 standards in these conditions.
Remember to always stay on your toes. The last few decades have seen a rise in the use of non-linear loads such as transistor based variable speed drives (VSDs) and line commutated DC drive systems. The processes of high frequency switching and pulse width modulation (PWM), introduce unwanted multiples of the fundamental 50hz frequency in the form of harmonics. Knowing what options are available to you can help the overall efficiency of the harmonic mitigation process.
Passive and active harmonic solutions can be installed in both series and parallel (shunt) configurations within a system. Series solutions operate in line with the load, meaning that units must be sized for the full current load. Shunt units can be sized only for the harmonic disturbance. There is a clear decision to be made between series-passive, shunt-passive, series-active and shunt-active solutions.
