The transmission grid in India has witnessed significant changes such as grid integration, increasing renewable power generation and power market strengthening over the past few years. This has led to the demand for a sophisticated data management and analysis system. The Unified Real Time Dynamic State Measurement (URTDSM) project is one such initiative by Power Grid Corporation of India Limited (Powergrid). It aims to enhance situational awareness and visualisation of the power system on a real-time basis, thereby improving grid control as well as enabling stronger emergency resolution.
The project employs wide area measurement system (WAMS) technology to collect data on grid parameters like voltage and current magnitude, and angles. WAMS consists of four elements – phasor measurement unit (PMU), phasor data concentrator (PDC), and communication network and analytical software. PMUs are devices that use a common time source for synchronised data collection on voltage and current magnitude, frequency and its rate of change, and phase angles. This information is relayed to PDCs, which synchronise synchrophasor data from multiple PMUs via a fibre optic communication network. PDCs further send this syncrophasor data to state load despatch centres (SLDCs), which in turn send it to the five regional load despatch centres (RLDCs). From there, the data goes to the super PDC at the national load despatch centre (NLDC) and is backed up. Finally, the data is fed into analytical software whose functions include vulnerability analysis of relay, development of dynamic/linear state estimator, on-line circuit validation test (CVT) parameter validation, development of a supervised zone 3 distance protection scheme to prevent unwanted tripping, emergency control schemes for controlling frequency and voltage instabilities, and schemes for providing out-of-step protection and adaptive islanding.
The PMUs report data at the rate of 25 samples per second whereas the supervisory control and data acquisition (SCADA) system collects data only once every 10 seconds. Thus, a frequency difference arising during a transient and lasting for a fraction of a second would be captured by PMUs, but not by a SCADA system. The WAMS technology also helps in determining stress in the grid by measuring phase angles across nodes, carrying out forensic analysis of faults and grid incidents, analysing grid operations post despatch and facilitating efficient calibration of the measuring equipment. This technology also provides more intelligent and dynamic information to special protection schemes designed to develop self-healing grids.
Thus, WAMS data would be of utmost importance when planning for the power system in the country. It would enable synchronous measurement of real-time grid parameters across the widely spread national grid, resulting in reliable, secure and economical grid operation.
Project implementation plan
The URTDSM project roll-out was preceded by a WAMS pilot project in the northern region from April 2010 to May 2011. PMUs were installed across eight substations in the region. Following this, WAMS pilot projects were initiated in all the other regions and a total of 64 PMUs were installed.
Under the URTDSM project, the WAMS technology will be implemented in two phases. Phase I will entail technology implementation in two stages – stage one covering the northern, eastern and north-eastern regions, and stage two covering the western and southern regions. It would include the installation of around 1,100 PMUs at 351 substations/ generating substations, including 400 kV stations in the state and interstate transmission system (ISTS) grids, 220 kV and above generating stations, high voltage direct current terminals, and inter-regional and inter-national tie lines and both ends of 400 kV and above lines at the state and ISTS level. Also, PDCs would be installed at SLDCs, RLDCs, the National Transmission Asset Management Centre and the NLDC. The analytics software of WAMS technology would be developed by IIT Bombay. Phase I was awarded to Alstom in January 2014 and costs Rs 3.57 billion. Similarly, Phase II would cover the installation of 554 PMUs at various substations and development of 11,530 km of optical ground wire network along with the installation of 215 units of auxiliary power supply equipment at substations and power plants. Surveys for PMU locations and control centres for PDCs have already been completed and prototypes of some functionalities such as vulnerability analysis of relay and dynamic/linear state estimator of the analytics software have already been developed.
With better monitoring and control systems in place, the URTDSM project would facilitate the integration of a large quantity of intermittent and variable renewable power into the grid. The deployment of PMUs across the country is the first such large-scale undertaking anywhere in the world. This project is likely to enable India to set the standards for smart technology in the transmission sector.