Substations are critical components of the power system as they provide protection, control and stability to the entire system. Over the past few years, the number of substations installed in India in the transmission and distribution segment has increased exponentially. While there has been growth across all voltage levels, substations are increasingly being installed at the ultra high voltage levels of 500 kV and 765 kV. Substation automation technologies are also fast gaining importance as managing grid operations has become challenge owing to rapid network expansion and increased complexity.
Substation growth
According to the data tracked by Power Line, central and state sector transmission utilities owned and operated more than 7,360 substations at voltage levels of 66 kV and above at the end of 2014-15. During the period 2010-11 to 2014-15, the number of installed transmission substations registered a high compound annual growth rate (CAGR) of 8.5 per cent, driven by growth in the interstate transmission system (ISTS). Meanwhile, substation capacity increased from 345,513 MVA at the end of March 2011 to 582,600 MVA at the end of March 2015, registering a CAGR of 13.9 per cent.
This growth is expected to continue in the coming years. According to the Perspective Transmission Plan for Twenty Years (2014-34) published by the Ministry of Power, the substation capacity at the 400 kV and 765 kV levels will increase by 194,000 MVA during the Twelfth Plan period (2012-17) and by another 128,000 MVA in the Thirteenth Plan period (2017-22).
In terms of voltage, a large number of transmission substations in the intra-state system are at the 66 kV and 132 kV levels. As of March 2015, of the 7,125 substations owned and operated by state transcos, 32 per cent were at the 66 kV level, 32 per cent at the 132 kV level, 16 per cent at the 220 kV level and 2 per cent at the 400 kV level. In contrast, the share of high voltage substations is higher in the ISTS. Of the 192 substations operated by Power Grid Corporation of India Limited (Powergrid) as of end-March 2015, 138 substations are at the 400 kV, 22 at the 765 kV, 11 at ±500 kV HVDC, 11 at the 220 kV, and 10 at the 132 kV levels.
In the distribution segment, data tracked by Power Line estimates that nearly 3.75 million substations are operational at the 33 kV level and below across 42 utilities as of March 31, 2015. The number of substations has increased at a CAGR of 10.9 per cent over the past five years. To achieve the substation capacity targeted to be added over the next five years, the number of substations is expected to increase to 6.4 million in 2019-20, at a CAGR of over 11 per cent.
Substation automation
As a result of rapid expansion of the power system in terms of size and complexity, substation automation technologies are gaining importance in order to ensure efficiency, security and reliability of the power system. Substation automation was introduced for intelligently managing grid operations. It allows continuous monitoring and control of various substation components from a remote location. It also enables users to lower operational costs by reducing the manning needs at substations. Moreover, the use of smart devices helps the industry enhance predictive maintenance and planning. This ensures reduced asset downtime, faster restoration of faults and effective asset management.
Substation automation entails integrating the protection, control and data acquisition functions into a minimum number of platforms to reduce capital and operational costs and panel and control room space requirements and eliminate redundant equipment and databases. Substation automation helps in managing and controlling various components of a substation from a remote location. Some of the key components of substation automation are intelligent electronic devices (IEDs), communication networks and supervisory control and data acquisition (SCADA) systems, which are used to control devices and acquire and transfer data. IEDs are devices that incorporate one or more processors that have the capability to receive or send data from or to an external source. Some of the IEDs are digital relays, smart meters, reclosers, digital transducers, programmable logical controllers, capacitor bank controllers and load tap changer controllers.
The deployment of IEDs and SCADA systems requires strong support from an effective data communication system for real-time data transfer. In the case of conventional substations with legacy communication, serial communication buses or proprietary communication media are used along with associated protocols. Meanwhile, in substations with modern communication, data transmission takes place within and between the station, bay and process levels. Various communication protocols, including Ethernet-based IEC 61850 as well as vendor-specified Modbus, Ethernet IP, DNP3 and IEC60870-5-104, have been used at the utility level for substation automation systems.
Progress in India
Powergrid introduced the concept of substation automation in India in 2003, when its first remote-controlled 400 kV substation was established at Bhiwadi in Rajasthan. Today, all new substations set up by the company are being provided with automation technologies.
In April 2015, Powergrid commissioned the National Transmission Asset Management Centre (NTAMC) at Manesar in Haryana, comprising SCADA systems, remote accessibility systems and video monitoring systems. Built at an investment of Rs 1.95 billion, the centre enables centralised monitoring, operations and management of all substations, and remote operations and management of transmission assets. Following its commissioning, 82 substations are now being remotely operated from the NTAMC, including 36 substations without an operations team. Powergrid is currently in the process of setting up nine regional transmission asset management centres.
Under the Unified Real Time Dynamic State Measurement (URTDSM) project, Powergrid is implementing the wide area measurement system (WAMS) on a pan-Indian scale, which will include the largest deployment of phasor measurement units (PMUs) globally. WAMS will ensure dynamic observability and better monitoring of substations through data reporting at 25 samples per second, unlike SCADA where this is done once every 10 seconds.
Prior to the roll-out of the URTDSM, Powergrid had initiated a WAMS pilot project under which 64 PMUs were installed, including three by independent power producers. The available data is being analysed at the National Load Despatch Centre (NLDC). The URTDSM project is being implemented in two phases. Phase I includes the installation of more than 1,100 PMUs at 351 substations and generating stations of the ISTS and intra-state transmission system connected through an optical ground wire (OPGW) network; the installation of phasor data concentrators (PDCs) at the NLDC, regional load despatch centres, state load despatch centres, and the NTAMC; and the development of analytical software by the Indian Institute of Technology, Mumbai. The second phase of the project includes the installation of 554 PMUs at substations and power plants, 11,530 km of OPGW and associated works, and a WAMS-based protection system.
The design of the URTDSM project has been finalised by Powergrid. The survey for PMU locations including substations and generating stations and control centres for PDCs has also been completed. Progressive testing is being done for PMUs, and despatch has started. In addition, Powergrid is implementing a state-of-the-art process bus technology using novel sensors such as optical instrument transformers for substation automation based on the IEC61850 protocol. At present, the company operates an optic fibre network of about 25,000 km. Over the next two to three years, it plans to replace its existing microwave hops with 20,000 km of OPGW and add another 20,000 km of OPGW for connecting its substations. For implementing SCADA, the utility plans to deploy power line carrier communication links between 132 kV and 66 kV substations and area/state control centres, and very small aperture terminal links to connect important remote stations and control centres.
While Powergrid is leading technology adoption in substation automation, other public and private utilities at the state level have also taken a number of initiatives in this direction. For instance, Karnataka Power Transmission Company Limited has installed a statistical analysis system at 24 of its 220 kV substations to control and monitor substation equipment from both remote and local control centres. Mean-while, Tata Power has adopted power system protection components based on the IEC 61850 standard for its substations. The company has implemented digital protection signalling based on generic object-oriented substation event messaging, which has eliminated the use of hard-wired cabling, thus improving reliability.
Conclusion
The number and capacity of substations deployed in India have increased significantly over the past few years. Going forward, technological advances across various domains of substation automation systems will play a significant role in determining the pace and direction of smart grid deployment in India. At present, despite the operational advantages, utilities, particularly in the distribution segment, face challenges in implementing such solutions due to a demand for huge initial investments and existing regulatory issues. Therefore, the utilities need to play a proactive role in defining their automation requirements and selecting the right technology or solution from the plethora of options available in the market.