According to reports, blackouts across northern India this week have highlighted the urgent need to improve grid control by investing in more modern technology for measuring and visualising power flows across the network to ensure corrective actions can be taken more quickly.
India lags behind grid operators in advanced economies, as well as emerging markets such as China, Russia, Brazil and South Africa, in rolling out a new generation of technology based on the global positioning system (GPS).
This technology conveys a better understanding of how the grid behaves under normal conditions, and cuts the crucial reaction time in the event of an abnormal disturbance from minutes to seconds, reducing the risk of catastrophic failure.
In a bitter irony, before this week’s collapse, Power Grid Corporation of India had already begun to take the first steps towards the creation of a smarter power grid, installing a new generation of monitoring devices at nine points on the country’s northern grid, in a pilot programme that has yielded “a huge leap” compared with data from the old system.
Ultimately, the corporation has proposed installing 1,669 new monitoring devices, with the first 1,186 units and supporting communication equipment rolled out by 2014-15, according to a report issued earlier this year (“Unified Real Time Dynamic State Measurement” February 2012).
But India is far behind China, which had 300 new measurement devices on its electrical network by 2006, and now has more than 1,000 in place. By the end of this year, China will have new monitoring units at all substations operating at 500,000 volts or more, and at all power plants with a capacity of over 300 megawatts.
South Africa, Brazil and Russia are among other countries which have deployed or plan to roll out a large number of advanced monitoring units.
Better grid control is needed because electrical networks are becoming larger. The trend towards super-grids is worldwide as countries try to make better use of generation capacity, as well as integrating more renewable and intermittent sources of power generation onto the grid and reducing reliance on predictable but polluting fossil fuels.
India has already linked up and synchronised four of its five regional grids (covering the northern, eastern, north-eastern and western parts of the country) with a combined capacity of around 137 gigawatts (GW). The remaining southern grid (49 GW) is expected to be synchronised with the others by 2014.
Increasing grid size has made monitoring and control much more complicated, as significant amounts of power are exchanged between regions, heightening the risk of congestion at times along certain transmission corridors. Seasonal weather patterns, weather effects, and faults can all lead to big shifts in power flows.
In the longer term, the challenge is likely to get even harder, as the power network tries to integrate more renewable energy from variable sources like wind and solar onto the grid.
Like other grids, India relies on a Supervisory Control and Data Acquisition/Energy Management System (SCADA/EMS) to tell controllers what is going on.
Data on power quality (voltage, current and frequency) gathered from generating plants and sub-stations is passed up through a four-level hierarchy of group, state, regional and national control centres, using a combination of fibre-optic, microwave and voice communication networks.
The SCADA/EMS measures power quality every 4-10 seconds. But it can take as much as 30 seconds for data to be received by the national control centre owing to delays in the system. In effect, grid controllers are able to view a snapshot of the system about once a minute.
Given the August 2003 blackout in North America knocked out 508 generating units at 265 separate power plants in less than five minutes, the existing system is much too slow. Crucial seconds are lost before the control room is even aware there is a problem, let alone able to pinpoint the origin of the disturbance.
Moreover, the quality of the data provided by SCADA/EMS is poor. Because measurements from generating plants and sub-stations reach the control centre with different time delays, it is difficult to line them up properly to provide a consistent grid-wide picture at a given instant. So controllers have only a fuzzy idea of exactly how the various parts of the network are performing at any given moment.
Even weeks or months after the event, it can be difficult to reconstruct the precise origin of a massive power failure such as the blackouts on July 30 and July 31, as analysts struggle to work out which parts of the system failed first, making it hard to learn lessons or detect vulnerabilities.
The new generation of wide area monitoring systems (WAMS) use phasor monitoring units (PMUs) dispersed across the network at strategic locations to take measurements at super high speed. They sample a wider range of aspects of power quality (including magnitude and phase angle as well as frequency, current and voltage) as many as 25 times per second.
PMU measurements are time-stamped so measurements taken at different locations across the grid can be lined up (synchronised) accurately to provide a comprehensive view of the entire grid at a central location. PMUs are all linked up to the GPS so each applies a time-stamp to every observation using the same common reference time.
Coupled with faster communications technology to transmit the data back to the central and regional control rooms, synchrophasor technology enables grid managers to “visualise” the entire grid in real time, updating in milliseconds, rather than minutes.
The benefits of synchrophasor technology, such as India has been testing, are threefold, according to Power Grid Corporation’s report.
In the first stage, the corporation hopes it could provide a faster, more comprehensive view of how the network is operating in real time. Historical data could be analysed to learn more about how the grid performs under normal operating conditions, what the safe operating limits are, and to trace the source of faults.
In the second stage, the data archive could be analysed to make suggestions to grid operators about how to keep the grid stable and reliable.
In the third and final stage, synchrophasor technology and sophisticated computer analysis might be able to do all of the above without human intervention (the so-called “self-healing grid”).
The idea of a self-healing grid is still a long way from reality anywhere, let alone in India. But improved measurements and understanding of how the grid operates would still represent a huge step forward.
Power Grid Corporation has installed PMUs and GPS at nine substations on the northern grid (including Agra, Kanpur, Hisar, and the giant new Karcham Wangtoo hydroelectric project). “Even the limited exposure with synchrophasor data has been a revelation” according to the report’s authors.
Rolling out the full network of more than 1,600 PMUs, with associated communications infrastructure and data aggregation systems, would be expensive. It will take time to analyse the enormous amount of data to improve situational awareness and develop new protocols for improved grid management (let alone try to build a system that can suggest responses in real-time).
But it is probably the best chance to avoid more widespread blackouts.