Power system operations are becoming more complex by the day with the rapid increase in the number of market players, renewable energy generation, power market operations, ageing infrastructure and synchronisation of regional grids to the national grid. All these factors have put enormous pressure on system operators to maintain grid stability and reliability.
In view of the huge renewable energy capacity envisaged to be added and the associated challenges such as intermittent and variable power supply, there is an urgent need to strengthen and develop the grid interconnections.
To this end, Power Grid Corporation of India Limited (Powergrid), the central transmission utility, and various state utilities have been working towards the strengthening of the transmission system and enhancing grid reliability. Some of the solutions include phasor measurement units (PMUs), static synchronous compensators (STATCOMs), advanced conductors such as high temperature low sag (HTLS) conductors and energy storage systems.
A look at some of the transmission system strengthening solutions and initiatives…
Smart transmission initiatives
As a part of smart grid development, Powergrid has been deploying wide area measurement system (WAMS) based on synchrophasor technology on a pan-Indian basis under the Unified Real Time Dynamic State Measurement (URTDSM) project. Under this project, PMUs are being installed at all substations above the 440 kV level and all generating stations at the 220 kV and above levels. This is expected to facilitate better visualisation and awareness of grid events such as frequency oscillations, voltage instability and system margin, which in turn is likely to enhance the overall grid management.
The URTDSM Phase I project is nearing completion. Almost 1,400 PMUs have been installed across the five regions, of which over 1,080 PMUs are reporting data. For Phase II, Powergrid has requested all participants to submit revised PMU requirements, if any. To meet the communication requirement of URTDSM as well as SCADA upgradation, all the substations of Powergrid, central generating stations and some generating stations of states are being connected to the fibre optic network. In addition, the company is setting up control centres, installing analytical applications for the diagnosis and validation of real-time grid operations and improving grid reliability.
Apart from the URTDSM project, there are several other initiatives being taken to make the grid smarter. These include installing compensation devices such as static VAR compensators (SVCs) and STATCOMs, which would provide dynamic capabilities to the grid. Powergrid has commissioned SVCs at three locations in the northern region and another is under implementation in the northern region. STATCOM has also been commissioned at location in the southern region. Overall, Powergrid is planning to install STATCOMs at 13 locations across the northern, eastern, western and southern regions of the country. As per the Central Electricity Authority, the total investment in compensation devices is estimated at over Rs 28 billion during 2017-22. Further, Powergrid has been using a real-time digital simulator, which is designed specifically to achieve real-time simulation of power systems to study dynamic performance in order to enhance efficiency in operations.
Substation automation
The digitalisation and automation of substations is the ongoing trend to make power systems smarter. Substation automation systems provide advanced disturbance management and event recording capabilities in transmission and distribution networks, resulting in detailed and faster fault analysis. Smart substations are capable of responding to real-time events, enabling faster restoration of faults and ensuring effective asset management. Besides, certain automation solutions can allow the power system to heal itself during emergencies. As a result, there is better grid monitoring and prevention of blackouts. Further, automation solutions for forecasting are useful for identifying a potential grid security threat. This can help utilities overcome grid instability issues in light of the increasing share of intermittent renewable energy sources in the electricity generation mix.
Reconductoring and advanced conductor technologies
Reconductoring refers to the upgradation and strengthening of the existing infrastructure, thereby enabling utilities to augment the quantum and quality of power transmitted through the existing corridors. It also enables utilities to significantly scale down losses and prevent power outages. Further, transmission utilities are using new and advanced designs and technologies in cables and conductors with the objective of reducing the right-of-way (RoW) requirements as well as increasing the current carrying capacity of transmission lines. These include HTLS, gas-insulated lines, high temperature superconductors and cross-linked polyethylene XLPE cables. Advanced conductors carry higher currents while allowing higher temperature ratings and require lower RoW.
GEC
In order to facilitate the transfer of renewable energy from renewable-rich states to other states and absorption of renewable power within the host state, transmission system strengthening is essential at both intra-state and interstate levels. Intra-state transmission system strengthening activities entail the establishment of pooling stations at the 132 kV, 220 kV and 400 kV levels and associated transmission lines. Meanwhile, interstate transmission strengthening mainly comprises the development of high capacity hybrid corridors. Around Rs 400 billion is expected to be invested in transmission strengthening activities under the green energy corridor (GEC) project.
Ancillary services market
Reserve regulation ancillary services (RRAS) were introduced in April 2016 on a pan-Indian basis. Since then, RRAS has provided several benefits such as improvement in the frequency profile of the power system and congestion management. System operators are using ancillary services as a tool to improve grid resilience during low probability, high impact events like outage of large generating stations and extreme weather conditions. RRAS is an additional tool for system operators to ensure grid stability, thereby strengthening the overall power transmission.
BESS
In order to ease congestion in the transmission system, steps such as deployment of battery energy storage solutions (BESS) are being planned. This is the most common energy storage solution that comprises several components such as battery management system, power conditioning system, power transformer and energy management system. BESS itself manages the operations of the battery storage solution by facilitating the charging and discharging of the battery, enables real-time monitoring, and performs optimisation of the entire 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 solutions are also gaining ground.
Other solutions
Other solutions that can be deployed for system strengthening and improving power transmission quality include harmonic filters and constant voltage transformers (CVTs). Harmonic filters are deployed to reduce unwanted harm-onics in the system and enhance the overall efficiency. Harmonic distortions are mainly created in the system by non-linear loads. These loads feed harmonic currents back into the wiring of the equipment, thereby causing system malfunction. A harmonic filter is a combination of capacitors and inductors that are tuned to resonate through a single frequency or a band of frequencies. These filters are used to maintain total harmonic distortions below permissible limits and require constant loading for the elimination of harmonic waves. CVTs neutralise the spikes and electrical noises in the system, mitigate sag and regulate voltage, thereby improving the overall power reliability.
Conclusion
Apart from facilitating power flow from new capacities and meeting the load demand, transmission strengthening also has other benefits. With the strengthening and augmentation of transmission, the total transfer capability or the amount of electric power that can be transferred reliably under a given set of operating conditions, considering the possibility of worst contingency, has increased significantly in India. Further, system strengthening has led to reduction in transmission congestion. The proportion of total electricity generated that could not be cleared due to congestion declined to 0.13 per cent in 2016-17 from 0.3 per cent in 2014-15.
Going forward, the power network and the complexities associated with it are set to grow. Therefore, to ensure optimal grid operations, utilities need to continue taking system strengthening measures.