On 30 and 31 July 2012, two large-scale power blackouts occurred in India, which can easily be termed as the worst power crisis ever in the history of mankind. The first of the two outages affected nearly 350 million people, while the second one involved a whooping 670 million people, one-tenth of the world’s population and spread over 21 out of 28 Indian states.
As the global media turned its attention towards the issue, key players in the Indian power sector were at loggerheads over a blame game.
However, the important question that needs answering is what really happened which caused the outage and how can it be avoided in future. Seeking answers to this question lies in understanding the electricity supply chain in India.
Backbone of Indian Electricity: The Electricity Grid
The electrical network in India is divided into five regional grids: northern, north-eastern, eastern, western and southern regional grid, as shown in Figure 1.
Around two-thirds of the electricity generated in India comes from coal-fired thermal power plants, which are concentrated in the Eastern region owing to their proximity to major coal mines. Hydro generation, which accounts for another one-tenth of generation, is located mostly in the Northern and North-Eastern regions. On the other hand, the major power draining loads are located in the North, West and South regions.
To fuel India’s growing economy, this geographically skewed generation-consumption profile necessitates a heavy traffic of power flows across thousands of miles. The arteries for these cross-country flows are a network of 400 kV transmission lines and the upcoming 765 kV lines. The distribution of power within these regional grids is in turn, managed independently in each state of India by its power utility.
During the first wave of electricity reforms in India in early nineties, the plan for connecting the regional grids to form a National Grid was conceptualized, following which all regional grids, except the Southern region achieved interconnectivity. The synchronous operation of these regional grids, forming the combined grid called North-East-West (NEW) Grid, is an attempt at easing the power exchanges among these geographic regions to manage the generation excess and deficits. A power transmission ‘superhighway’ was commissioned at that time to tightly link these regions together. This corridor which is made up of high capacity lines connecting Agra and Gwalior in the west to Sasaram in Bihar in the east, aimed primarily at allowing voluminous flow of power from thermal power stations in the east to the load centres in west and north.
For the coordination of power exchanges between these regions, a National Load Dispatch Centre (NLDC) was formed in Delhi to manage the inter-regional exchanges, in addition to the existing Regional Load Dispatch Centres (RLDCs) which managed the intra-regional power balance so far. These Load Dispatch Centres (LDCs) are autonomous subsidiaries of the public sector Transmission System Operator (TSO) called Power Grid Corporation of India. Their priority is to ensure generation-load balance throughout the network.
Indian electricity grid is expected to operate always at a frequency of 50 Hertz, which is essential for efficient operation of household appliances, industrial loads and for increased lifetime of infrastructure.
Whenever the demand in a regional grid exceeds the supply, the frequency of the grid tends to drop. To compensate this effect, the generators in the region and all over the interconnected system start pumping in more power into the network which then requires more power to be transmitted over the transmission lines. Carrying power above the rated capacity of the transmission lines results in increased thermal stresses in them and when the safety limits are crossed, leads to activation of protective shutdown of the lines. This partial shutdown of some of the grid connectors, in turn, may lead to increasing stress and subsequent shutdown of the other lines in the network, followed by turning off of generators and eventually causing a blackout.
The sequence of events during the outage days of July 2012 closely resembles this classic ‘spiral breakdown effect’ of a power system.
What Caused the Outages?
Around 0230 hours on 30 July 2012, there was a disturbance in the NEW grid leading to the disconnection of the Northern Regional Grid from the rest and ultimately resulting in an outage plunging 8 out of 28 Indian states into darkness. Mere 32 hours later, around 1300 hours on 31 July 2012, a similar disturbance emerged again, this time paving way to the collapse of Northern, North-Eastern and Eastern Grid, together affecting about 670 million people. This outage is the largest outage ever in the history of electric networks. To investigate the cause behind these grid failures, understanding the conditions prevailing in the network prior to the disturbance is of prime importance.
As evident from the reports(this, this) published by the enquiry committee on blackouts commissioned by the regulatory authority of India, Central Electricity Regulatory Commission (CERC), the NEW grid was operating in a stressed situation throughout the month of July. The failure of South-West monsoon rains had led to an unprecedented increase of agricultural demand in Northern region. This was accompanied by a power surplus in the Western region which resulted in very high outflows of power to the Northern region. Adding further to the woes of the imbalanced system, only two of the four 400 kV high capacity West-North interconnections were operational as shown in Figure 2.
One of the two unavailable lines was placed under planned outage since the 28 July for up-gradation to 765 kV and the other underwent a forced outage the next day due to equipment failure. This was a crucial development, as reported here, towards exerting enormous pressure on the two available lines, one of which (Agra Gwalior 400 kV line) was already carrying power at the edge of its capacity limits of around 1000 MW. On 29 July, the critical Agra-Gwalior line had nearly collapsed at around 1500 hours, 36 hours prior to the actual major grid breakdown. Even then no stringent steps were taken at this stage to curb the demand in the northern region or to curtail the generation in the western region and the situation prevailed. Instead power from the surplus western region detoured via the states of central and eastern India to reach the deficit northern region. This is where the decisions of state government-owned utilities came into play.
On their power lines, the states are expected to operate a special class of protective devices called- Under Frequency Relays (UFRs) which respond to changes in frequency, thus detecting sharp drops in frequency (indicative of high loading in the system) and disconnecting the loads connected to them.
However, the state-owned utilities seldom maintain these relays and are often under tremendous political pressure to continue drawing power from the grid even if the system appears to be compromised. The non-tripping of these UFRs put the system in a state of high risk such that the failure of any single crucial component would have led to a cascade of shutdowns. And this is exactly what happened.
The timeline in Figure 3 portrays the sequence of events that began at 0010 hours on 30 July with the further weakening of West-North linkage leading to the isolation of the Northern region from the NEW Grid and ultimately the blackout.
Just 32 hours after this first outage, there was another disturbance in the NEW grid, originating again in the critical West-North regional interface.
The existing conditions of high power vortex in the northern region and power surplus in the western region still held true. As a part of the supply restoration process, three out of the four NR-WR 400 kV links were made operational. When two of these failed to operate in overloaded condition at 1300 hours on 31 July, a very similar cascade of shutdowns of other NR-WR links followed as shown in Figure 4. However, in this case the grid was already considerably weakened by the outage on the previous day. Several WR-ER connecting lines were still down and the entire system was in a compromised state, struggling to barely meet the load. At this stage, 38 links between the various parts of northern, western and eastern grids were disconnected due to overloading within a short span of one minute. Along with this, most of the generation protection systems in the eastern region shut down, thus taking away a huge chunk from the net generation pool. The Northern, Eastern and North-Eastern regions were cut-off from the Western grid and consequently, suffered a blackout. Meanwhile in the Western region, which had a surplus of generation and had lost its loads in the Northern region, the frequency overshot to 51.4 Hertz. However, the immediate isolation of the Western region from the NEW grid and tripping of generations saved the region from suffering an outage.
Restoration of SupplyOn both days, the process of restoring supply to the loads was initiated soon after the incident. However, due to the sheer magnitude of the incident, it took a long time for the grid to come back online because the generators needed to be put on-line in several stages, always such that the supply corresponds to the loads already connected at each stage. The restoration of supply on both days was extended to a large portion of the loads lost within 8–10 hours of the outage. However, loads in some areas were still un-served for as long as 16–20 hours after the actual grid collapse. In addition to the size of the impact area of the outage, the generation mix constituted another key issue for delay in the restoration process. Due to the delay in onset of monsoons, the hydro power generation in Northern region was negligible and the loads mostly relied on the thermal power generated from coal-plants in the east. It is quite widely known that thermal power stations aren’t the fastest responding power stations around and incidents of tripping such as this require the plants to be cooled down and stabilized prior to ramping up production again. This process can take as long as 6–8 hours for a typical thermal power station.The critical loads of railway traction power were among the first ones to be restored. The New Delhi Airport, one of the busiest airports in the world, had power supply within 15 seconds of the outage, thanks to its own backup provisions. All major hospitals in the region were also equipped with their own backup system which came online soon after the grid collapse(reported here). The fact that power outages are not infrequent, even in cities, provides a huge economic drive for medium-sized to large-sized commercial loads to own a backup supply system, diesel generators in most cases. All industrial setups have their own Captive Power Plants (CPPs) which in this case, led to minimizing the impact of the outage on large scale production processes.
Could It Have Been Avoided?
The outages were clearly a spiral down effect of several factors that led to increased stress on the network, which ultimately gave away. A few of the most obvious situations that led to these outages are listed below.
- Heavy Over-Drawl by the Northern States and Over-Supply by the Western States. Despite several directives from the National Load Dispatch Centre in Delhi, the northern states continued over-drawing power from the grid in the order of 2000 MW, while the western states overproduction was around 2700 MW. This would have been alright to maintain, had the NR-WR links been in place. The planned outage of a crucial 400 kV artery for up-gradation to 765 kV and the forced outages of few links led to the inability to mitigate this supply-demand skew. The state utilities, when in need of power, otherwise have the option of buying it from private producers. However, since this requires upfront payment and the state utilities, usually with red in their balance sheets owing to the political pressure of keeping retail tariffs low, had more incentives to resort to the cheaper way of overdrawing power from the national grid.
- Self-Interest Ahead of Grid Security. The operation of Under Frequency Relays (UFRs) to curtail part of the load on the system could have minimized the impact of the outage or perhaps could have avoided it completely. However, the socio-political pressure and the huge negative balances of the state utilities renders them with no leverage required to take steps towards mitigating their concerns on grid safety. As a result of this continued non-compliance to load curtailment measures by several states at the same time, the disturbance in the system took form of a large-scale blackout.
- Economics of Generators. To cope with the issues of unexpected regional grid imbalances, the mechanism of Availability Based Tariffs (ABTs) has been put in place since 2002. ABT is a tariff scheme for electricity suppliers, which provides them with incentives to stick to their committed scheduled generation plan. According to this scheme, generators and loads (which could be industries or state utilities) declare the power they are likely to supply to the network or draw from it, 24 hours in advance to enable the Load Dispatch Centres to plan the physical flows in the network day ahead. However, if the loads consume more than their committed schedule, the demand exceeds the supply in the system and hence frequency starts to drop. As a result of this, the cost of each unit of power escalates, making it more expensive for loads to buy power and more profitable for generators to supply more than agreed. If a buyer at such a time reduces its consumption, he is rewarded by being paid a special premium, called the Unscheduled Interchange (UI) Rate, thereby incentivizing the loads to do so. The same UI Rate is charged as a penalty to generators who fail to deliver the promised power in such a scenario. The UI Rate is fixed by the central electricity regulator, CERC and increases with increase in deviation of frequency from the 50 Hertz. However, with time rising fuel costs have led to increase in the cost of electricity generation making the per unit generation cost considerably higher than the UI rate. Thus in a situation of heavy demand, power producers would rather make the economic choice of paying the penalty at UI rate rather than produce more power, contrary to what the UI mechanism expected them to do. When a large number of generators start doing this, the supply-demand gap worsens, paving way to blackouts such as these.
- Improper Grid Management and Inadequate Monitoring of the Network. The visibility and situational awareness of the load dispatch centres (LDCs) was severely compromised during the time leading up to the outage and while restoration. This unavailability of real-time data from the network made it very hard for LDCs to issue operational directives to the states while keeping the health of the entire grid in mind.
Stricter adherence to grid discipline, maintaining the system security as the highest priority, modernization of system diagnostic equipment and increased coordination among the state utilities and LDCs are surely the foremost steps towards ensuring that similar situations don’t emerge again.
It was also observed that the UI mechanism, originally targeted at improving grid security, in fact led to the other opposite extreme. More and more market players have started abusing the UIs rather than being involved in long-term or short-term supply contracts, which have the advantage of making the process of forecasting and identifying transmission constraints in the network much easier as compared to UIs. The need is to seriously review the UI mechanism and take steps to restrict the use of such unscheduled transfers only to the situations of actual grid compromise.
During this two-day mishap, several small- and medium-sized pockets of loads and generators survived by successfully alienating themselves from the grid in time. Many of these were areas with a high renewable penetration and with micro-grids which catered to the demand of a few thousand users. Considering this, the question arises if India would be better off investing more in decentralized renewable generation, thereby also achieving goals of carbon-free electricity, in the near future? And the future looks optimistic. In India, since early 2013, for the first time the cost of generating solar power a (8.78 Indian Rupees per unit of energy) has become less than that by diesel generators (17 Indian Rupees per unit of energy)(here, here and here). This has happened partly due to the reduction in solar panel prices driven by Chinese manufacturers and due to the increasing crude oil price. Even in the short term, this could prove to be a major incentive for owners of the diesel backup systems to switch to roof-mounted solar panels. The cost of storage using batteries to employ solar energy during night is the limiting factor for the replacement of fossil generation in micro-grids and small-scale generation. Nonetheless, the flexible operation of micro-grids undoubtedly has the possibility to curtail demand at crucial peak hours and prevent such large-scale outages in future.
Chronic shortage of fuel and an ever increasing demand has led to the severe burdening of Indian power sector. In the year 2011–12, India suffered a national energy deficit of 8.5 per cent and a generation-load capacity deficit of 10.6 per cent during peak hours, as reported by Central Energy Agency (CEA), India here. The impact of these deficits falls heavily on the rural areas where supply is restricted to 8–12 hours a day in most states. During the same year, the big cities of urban India had to endure around 60 hours of outage per month during the season of peak demand (here).
Hence it is strange that this outage, as unparalleled as it may appear, seemed like an almost normal event to most people in the country, who are used to suffering frequent supply disruptions even in the cities. While a billion dreams of development are envisioned by its populace, the machinery and governance mechanisms to fulfil them are hardly in place in India.
(Originally published in Energy Science Bulletin, Volume 3, Issue 2. A triennial Bulletin on energy edited and published by Energy Studies Institute, National University of Singapore)