Power quality is increasingly becoming an area of concern and is being widely regarded as a vital constituent of a well-developed power system. Power quality, in simple terms, refers to reliability and availability of the supply network. In India, the concept has gained significance over the past few years, especially in light of the government’s target to provide 24×7 “quality” power to all by 2022. Meanwhile, the electricity grid is becoming increasingly complex with the integration of large renewable energy capacity, increase in distributed generation, and addition of complex loads in the system, thus bringing power quality issues to the fore.
Any significant deviation in the magnitude, frequency, waveform or symmetry of line voltages is a potential power quality problem. Poor power quality not only causes performance degradation and premature failure of electrical equipment but also results in increased system losses and financial losses.The most common causes of poor power quality include low power factor, harmonic disturbances, load imbalances and voltage variations.
Some of the measures that can be taken to improve power quality are the deployment of automatic voltage control devices, active power factor correction devices, source and load balancers and digital substations; control and management of peak power; and efficient reactive power management. In addition, technology solutions such as static VAR compensators (SVCs) and static synchronous compensators (STATCOMs) at the transmission level; and unified power quality conditioners (UPQCs) and harmonic filters at the point of loads can be deployed. A one stop solution to overcome the power quality issues is Schneider Electric’s VarSet, its series of smart capacitor banks. VarSet provides power factor correction, harmonic filtering, energy loss reduction, and lessening of voltage drops on low voltage networks. It is not only suitable for new construction but also for retrofit applications in commercial buildings, industrial, and utility enterprises.
Power factor correction
All AC electrical networks consume two types of power: active power (kW) and reactive power (kVAr). The active power is the real power transmitted to loads such as motors,lamps, heaters, etc. The electrical active power is transformed intomechanical power, light or heat.The reactive power is used only to power the magnetic circuitsof machines, motors and transformers. The circulation of reactive power in the electrical network has major technical andeconomic consequences. For the same active power, a higher reactive powermeans a higher apparent power, and thus a higher current must be supplied.This leads to oversizing of transmission and distribution networks by utilities, increased voltage drops and sags along the distribution lines, and additional power losses.
If reactive energy can be generated at the load level, it can prevent the unnecessary circulation of current in the network. This is what is known as “power factor correction” (PFC). This is obtained by the connection of capacitors, which produce reactive energy in opposition to the energy absorbed by loads such as motors. The result is a reduced apparent power, and an improved power factor. The power generation and transmission networks are partially relieved, reducing power losses and making additional transmission capacity available.
PFC equipment criteria
Optimised reactive energy management/compensation offers several economic and technical advantages including savings on utility bill (by eliminating penalties on reactive energy and reducing power losses generated in the equipment), increase in service capacity, reduction in installation cost, improvement in voltage stability and reduction in harmonics.
The power factor correction equipment should be selected based on the required reactive power, the mode of compensation, type of compensation and the expected working conditions.The location of low-voltage capacitors in an installation constitutes the mode of compensation, which may be central (one location for the entire installation), group (section-by-section), or at load level. In principle, the ideal compensation is applied at a point of consumption as the reactive energy is produced exactly where it is needed, and adjusted to the demand. Meanwhile, central compensation is convenient for a stable and continuous load factor and group compensation for a large installation, with workshops having different load factors.
The compensation differs by type depending on the performance requirements and complexity of control. It could be fixed, by connection of a fixed-value capacitor bank; automatic, by connection of a different number of steps allowing adjustment of the reactive energy to the required value and dynamic, for compensation of highly fluctuating loads. Fixed compensation capacitors are installed at the terminals of inductive loads (mainly motors), at busbars supplying numerous small motors, at inductive appliances for which individual compensation would be too costly and in cases where the load factor is reasonably constant. Automatic compensation is useful where the active-power and/or reactive-power variations are relatively large, while dynamic compensation is required when fluctuating loads are present, and voltage fluctuations have to be prevented.
Further, the operating conditions have a great influence on the life expectancy of capacitors. Parameters like the ambient temperature (°C), expected over-current, maximum number of switching operations/year and required life expectancy should be taken into account while selecting the capacitor bank.The end-application of the capacitor bank, be it some industry (textiles, wood, paper, etc) or commercial consumer such as hospital, hotels, etc. or energy infrastructure (substation, turbine, etc.), also plays a crucial role in determining the nature of capacitor required.
VarSet LV, the low voltage power factor correction solution of Schneider, offers a unique combination of abilities giving superior reliability and enhanced performance across a broad range of applications. They provide overload and short circuit protection at each stage, are convenient to install, have long life and are easy to maintain. They are also easy to commission due to pre-settings and smart power factor controller Varplus Logic. It also has smart monitoring and measurement features that allow secured operations and maintenance of the capacitor bank even from a remote location. They are fully type tested in compliance with IEC/EN 61439-1 and IEC 61921, or in compliance with CSA 22.2 NO 190, UL810 & UL 508a. They are available for various network voltages including 230V-400V-415V (50Hz) and 240V-400V-480V-600V (60Hz). Further, they provide protection against direct contact, mechanical shocks as well for indoor applications (especially useful for dusty and industrial environments). They have multiple alarm functions for temperature, harmonics, voltage, overload, etc.
VarSet helps in lowering the operating and capital costs and provide quick return on investment. It has the potential to reduce capital expenses up to 30 per cent; and reactive energy billing penalties and operating expenses up to 10 per cent. It also helps improve power system and equipment reliability up to 18 per cent while reducing the CO2 emissions by up to 95kg for every kVar of power factor installed.
To sum, power factor correction helps lower operating and capital costs and improve efficiency. Compensating for reactive power and harmonic distortion with capacitor banks is one of the easiest ways to quickly maintain power factor at an ideal level for maximum power system efficiency and cost reduction.