Technology Play

Advanced solutions for power quality improvement

While the country is witnessing an increase in power generation, the supply of power reaching end-consumers lags in quality. Poor power quality often results in outages and voltage fluctuations that damage equipment, thereby causing significant losses to consumers particularly in the industrial and commercial segments. It also drives the adoption of diesel generators and renewable energy sources for captive use.

Power quality is a combination of voltage and frequency profiles, harmonics and reliability of power supply. It also depends on the degree to which power supply conforms to the ideal profile of stable, uninterrupted and disturbance- free power. Power quality issues include voltage sags, a sharp short-term decline in voltage that can be caused by switching operations and faults in the transmission operations. Another problem is interruption in the supply of power often when the voltage drops below 10 per cent of the original value for not more than one minute. In addition, harmonics distortion is a significant issue that needs to be addressed to improve the quality of power in the country. It is a result of the non-linear nature of loads on the power system. The issue continues to increase with the increase in renewable power as it is dependent on an inverter-power grid interface that leads to harmonic distortion.

Power Line outlines the technologies and solutions that can be employed to enhance the quality of power supply…

Static VAR compensator

The static var compensator (SVC) is a reactive power compensation device that consists of a control system, thyristor valves, capacitor banks and reactors. SVCs can improve the quality of power by improving the power transfer capability,  reducing transmission losses and mitigating power oscillations. SVCs can improve power quality at the transmission as well as distribution level. It can help stabilise voltages in weak transmission systems, reduce losses and help increase the transmission capacity, thereby eliminating the need for new lines. SVCs also provide a higher transient stability limit while damping minor disturbances and power oscillations in the system, resulting in greater voltage control and system stability.

In addition, SVCs help stabilise the voltage at the receiving end of the distribution lines, which helps increase the utilised voltage capacity. It also helps reduce the reactive power consumption, thus decreasing the loss of power. SVCs are also responsible for balancing irregular loads and reducing the stress on rotating equipment. Moreover, these help decrease voltage fluctuations and flickers while dampening the harmonic distortion, resulting in improved power supply.

STATCOM

Electricity generation is often variable, with loads fluctuating within hours, leading to grid imbalances and voltage fluctuations or a complete voltage loss. This can be attributed to the inherent ability of electrical loads to produce and absorb power. Statistic synchronous compensators (STATCOMs) are used to provide variable reactive power as per the requirement at the grid considering the voltage fluctuation. STATCOMs are similar to SVCs in their function, with reactive speed being their differentiating factor. A STATCOM reacts according to the voltage source converter principles and unique pulse width modulation, and has the ability to switch within milliseconds.

STATCOMs do not require multiple harmonic filters. This helps in reducing the size of the system. Also, these are compatible with switched or fixed air core reactors and capacitors with voltage source converters to achieve any range of reactive power. One of the key benefits of STATCOMs is that installing these at one or more nodes on the grid increases the grid’s power transfer capability. This is because STATCOMs improve voltage stability and help maintain seamless voltage under variable conditions.

Constant voltage transformer

A constant voltage transformer (CVT) is used to protect the transmission system from spikes and electrical noise. It provides a barrier to these disturbances while also working in reverse mode to prevent any such elements from disturbing the main load at the grid. CVTs are capable of correcting main voltage sags and surges by keeping the iron core of the transformer’s secondary section saturated, thereby generating a constant voltage output. CVTs also provide protection from lightning by presenting low impedance to the grid. The key benefits of CVTs include:

  • Voltage regulation: CVTs are able to drown any considerable input voltage variations and provide nominal output voltage regulation.
  • Sag mitigation: A CVT ensures that any voltage sag is rectified immediately though it is not effective during instantaneous voltage interruptions or extremely deep voltage sags.
  • Ride-through ability: CVTs have a unique capability to store energy for about half of the cycle due to their specific design, which when combined with an inverter and a static transfer switch can provide uninterrupted power transfer to an alternate source. In case of a fault or overload, this feature of a CVT enables it to maintain power supply to the grid, thus preventing a total loss.

Harmonic filter

Within an alternate current circuit, any wave that imitates the sinusoidal waveform but has a much larger wavelength is called a harmonic wave and the disturbance it creates in the system is called harmonic distortion. Harmonic frequency currents are created by non-linear devices such as inverters and do not deliver any power to the system. The use of harmonic filters not only improves the power quality but also results in capital and operational savings. The problems associated with harmonics include overheating of neutral wires due to large load currents, interference in the equipment, erratic operation of the control system and relays, poor power factor and over-current surges.

Three kinds of harmonic filters can be used to mitigate these challenges:

  • Passive harmonic filters: These are often connected to individual loads in the plant as they require constant loading to eliminate the harmonic waves.
  • Active harmonic filters: The harmonic current is constantly monitored by active filters and a waveform is generated that corresponds to the non-linear portion of the load. As opposed to passive filters, active filters are able to provide harmonic mitigation under any load conditions.
  • Hybrid harmonic filters: A hybrid filter utilises the properties of both active and passive filters. Therefore, it can mitigate harmonics for variable as well as static loads.

Distributed generation unit

The adoption of off-grid solutions or distributed generation (DG) systems can help reduce the load on grid systems and thus improve the quality of power for customers. With this, the reliability of power, particularly in areas with frequent outages, is significantly improved. This will also be much cheaper as compared to a complete overhaul of the grid and transmission system in the area. The various types of DG technologies include diesel generators, gas turbines, fuel cells, wind turbines and solar photovoltaic systems. DG systems with voltage control capacity can also help avoid voltage fluctuations. However, these can cause harmonics in the system.

Energy storage system

The influx of variable power into the grid due to increasing renewable energy integration and the resultant rise in variable load have led to greater unpredictability in grid operations. This has also caused an imbalance in the production and consumption of power in the system. Energy storage solutions help bridge these gaps by providing power as per the load requirement. They allow the grid to draw power from the storage in case of high demand and store power during low demand periods. Energy storage systems enable quick response to the varying grid requirements, thus maintaining grid stability and high quality power supply.

Smart grid

Being at the core of power supply and transmission, power quality significantly depends on the adaptability and responsiveness of the grid. A smart grid provides a reliable and secure solution to power quality issues in the country. Along with an intelligent network that can balance the varying input and output of power from the grid, monitoring of the power quality is also essential. A smart grid that can procure real-time load data from consumers and all sources of power generation and storage, and has self-healing capabilities and resilient infrastructure will be able to significantly improve the power quality.

Conclusion

With the increasing demand for power in the country, the need for better quality of power is also increasing, especially in the industrial and commercial segments. Better power quality will improve system stability, reduce or eliminate outages and save operational costs of the grid. Thus, to ensure seamless power supply, power quality management measures need to be constantly monitored.

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