Driven by the three imperatives of combating climate change, providing affordable energy to consumers and ensuring security and independence of energy supplies, World is moving towards the creation of a single market in electricity. Super Grid can be the possible solution.
A super grid is a wide area transmission network that makes it possible to trade high volumes of electricity across great distances.
It is sometimes also referred to as a ‘mega grid.’ Super Grid has imposed two senses on current usage – the first one being a super structure imposed upon existing grids and the second one is the ability to possess some characteristics exceeding those of even the most advanced grids.
Technology
A super grid utilises the Three Phase AC technology of 50 Hz (AC Grids) with voltages such as 400kV, 750kV, 1000kV. It is also modeled for Three Phase AC technology with reduced frequency in AC Grids. HVDC transmission is also possible in super grids. The power transfer equation is given by:
Features
Super grids are characterised by:
- Flexibility in system balancing
- High capacity for bulk power transmission
- Geographically long distances
- Extensive use of Hybrid Systems (HVDC, FACTS), which improves the system stability
Structure and components
The super grid structure represents the integration of various renewable energy resources into a single power utility that can feed a no. of loads connected to the system.
Fig. 1: European Super grid… (earthtimes.org)
Certainly, all the generation points are connected with this grid. High capacity transformers, HVDC transmission lines and back-to-back converters are the most important components. Also, smart indication and protection equipments satisfy the security system of the grid.
The implementation of such an interconnection highlights the need for new operational standards to ensure that the reliability of the interconnected systems is improved and the frequency-control reserves are shared among the power systems.
Fig. 2: 650MVA Transformer used in Super Grid Transmission at Al-Zour substation (T&D World)…
This gives rise to a balancing reserve generation capacity and the harmonisation of policies and practices. The HVDC converter station ensures that a large power reserve is available in case of a severe disturbance on either side of the 50 and 60-Hz networks.
Fig. 3: 400kV lines at Ghunan substation… (T&DWorld)
Steady-state analysis and dynamic studies were conducted to identify the limits of such joint interconnected operation, and to give guidance to procedures and sequences that ensure safe and stable operations.
Fig. 4: Back-to-back HVDC converter station… (T&D World)
The HVDC converter station is generally designed for two operational modes.
- The economic dispatch mode allows stable commercial exchanges with no frequency control
- The Dynamic Reserve Power Sharing (DRPS) mode provides automatic fast power transfer and mitigates generation deficiencies by mobilising DRPS between the 50Hz and 60Hz systems. The activation of the DRPS mode is dependent primarily on two criteria, namely, the rate at which the frequency changes or the rate at which load is lost. These events are governed by the load on the interconnector and the time or season at which these events occur.
Thus, the HVDC converter station offers a significant capability of emergency reserve sharing between the 50Hz and 60Hz systems, thus contributing to the stabilisation of the systems after large disturbances.
Implementation in Indian sub-continent
- Shortage of coal at Coal based generating plants
- Refining and extraction of coal does not match the coal utilisation factor of the plants
- Import of gas not a feasible option
- Renewable energy resources far from the load centres
Fig. 5: Electricity generation from different sources (2011)… (Farhan Beg 2014)
Scope of super grid deployment
- Large potential for tapping renewable energy is available in the Indian subcontinent. But, the sources are not in immediate proximity to load centres
- There is a strong need to integrate the renewable energy into the existing electricity grid to: 1) Curb the energy shortages, 2)Improve quality of electricity, 3)Regulate the price of electricity
Energy transfer locations
Fig. 6: Energy transfer from generation side to load side… (Farhan Beg 2014)
Supergrid modelling
- Provide an electricity highway for the flow of electric power between nations
- Provide a capability to interconnect the asynchronous transmission systems of the subcontinent
- Efficiently control the exchange of seasonally varying production and storage capacities
Fig. 7: Proposed model of super grid… (Farhan Beg 2014)
HVDC converters
As far as HVDC connections are concerned, multi terminal DC connection with a possibility of both series & parallel combinations are adopted.
Fig. 8: HVDC converter arrangement…
Future developments
The following developments can be made, in addition to the above mentioned to fully utilise the potential of super grid:
- Further development of far shore bulk power wind parks having a capacity of 1000 Mega Watt.
- Continuous phasing out of coal fired and nuclear power plants
- Balancing generation and load calls for stronger system integration
- To achieve the required flexibility of power flows and facilitate power trading, offshore wind parks are connected to one another and tapped into cross country links
Fig. 9: Proposed experimental super grid model for India…
The system integration process is continued leading to a wide overlay grid. The overlay grid, mainly based on DC, is built to interconnect wind parks and pumped hydro storages – as well as large scale solar power plants all across the country.
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