A systematic overhaul of India's power grid5 April 2002
In January one of the world's largest and most complex transmission network control systems was officially inaugurated by India's prime minister Atal Bihari Vajpayee. Designed and installed by Alstom, it covers PowerGrid's entire Northern region. It is the first stage of a project to bring the entire Indian grid under a national hierarchy.
The power system supplying the sub-continent of India has experienced a phenomenal rate of growth over recent years. Installed generating capacity has rocketed from 1 362 MW in 1947 to the present total of over 100 000 MW. The transmission infrastructure has undergone significant expansion involving the 400 kV and 220 kV networks across the entire country.
Planning, operation and control of the bulk power supply system in India is based on five regional grid networks: Northern, Southern, Western, Eastern and North Eastern. Each regional grid comprises a number of independent generators and power system operators, including state electricity boards and other power utilities.
In spite of the extensive growth of the electricity supply system throughout India, investment in new generating capacity has never kept pace with demand, leading to a continuing shortfall. Nevertheless, the Indian government is firmly committed to an energy strategy aimed at increasing the overall capacity of both the generation and transmission systems to 180 000 MW to meet projected demand over the next 15 years.
In addition to major national investment to increase generation and T & D capacity, it has also become essential to manage the grid operation effectively and on a real-time basis to ensure that power demand can be met under all conditions and that energy is available at minimum cost through optimal utilisation of resources and merit order operation. More effective network management also means that supply quality, particularly with regard to frequency, voltage, and reliability, is maintained at consistently high levels.
With the rapid growth and vast geographic spread of the supply system throughout India, the operation and management of an integrated power network based on both regional and national grids has become complex and challenging. It has led inevitably and with increasing urgency to a requirement for real-time monitoring and control of all central and state-sector generation and transmission utility operations. This in turn has necessitated the total modernisation of existing load dispatch and communication (LD&C) facilities to provide consumers with high-quality power economically, reliably and securely. Accordingly, in 1992, the Indian government transferred responsibility for implementing nationwide LD & C facilities to the Power Grid Corporation of India Ltd (PowerGrid).
With its role as central transmission utility of India, PowerGrid has overall national responsibility for power transmission and for balancing intra- and inter-regional power demand and supply. The corporation is tasked with installing, operating and maintaining the EHV AC and HVDC transmission systems including load dispatch facilities under the Central Sector, with responsibility for the regional and national power grid networks. The state-owned organisation is one of the largest transmission utilities in the world, with some 40 per cent of India's total generated power being carried nationwide on the PowerGrid transmission network over a total distance of about 40 000 circuit-kilometres.
In order to manage and operate India's complex transmission network efficiently over the huge distances involved, PowerGrid created five geographic regions covering the entire country. With the increasingly urgent need for real-time grid management and economic power dispatch, the transmission utility has now undertaken the phased implementation of unified load dispatch and communications (ULDC) schemes for each of the grid networks in these five regions. In each region, the generation, transmission and distribution of power is organised along state lines, with state-owned power systems and load dispatch centres operated by state electricity boards. These SEBs together with the Central Sector group are referred to as 'constituents'. The constituents in the Northern region include Himachal Pradesh (HPSEB), Haryana (HSEB) Jammu & Kashmir (J&K), Punjab (PSEB), Rajasthan (RSEB), Uttar Pradesh (UPSEB), Bhakra Beas Management Board (BBMB), Delhi Vidyut Board (DVB ) and the Central Sector (CS).
The scheme will ultimately establish a national load dispatch centre to supervise real-time grid operation at national level, improving system security, availability and reliability, minimising supply disturbances and transmission failures. The complex ULDC schemes, the first of their kind in the world, are being implemented at an estimated cost of over 22 billion Indian rupees (¤524 million) funded by a variety of multilateral agencies including the World Bank, the Asian Development Bank and the European Investment Bank, among others.
First ULDC scheme
India's first ULDC project was designed, supplied and installed by Alstom's energy management and markets (EMM) business, part of the company's transmission and distribution division which specialises in the development and integration of real-time power control systems, energy management systems and telecommunication products.
Under a ¤40 million contract, Alstom has successfully completed a state-of-the-art, on-line monitoring and control system for the Northern regional power network, which extends over an area of one million square kilometres and includes no fewer than ten regional utilities. The ground-breaking project comprises supervisory control and data acquisition (SCADA) and energy management systems, together with a dedicated telecommunications infrastructure, providing a facility for the management of the transmission grid in real-time and for the economic dispatch of an available capacity of 20 000 MW. The SCADA and EMS systems are configured in a three-level hierarchy, with a regional power control centre in Delhi, a state load dispatch centre at each of a total of eight SEBs and supply utilities, together with an additional 24 sub-load dispatch centres.
To ensure that such a large-scale project could be completed within the required time schedule, Alstom adopted a 'unified' approach for planning, engineering, procuring and implementing the load dispatch system. Although it is quite common for major project start-ups to be subjected to delays of anything up to three years for the planning process alone, this undertaking was completed successfully in the record time of just 42 months from the start of physical activities, despite its unique size and complexity.
The chosen approach offered a number of significant benefits, including tightly co-ordinated and phased implementation, the installation of LD&C facilities within the region in the same time-frame, and compatibility of hardware, software and communication equipment. All computer-based systems were standardised, spares, training and maintenance facilities have been optimised and operational expertise developed under this single, unified approach. As well as implementing the regional schemes in close association with both the state power utilities and other regional organisations, PowerGrid's strategic plans also include the provision of a national load dispatch centre, monitoring the power system at national level.
The Alstom/PowerGrid ULDC scheme for the Northern region, which became operational in January 2002, has involved modernising and upgrading the entire supervisory and control infrastructure and has included the provision of a dedicated regional communications system. As the Indian power supply network is operated on an hierarchical basis, a similar hierarchical approach has been adopted for the new load dispatching scheme. The pyramidal structure is configured with the national load dispatch centre and regional LDCs at the apex, supported by sub-LDCs and state LDCs at an intermediate level. The 33 centres are supported in turn by a total of 369 remote terminal units (RTUs) located strategically at generating plants and substations, representing the lowest level.
The RTUs capture and transmit digital and analog data on network parameters such as status of circuit breakers, voltage, frequency, reactive and non-reactive power to the appropriate Sub-LDC, state or regional LDC in real-time. The data is computer processed and analysed, providing the network controller with relevant operational instructions to carry out assigned functions at each level. The SCADA/EMS systems are based on distributed architecture incorporating open system features. This open, modular configuration has been designed to allow for future expansion of the network system in terms of hardware as well as in application software, to meet increasing power demand.
The EMS software design is based on Alstom's 'e-terraplatform' energy management platform, which supplies one-time capability at the lower layers in the system. This approach provides a number of specific benefits, including greater general functionality available across all applications with less code to write and maintain at the application layer. At the same time, services are implemented more consistently across applications and interfaces between applications are improved and made more consistent.
The three-tier hierarchical operating system consists of an application layer, a real-time control system environment (RCSE) layer and the operating system layers, with the operating system at the lowest level. The OpenVMS operating system, including language compilers, linkers, graphical user interface support and communications protocols, such as DECnet and TCP/IP, is used for all servers that support the energy management platform. The second-tier RCSE layer provides the necessary system support functions, which include database management ('e-terrahabitat') together with utility configuration manager and back-up programmes ensuring high availability (CFGMAN). User interface tools, communications software and utility libraries are also included. The third-tier application layer includes the major SCADA, generation and network subsystems, which are designed to implement the EMS. The utility subsystem (RCSE) provides services to the other subsystems such as alarm and user interface functions, although the majority of the utility software in the e-terraplatform is, in effect, part of the RCSE layer.
The EMS application layer consists of three principal real-time subsystems. The SCADA subsystem acquires real-time data from the RTUs and other communications sources to provide centralised control. The generation subsystem is designed to control energy production, meeting demand and transaction commitments while at the same time minimising generation costs, issuing the necessary command instructions to the generating units via the SCADA subsystem. The network subsystem operates in real-time to model the power transmission system, using the transmission network branch topology and voltage to compute bus voltages and current flow. The operations scheduling subsystem forecasts load generation and interchange for use by real-time generation and network applications and an historical information management subsystem provides real-time data sampling and subsequent storage in a relational database. A simulator subsystem covering the entire power network has also been provided for dispatcher training purposes.
The Northern region ULDC scheme has been implemented in close association with the eight state electricity utilities, together with other relevant generators and suppliers. Nodal centres are located at: New Delhi for the Northern region, Shimla (Judog) for Himachal Pradesh, Lucknow for Uttar Pradesh, Minto Road for Delhi, Panipat for Haryana, Chandigarh for BBMB, Patiala for Punjab, Gladni for J&K, Rishikesh for Uttaranchal and at Heerapura for Rajasthan.
The most basic initial function of state-level load dispatch operations, which are aimed ultimately at matching available power generation capacity with the demand-load, is that of operational planning. Providing a platform on which all other monitoring and control processes are based, operational planning includes functions such as demand forecasting, generating plant scheduling, load shedding and restoration scheduling. Under the ULDC project, specially designed software programmes such as 'Load Forecasting' ('e-terraloadforecast'), 'Inflow Forecasting' - a programme designed specifically for hydro generating stations - 'Transaction Scheduling' ('e-terraschedule') and 'Resource Scheduling and Commitment' ('e-terracommit') have been provided to assist the operator in this initial planning phase. The 'Resource Scheduling and Commitment' program is designed to provide the best operating scenario in terms of cost while maintaining security of supply, over the entire advance planning period from a single day up to a full week. The imbalance between planned power flows and actual operating conditions is subsequently monitored and controlled through a separate 'automatic generation control' (AGC) function. The AGC operates in conjunction with other programmes such as 'reserve monitoring', 'load shed support', 'economic dispatch' and 'security enhancement' to monitor continuously both the network load level and the generated power output. The control system has inbuilt features to issue commands automatically to selected generators to increase or decrease the power output from their plants, and advises operators to shed or restore load as necessary. The system currently requires command instructions to be followed manually to maintain the network in balance, but as operator confidence in the software-driven system increases over time, network power control will become an increasingly automatic, closed-loop function.
At the regional level, the EMS/SCADA system is designed to co-ordinate the regulation and control of power flows, while at the same time optimising scheduling and dispatch functions within the region. The RLDC operator is able to monitor and maintain network supply security through real-time network analysis, using specifically designed software programs such as the 'network status processor' and the 'state estimator'. These programmes provide a consistent data-set for contingency analysis, security enhancement and optimum power flow to assess the security of the power supply network in real-time, providing advance warning of possible unstable network operating conditions, and alerting operators and supplying advisory details of any remedial action that may be required.
Additional 'post operational analysis' software programs, such as that for production costing, are also built into the system. These serve to provide the actual costs of a specific operation for comparison with the 'optimal' cost, which can serve as a benchmark for continual improvement.
Following successful implementation of the project described here, Alstom is installing similar EMS/SCADA schemes in a further two regions. A ¤13 million scheme covering PowerGrid's North Eastern region is now under way and will comprise eight control centres and 66 RTUs. Under a subsequent
¤24 million contract awarded last year, the company is also installing a new system in the Eastern region comprising 15 control centres and 179 RTUs. In India's Southern region, Alstom is supplying a digital microwave telecommunications network which will provide a dedicated voice and data-communications facility linking control centres and sub-stations throughout the region. The network is spread across 70 sites, covers 600 000 km2 and supports 1000 channels.
The effectiveness of the new high-technology power management and control system was demonstrated just days before the Northern region ULDC was officially inaugurated, when the high-speed EMS/SCADA facilities at the new load dispatch centre were brought into operation, averting total power network collapse. The previous year, a series of faults and cascade-tripping had resulted in a complete outage of the entire regional supply network, the 24-hour blackout causing an estimated loss to the economy of 5 billion Rupees, or ¤119 million. In the latest event, a combination of severe weather and high power demand had caused continual circuit-breaker tripping, eventually leading to the loss of the main supply-line from Agra. According to R. P. Singh, chairman of the PowerGrid Corporation, a potential crisis at least as severe as that of the previous year was avoided. Work continues in extending the system to include other regional networks.