Power Grid Corp. of India Ltd., (POWERGRID) the central transmission utility of India, has been entrusted with the task of creating a strong and vibrant national grid. The utility carries more than 50% of generated power across the length and breadth of the country. Its transmission system consists of more than 94,000 circuit km (58,409 circuit miles) of transmission lines and 155 ac/dc substations, representing 1.4 million MVA of transformation capacity.
To meet the energy requirements of the nation, large generation capacity additions are envisaged for the coming years. However, most of these generation sources are located in the resource-rich areas — the northeastern and eastern parts of the country — while the load centers are in the northern, western and southern parts of the country. Therefore, to transmit this generated energy to the distant load centers, large power transmission corridors are required.
The task of establishing such a large transmission network requires consideration of socioeconomic and technical challenges that include right-of-way availability, protection of flora and fauna, reduction of transmission losses, control of system fault levels and cost optimization. These challenges can be met, to a greater extent, by employing transmission voltages that are higher than the existing voltage levels of 400 kV and 765 kV. Transmission at a higher voltage can offer huge advantages in terms of increased power-transfer capacity per unit right-of-way, reduced transmission losses and reduced environmental impact.
The Need for Higher Voltage Levels
Previously, the Indian power system operated in asynchronous mode. Today, the country's four major power regions — northeastern, eastern, western and northern — operate as one synchronous grid at the same frequency. At present, the southern region's grid is connected to the synchronous grid in asynchronous mode through high-voltage direct-current (HVDC) links, but it is planned for synchronization by 2017.
The backbone transmission system in India operates mainly at 400 kV ac. Very few circuits at 220-kV and 132-kV ac levels are in operation in the northeastern part of the country. In 2007, POWERGRID commissioned its first 765-kV ac line. Today, the utility owns and operates about 4,000 circuit km (2,486 circuit miles) at 765 kV. Bulk power transfers over long distances are carried out through the HVDC system, operating at the ±500-kV voltage level.
National Test Station
In a bid to boost its transmission capacity, India has moved toward ultrahigh-voltage (UHV) ac voltage levels for power transmission. Since this technology has not been commercially available worldwide, the Indian electricity industry joined forces for the indigenous development of this technology. To achieve this objective, a 1,200-kV UHV national test station is being established under a unique model of public-private partnership by POWERGRID in association with Indian equipment manufacturers and the Central Power Research Institute. POWERGRID is creating the necessary infrastructure for the test station, whereas 35 Indian manufacturers have come forward to develop 1,200-kV equipment at their own cost.
The 1,200-kV national test station is geographically located in the heart of India — in a town name Bina, in the state of Madhya Pradesh. The test station consists of two 1,200-kV bays and a transmission line — one single-circuit line 1.1 km (0.68 miles) in length and one double-circuit line 0.8 km (0.5 miles) in length — with a nominal voltage of 1,150 kV and a maximum operating voltage of 1,200 kV. Power flow through the test station is planned through the Satna-Bina-III 400-kV transmission line.
Uniqueness of 1,200 kV
The 1,200-kV system parameters were determined after simulation and field studies were undertaken and not as a result of extrapolation from the 400/765-kV systems. POWERGRID undertook various studies and tests to determine the configuration of the 1,200-kV transmission lines and switchyard. Equipment parameters were finalized by working groups comprising experts from POWERGRID and the participating equipment manufacturers. Also, POWERGRID appointed a panel of international consultants for expert guidance.
To realize the best design technically and economically for the transmission line and substation, important solutions for network problems specifically suited to the requirements of the UHV system were introduced. These included insulation coordination with optimized insulation levels, high-performance multi-column surge arresters and dead-tank circuit breakers. These sophisticated technologies resulted in the realization of highly reliable and economical UHV substation and transmission lines as well as the optimization of the size of UHV equipment.
The Next Phase
To date, POWERGRID has established one 1,200-kV bay, single-circuit line and double-circuit line for the test station. The Indian manufacturers have developed major equipment (for example, transformer, surge arrester, capacitive voltage transformer, circuit breaker, bus post insulator, substation and line hardware) and factory tests have been performed. Following the on-site acceptance tests of the equipment, the 1,200-kV bay and line were charged at 1,200 kV.
Construction activities and equipment development for the next phase of the project are ongoing, and when the test station is fully commissioned, the 1,200-kV equipment will be loaded through 400 kV. The single-phase 400/1,200-kV auto-transformer bank from the first phase setup will step up the voltage from 400 kV to 1,200 kV. The power flow will be through the auto-transformer bank to the 1,200-kV bay, then to the single-circuit line and, subsequently, to the double-circuit line through interconnection of the single- and double-circuit lines. Also, the double-circuit line will be terminated at the 1,200-kV bay and the voltage will be stepped down to 400 kV through the single-phase 1,200/400-kV auto-transformer bank.
The test station equipment will then be kept at the maximum operating voltage for a prolonged period. Various field studies and measurements will be carried out on the lines and substation equipment. These studies and tests will help to optimize the 1,200-kV system and equipment parameters. The field test program will help to establish safety, quality and operational requirements for UHV technology in addition to paving the way for developing field-proven UHV equipment.
A 1,200-kV single-circuit transmission line from Wardha to Aurangabad, in the western part of the country, is currently under construction. Initially, the line will operate at 400 kV; at a later date, it will be upgraded to 1,200 kV. Additional 1,200-kV transmission lines are in the planning stage.
By 2020, the total generation capacity of India will increase from the present installed capacity of 202 GW to 480 GW. To achieve this substantial growth and balanced regional development, the capacity of the power-transfer system needs to be integrated across the entire country. This necessitates the development of a large transmission network, which reduces the required right-of-way per-unit power transfer with minimal environmental impact. The 1,200-kV test station project is key to the development of India's electric power transmission system, as the technologies that will be proven will ensure a reliable and dependable power supply for India's continuing and accelerated development.
With the commissioning of the first phase of the 1,200-kV national test station, India has attained the world's highest transmission voltage level. The event undoubtedly represents the most significant international achievement in UHV power transmission. Establishment of this 1,200-kV national test station has given Indian manufacturers an opportunity to develop indigenous capabilities in the design and manufacture of UHV system equipment at a voltage level for which there are currently no international technical standards.
I.S.Jha is director of projects for Power Grid Corp. of India Ltd. He previously served as executive director of engineering for the company, as well as executive director of corporate monitoring and regional executive director of the northeastern region. Apart from these functions, he was a lead member in planning, engineering and execution of APDRP and RGGVY schemes in Power Grid.
S.K. Agrawal ([email protected]) is the executive director of the technology development of Power Grid Corp. of India Ltd. With more than 36 years of experience, Agrawal's major contributions include design, engineering, quality assurance, construction, operation and maintenance of 400-kV, 800-kV, ±500-kV high-voltage dc substations and the 1,200-kV ultrahigh-voltage ac national test station. He has made significant contributions in developing international standardization in quality management as a member of Working Group TC 176 (ISO 9001) and as a member of CIGRÉ Working Group B3.29 on field tests technology on UHV substation during construction and operation.
B.N. De Bhowmick ([email protected]) is an additional general manager in the technology development of Power Grid Corp. of India Ltd. With more than 28 years in the power sector, he has made contributions to engineering, commissioning, operation, maintenance and condition monitoring of transmission assets. As a member of an expert group on transformer condition monitoring and dissolved gas analysis in POWERGRID, he has published several papers on subjects including 1,200 kV and transformer condition monitoring.
S.B.R. Rao ([email protected]) is chief manager in the technology development of Power Grid Corp. of India Ltd. His major contributions include the development of the 1,200-kV national test station in India in association with a large number of leading Indian manufacturers of transmission system equipment, which resulted in indigenous development of 1,200-kV ultrahigh-voltage ac technology in India. He also has contributed to the design and engineering of the supervisory control and data acquisition, energy management system, distribution management system and communication systems for the unified load dispatch and communication system.
Akhil Sundaran ([email protected]) is an engineer in the technology development department of Power Grid Corp. of India Ltd. His present area of work includes development of systems and technologies for improving power transmission efficiency. Sundaran has contributed significantly to the development of the 1,200-kV national test station in India. Earlier in his career, he had the opportunity to be associated with the operation and maintenance of electrical equipment in the petrochemical industry, including work on the execution of city infrastructure development projects.
Indian Transmission Network Statistics
Power Transmission Capability of Various Levels
Central Power Research Institute | www.cpri.in
Power Grid Corp. of India | www.powergridindia.com