LONDON The precise cause of widespread power failures that cut electricity supply on Tuesday to states where half of India's 1.2 billion people live will take many months to establish, and may never be known for certain.
So any analysis at present must be speculative.
The most likely explanation is a small localised problem that rippled across the network as grid managers lost control of power flows and automatic relays shut down transmission lines and power plants to prevent further damage to equipment.
India needs more power generation and transmission capacity but that will not solve the problem on its own. Even more urgently, India needs investment in grid control technology, a smarter grid, and a thorough review of operational procedures to reduce the likelihood that massive power failures will recur.
LOSS OF CONTROL
Cascading power failures are not uncommon in transmission systems under stress. In 2003, cascading failures knocked out power to more than 50 million people across the north-eastern United States and parts of Canada, some for as long as four days.
On the afternoon of August 14, 2003, a local problem in the Cleveland-Akron area of Ohio that had been rumbling all afternoon spread like a tidal wave across the network, shutting down 508 generating units at 265 separate power plants in less than five minutes, including emergency stoppages at 10 nuclear stations.
As automatic relays shut down the most overloaded transmission lines and vulnerable power generators, electricity surged around the rest of the network taking increasingly unpredictable pathways, unbalancing more and more parts of the system, and forcing further emergency shutdowns, until the grid and power generation collapsed across the entire region.
Something similar appears to have occurred in northern India on July 30, shutting down power supply to nine states including Delhi on the country's northern grid region. (here)
It was followed by an even more widespread collapse the next day, that included not just the northern grid but also the eastern and north-eastern power grids, extending power failures to 18 states and two territories covering half the population. The country's other two grids (western and southern) appear to have been unaffected.
On July 30, a disturbance occurred on the northern grid at 2.35 a.m., according to Power Grid Corporation of India, which manages the network. Power was restored by using hydro-generation and sourcing electricity from the neighbouring western and eastern systems to help restart thermal generators across the northern area, according to the grid controller.
On July 31, however, another disturbance hit the three northern, eastern and north-eastern regional networks at 1.00 p.m. Power Grid Corporation responded by routing power up from the unaffected western and southern grids, as well as maximising hydroelectric generation across the northern region.
The simple response is to blame a growing imbalance between supply and demand. The country's aging power system is struggling to cope with underinvestment and booming demand, including widespread theft and non-payment problems, as well as extensive subsidies and artificially low tariffs. India's rapidly growing economy is bumping up against the limits imposed by an underdeveloped power generation and transmission system.
But such analysis is simplistic. Even severe imbalances between supply and demand should not cause widespread grid collapse.
Properly engineered and run networks have multiple mechanisms for managing supply/demand imbalances, including: extra generation from frequency and spinning reserves which can be called up at short notice; demand management; voltage reduction; and ultimately forced load shedding, where power is cut to certain users and areas to protect supplies to the rest of the network.
In a system under stress, however, even tiny problems can escalate to knock out power to tens of millions or even hundreds of millions of users.
In the case of the August 2003 blackout, an extensive investigation by the U.S. and Canadian governments traced the failure back to something as apparently trivial as tree growth and hot summer weather, which caused a handful of small local transmission lines to overload after sagging in the heat and becoming entangled in branches.
It escalated into a crisis because of computer system failures and poor communications and operating practices among grid controllers. There wasn't even an overall imbalance in power supply and demand. There was plenty of power, just not the right sort in the right places ("Final Report on the August 14 2003 Blackout" April 2004).
In India, the original cause of the power failure is not yet known (and may never be known because such investigations are exceptionally complex). Whether a transmission line failed, a generator went offline unexpectedly, a sudden uptick in demand exceeded supply, or someone somewhere in the grid control system made a mistake, or some combination, is not yet known.
But both the August 2003 and August 2012 blackouts are signs of power systems operating under stress. In the 2003 incident, the joint U.S.-Canadian task force issued 46 separate recommendations, mostly focused on improved grid control. India's problems are more complex and will be more expensive to resolve.
Soaring power demand has eroded the margin of spare reserves in the generation system, leaving grid controllers with less and less room for error. Limited transmission capacity within the five regional grids as well as between them reduces system flexibility further in the face of local problems.
There may also have been some element of human error, computer failure or weaknesses in operating protocols, though that will only become known after a lengthy enquiry by the grid company and the government.
Simply adding a few more power plants to boost nationwide generation capacity would not in itself avoid the kind of cascading failures reported this week. After all, the United States and Canada suffered a similar crisis even though there was no overall shortage of power generation in the region at the time.
No power system can ever be 100 percent robust. Power systems are the biggest machines ever built by mankind, and their interconnectedness means there is always some risk that a problem with one tiny part will bring widespread collapse.
Problems are not limited to developing countries. In North America, there have been eight comparable grid failures since 1965, affecting between 2 million and 50 million people each time, according to a listing presented in the task force's Final Report.
The North American task force identified a number of common factors in most of these eight outages, including "(1) conductor contact with trees; (2) overestimation of dynamic reactive output of system generators; (3) inability of system operators or coordinators to visualize events on the entire system; (4) failure to ensure that system operation was within safe limits; (5) lack of coordination on system protection; (6) ineffective communication; (7) lack of 'safety nets'; and (8) inadequate training of operating personnel."
What India needs is a comprehensive upgrade of its power system. Upgrades will involve some combination of more generation capacity, more transmission lines (the often unloved part of the system), and better grid control, as well as new pricing and billing systems to ensure customers pay the full marginal cost of their supply and reduce theft and wasteful use.
Part of that is a smarter power grid. The smart grid concept is most often associated with the United States, where it has been heavily promoted by the Obama administration, and specifically smart metering designed to manage peak-time power consumption by encouraging more load-shifting and use of off-peak power by households and small businesses.
But the biggest gains are likely to be in developing countries, using technology to upgrade grid management and control. Smart grid technology can report unusual fluctuations at any point across the grid in a matter of seconds. Linked with better control systems, it can initiate procedures to protect the grid and prevent widespread power failures, isolating problems in a sub-region, rather than letting them spread across the network like wildfire. (Editing by Anthony Barker)