Power quality problems are one of the major causes of unscheduled downtime, equipment malfunction, and damage. Reliability and consistency of electricity supply are critical to businesses, from industrial plants, medical facilities, data centers to office buildings.
Today, electrical installations are exposed to a great deal of power quality problems; 80 percent of these disturbances are typically generated by installed equipment. In industrial facilities, for example, such disturbances can be caused by non-linear loads like arc welders or variable speed drives, capacitor switching, or large motor starts. In commercial buildings, electronic equipment like computers, UPS, and servers may also generate additional power quality disturbances.
The other 20 percent of power quality disturbances come from the energy provider: even the most advanced transmission and distribution systems are not able to guarantee 100 percent energy availability. Even with 99.99 percent energy availability, the equivalent interruption time amounts to 52 minutes every year.
Impact of Harmonics
Each facility has its own specific power quality issues, depending on the installed loads, equipment, and the quality of supplied energy. One such power quality issue is harmonics.
Any electronically controlled single-phase load, such as LED lighting, generates neutral harmonic current. This excess current results in excess energy, or wasted energy, that must be supplied by the utility, meaning you pay the utility to supply more power than your system actually requires. For installations that rely heavily on this type of load, the entire installation must be overdesigned, demanding a higher initial investment, to account for that excess energy loss. All the excess energy on the system also wreaks havoc on your equipment, and can ultimately lead to downtime and loss of productivity.
Harmonics is the generalised term used to describe the distortion of a sinusoidal waveform by waveforms of different frequencies. Harmonics are usually defined by two main characteristics – amplitude i.e. the value of the harmonic voltage or current and the order i.e. the value of their frequency with respect to the fundamental frequency – the presence of varying amounts of harmonics on a network is called distortion. Harmonics are generally produced by non-linear loads which behave as current sources that inject harmonics into the network.
Harmonics lead to unwanted tripping of protection devices, induced interference from LV current systems (remote control, telecommunications), abnormal vibrations and noise, damages due to capacitor thermal overload and faulty operation of non-linear loads.
Solutions for Harmonics Mitigation
Each power quality problem requires specific corrective equipment. The equipment recommended for harmonic mitigation is the active filter due to its flexibility and high correction performance. In many modern facilities, since the equipment mix is constantly changing, it results in a drifting of the harmonic spectrum. Active filters are often useful in these circumstances. They are shunt devices in which the harmonic content is measured on one cycle and an exact replica is produced from within the conditioner and fed onto the supply on the next cycle.
Specifically, Schneider Electric’s AccuSine PCSn series power quality solutions are flexible, high performance active harmonic filtering solutions to stabilize electrical networks by providing harmonic mitigation and power factor correction, and load balancing.
AccuSine PCSn is the new solution specifically designed for commercial buildings, light industry, and other less-harsh environments. AccuSine PCS+ is specifically designed for harsh electrical conditions, for heavy industrial applications including mission critical environments. Further, the AccuSine PFV+ is an electronic VAR compensation (EVC) employing a multi-level IGBT technology with advanced control systems platform to perform leading or lagging power factor correction (PFC) and flicker mitigation. It is the ideal solution for PFC applications subject to high voltage distortion or subject to dynamic fast changing loads.
In addition to 3-phase mitigation, AccuSine PCSn has the ability to compensate for neutral harmonic currents, typically present in building and commercial environments where single-phase non-linear loads are present. Although typical industry standards call for THDi < 5%, AccuSine PCSn best-in-class performance reduces THDi to less than 3 per cent. Another advantage is the multi-mode functionality which enables addressing system needs through multiple compensation modes – active harmonic mitigation, power factor correction and mains load balancing. Also, AccuSine PCSn can be connected to the EcoStruxure Power software platforms to gain remote system level visibility. Further, the AccuSine PCSn is an adaptable and scalable solution. More AccuSine+ modules can be added as your harmonic mitigation needs change, easily integrating new modules through intelligent paralleling capabilities. Further, proprietary AccuSine+ paralleling algorithm can save time by enabling intelligent functionality such as automatic CT sizing and polarity, detection and correction, Insusceptible phase rotation and automatic parallel ID assignment.
Conclusion
In sum, when power quality is imperfect due to disturbances such as interruptions, voltage dips or harmonic pollution, business suffers. It is an area of growing concern for end users due to the frequency of occurrence and financial impact of issues: 30 – 40 percent of all unscheduled downtime today is related to power quality problems. In the industry sector, for example, the cost of poor power quality can reach four percent of annual turnover and is often equivalent to the total balance payable on a facility’s energy bill. Thus, capital investment in harmonic filtering equipment such as the AccuSine solution can result in a healthy return of investment.