In the past, Indian power utilities have mainly focused on meeting the demand-supply gap. However, in view of the government’s target to provide 24×7 quality electricity to all by 2022, they are now looking beyond availability and towards quality. Power quality (PQ) can be defined as the consistency of power supply. It can be quantitatively measured in terms of voltage, current and frequency deviation of the electricity supply that can cause failure in the equipment. Reasons for poor PQ can be involuntary (such as lightning, equipment failures, faults and flashover); or forced (such as voltage distortions and notches). PQ problems may happen due to non-linear loads, unstable power system, large machines, etc.
Impact of poor power quality
An average household uses several types of electricity-powered equipment for heating, lighting, communication, entertainment, etc. PQ fluctuations can result in the malfunctioning of the equipment or may even cause permanent damage.
PQ problems such as voltage dips, spikes, harmonics and interruptions can have serious implications for industrial consumers. Industries use sensitive electronic equipment, and the addition of non-linear loads and renewable energy grids can raise PQ concerns for them. Even if the fluctuations last for less than a second, the damage due to PQ issues can be permanent. It can disrupt everyday activities and operations. In a worst-case scenario, it might pose a severe risk to the safety and reliability of power systems.
Some specific problems faced due to PQ issues are computer lockups and data loss due to the malfunctioning of IT equipment, which are sensitive to voltage fluctuations; fluctuations, which have caused total equipment damage; extra heating, premature ageing and decreased operational efficiency of motors and process devices; nuisance tripping of protective devices like relays, circuit breakers and contactors; noise interference to telecommunication lines; and flickering, blinking and dimming of lights.
Power utilities also face challenges due to PQ issues. Problems such as unbalanced operation and harmonic currents cause extra losses in the system. Overvoltages result in additional stress to the insulation. Often, the utilities derate their equipment to ensure safe operation, but this reduces equipment capacity, leading to suboptimal utilisation.
Technology solutions to tackle PQ problems
The mitigation of PQ problems may take place at different levels – transmission, distribution and end-use equipment.
The steps that can be taken to achieve power factor improvement are mitigation of voltage sags/swells, fluctuations/flickers, and over/undervoltage conditions; reduction of voltage interruptions; and mitigation of transients, voltage notches and harmonic/inter-harmonic distortions. Other solutions, both corrective and preventive, include the use of enhanced devices (both interface and end-use).
The specific technological improvements that can be implemented include the use of series capacitors, which can compensate the inductance of long transmission lines to improve voltage regulation; shunt capacitors to control voltage and correct the power factor; static var compensators (SVRs) to provide fast reactive power compensation in power systems through a combination of capacitors and reactors to regulate the voltage; and static synchronous compensator (STATCOM), a shunt device to improve transient stability on electrical power networks by controlling the power flow. Further, the distribution static compensators, a fast-response, solid-state power controller that improves the power quality at the point of connection to the utility distribution feeder. Also, dynamic voltage restorers (DVRs) can be deployed to mitigate problems of spikes, surges, flickers, sags, swells, notches, etc. in the voltage.
A unified power quality conditioner, a custom power device to mitigate voltage- and current-related issues, is another solution. Harmonic filters can be used to remove the problem of harmonic waveform distortion. K-Factor transformers can be used for non-linear or harmonic generating loads, which cannot be handled adequately by a standard transformer. Transient voltage surge suppressors (TVSSs) can be used to protect equipment from high voltage surges caused by lightning and switching of inductive or capacitive devices. Also, the isolation transformer, a special type of transformer that electrically isolates people and equipment from the hazards of PQ problems such as transients and high-frequency noise, can be used.
Role of energy storage systems
Grid codes and regulations are imposing some new and stringent technical requirements for the integration of renewable power into the grid. These technical requirements are enforced to guarantee that no bad quality of power is injected into the grid. Energy storage systems can be used to provide electric loads with a ride-through capability in poor PQ environments. Energy storage systems improve the grid regulation by smoothening the power output from renewable energy sources, help in peak shaving of demand, and increase the reliability of large-scale renewable energy grid-connected systems and off-grid systems without diesel backup. When the output power from the renewable energy plants is fluctuating, battery energy storage systems give both real and reactive power support to the grid and maintain the grid voltage profile. Battery energy storage systems reduce the voltage sags caused by faults or switching of large loads in the system, and reduce the peaks in power demand.
Proper technical measures and strategies can help address power quality issues and maintain grid stability. Apart from this, there is a need to frame regulations, implement them and monitor them to achieve the goal of 24×7 quality power supply.