A combination of factors, including a skewed load generation balance across the regional grids, rampant grid indiscipline by northern states, depleted reliability margins on account of system outages and the failure of all major grid protection mechanisms, resulted in the cascade grid collapse witnessed on two successive days in end-July. Immediately after the incident, Central Electricity Regulatory Commission (CERC), through a petition on August 1, 2012, directed POSOCO (Power System Operation Corp Ltd), the arm of PGCIL that manages the country’s national power grid, to investigate into the incidences of grid failure on July 30 and 31 and submit a report within a week. This preliminary report, distinct from the detailed expert committee report that is currently underway, is based on information received from the sites and has been submitted to CERC on August 9. Excerpts: UNDERLYING CAUSES Skewed load generation balance across the grids The load generation scenario in the synchronous Northeast-East-West-North (NEW) grid was highly skewed in the month of July. There was a spurt in agricultural demand in the northern region on account of the failure of the South West monsoons, resulting in a large gap between the demand and supply situation in the north. On the other hand, there was a surplus condition in the western region due to high generation availability, resulting in heavy underdrawal by western region states. This unscheduled interchange resulted in heavy power flow towards the northern region from the western and eastern region. The large quantum of power flow in real-time was opposite to the power flow envisaged in planning time horizon. Grid indiscipline The regulations allow deviations from the schedule as long as the operating parameters are within the prescribed standards. Yet the problem of grid indiscipline continued to be a large concern. The underdrawal/overinjection by the western region constituents and the overdrawal by the northern region states continued despite several appeals and directions to restrict the deviations from schedule by the utilities. This grid indiscipline was a major cause for both the grid disturbances. Depleted reliability margins On July 30, the 400 kV Bina-Gwalior-Agra II line was under planned-shutdown, while the 400 kV Zerda-Kankroli line was taken under emergency shutdown. On July 31 too, the 400 kV Binda-Gwalior-Agra II line was under planned shutdown, and subsequently two more lines (the 400 kV Zerda-Kankroli and Zerda-Bhinmal line) went under forced outage. This resulted in significant reduction in reliability margins. Impediments to speedy restoration of systems Restoration was taken up post the grid disturbance as per the procedures. However, difficulties were experienced on account of constraints in extension of start-up supply, difficulties in black start, load generation-imbalance, reactive energy imbalance, failure of built up subsystems/islands, deficiencies in communication, inadequate telemetry and inadequate reactive resources. The report has called for renewed emphasis on mock trial of the contingency plans.