With increasing renewable energy penetration, rural household electrification and proliferation of electric vehicles, power quality is likely to get affected owing to greater harmonics. To this end, policymakers and decisionmakers are working towards reducing power quality issues through regulatory frameworks. There are also a large number of technological solutions that can be deployed by grid operators to mitigate power quality issues at several levels such as transmission, distribution or end-use equipment.
Power Line takes a look at new and existing technological solutions for improving power quality…
Battery energy storage systems (BESS) are one of the emerging solutions to improve power quality. The system can consist of one or more batteries to meet specific requirements. These batteries are typically made of stacked cells that convert chemical energy to electrical energy and vice versa. Battery storage solutions can be used to provide electric loads with a ride-through capability in poor power quality environments.
A BESS comprises several components such as the battery management system (BMS), power conditioning system (PCS), power transformer, high tension and low tension switchgear, and energy management system (EMS). While the BMS manages the automatic and unattended operations of the battery storage system the PCS facilitates the charging and discharging of the battery. The EMS is a computerised system, which enables real-time monitoring, control and performance optimisation of the BESS system. At present, the most commonly used battery storage solution is the electrochemical battery. However, new technologies such as flywheels, supercapacitors and superconducting magnetic energy storage systems are gaining ground.
Harmonic distortions are primarily created in the system by non-linear loads. These loads feed harmonic currents back into the wiring of the equipment, thereby causing the system to malfunction. Harmonic distortions also result in poor power factor and overcurrent surges. Harmonic filters are deployed to reduce unwanted harmonics in the system and enhance overall efficiency. There are three types of harmonic filters – passive harmonic filters, active harmonic filters and hybrid harmonic filters.
A passive harmonic filter is a combination of capacitors and inductors that are tuned to resonate at a single frequency or through a band of frequencies. These filters are used to maintain total harmonic distortion below permissible limits and require constant loading for the elimination of harmonic waves. Active harmonic filters provide controlled current injection to remove harmonic current from the source side of electrical systems, thereby correcting the poor displacement power factor. This filter can be applied to single or multiple non-linear loads and can mitigate distortions under any load conditions. The hybrid harmonic filters are a combination of active and passive filters, and enable the mitigation of harmonics for both static as well as variable loads.
Static VAR compensators (SVCs) are a set of electrical devices that provides fast-acting reactive power on high voltage electricity networks. They are used to improve system stability and the system power factor. The most commonly used SVC scheme comprises a thyristor controlled reactor (TCR), thyristor switched capacitor (TSC), self-reactor, thyristor controlled reactor-fixed capacitor (TCR-FC) and the TSC-TCR.
SVCs help enhance power quality by increasing the power transmission capability of lines and improving the transient stability of the system. They also improve the power load factor, which results in lower line losses and enhances system capability. In addition, SVCs improve reliability at the end of distribution lines by stabilising voltage, thereby increasing the utilised voltage capacity. They also help balance irregular loads and reduce the stress on rotating equipment. Lastly, SVCs decrease voltage fluctuations resulting in improved power supply.
A static synchronous compensator (STATCOM) is used to regulate devices deployed on alternating current electricity transmission networks. STATCOMs are installed to support electricity networks that have a poor power factor and often, poor voltage regulation. They are used to provide variable reactive power as per the grid’s requirement. STATCOMs, like SVCs, perform the same function, though with a different reactive speed. STATCOMs enable dynamic voltage control in transmission and distribution systems, and improve the transient stability of the system. They also damp the power oscillations in transmission systems and control voltage flicker. They are not just technically feasible, but also environmentally sustainable. They use encapsulated electronic converters thereby reducing the environmental impact. STATCOMs do not significantly alter the existing system impedance and can internally generate reactive power, making them a preferred option for improving the quality of power.
A constant voltage transformer (CVT) neutralises the spikes and electrical noises in the system and improves its reliability. CVTs provide harmonic buffering and improved reservoir capacitor hold-up for the inevitable micro breaks that occur with grid protection switching. CVTs can work under a wide range of conditions. The benefits offered by CVTs include ride-through ability, sag mitigation and voltage regulation. These are designed to provide an output voltage which is not significantly affected by input voltage variations. The transformers are engineered to operate in a condition of constant core saturation so that variations in supply voltage have little effect on the core’s magnetic flux density.
Another technological solution to improve power quality is the unified power quality conditioner (UPQC). UPQCs reduce harmonics in the supply current, thereby improving current quality for non-linear loads. UPQCs can be used for power distribution systems and are connected at the point of loads that generate harmonic currents. The main functions of a UPQC are reactive power compensation, voltage regulation, and compensation for voltage sags and swells.
Smart grids have been gaining momentum owing to the increasing variability in load caused by the influx of renewables. Smart grids play an integral role in improving power quality since it depends on the flexibility and adaptability of the grid. Smart grids enable the real-time monitoring of several parameters and help in the timely detection of faults and subsequently, their mitigation. Smart grid infrastructure can thus significantly alter the country’s power quality landscape.
The way forward
Although the country has achieved a surplus power position, with increased demand, power quality needs to be improved significantly. While technological solutions lie at the heart of this initiative, other measures too can contribute to this effort. To begin with, there is a need to increase investments in the transmission and distribution segment. In fact, power quality issues can be dealt with at the planning stage with adequate quality checks. Further, it is essential to educate consumers about the issues and initiatives that can be undertaken at the ground level. For instance, consumers should be made aware of demand-side management measures and they must be encouraged to switch to robust equipment so that power quality can be regulated at the consumers’ end as well. The power sector also requires adequate investment in research and development in order to come up with solutions that are not only technically feasible but also economically viable.
There are a large number of technological solutions that can be deployed by grid operators to address power quality issues at several levels such as transmission, distribution or end-use equipment.