Storm a perfect recipe for blackout, but supply restored in record time: Discom

Written by Geeta Gupta | Geeta Gupta | New Delhi | Updated: Jun 4 2014, 18:17pm hrs
DelhiThe storm last Friday claimed 14 lives in Delhi.
The devastating storm that claimed 14 lives in the national capital last Friday was a perfect recipe for a blackout in Delhi and the entire northern region, according to Praveer Sinha, chief executive officer and executive director of Tata Power Delhi Distribution Limited (TPDDL).

The northern electricity grid had tripped because of underdrawal as several connecting towers and at least 68 transmission lines collapsed because of the raging winds, which exceeded 75 kmph in some areas.

Before the storm hit, the total load in Delhi was 5,200 MW. During the storm, the load fell within a few minutes at the rate 200 MW per minute. According to officials, this was a perfect case of northern grid failure, but the system survived because of combined efforts of Northern Regional Load Dispatch Centre, transmission, distribution and generation companies.

The severity of the storm on the power network could be gauged from the fact that it resulted in the tripping of 68 transmission lines in the northern grid. The load loss was at the rate of 200 MW per minute, resulting in a northern grid load loss of about 8,000 MW, including 4,000 MW in Delhi alone. TPDDL also lost 1,050 MW during the storm, Sinha told Newsline.

The crisis was managed because of an effective disaster management system, contingency planning, inter-grid connectivity, backfeeding and running the network on emergency mode, which restored the power supply in TPDDLs area in record time of 36 hours, Sinha said. India has five electricity grids northern, eastern, northeastern, southern and western run by the Power Grid Corporation, which operates more than 95,000 circuit km of transmission lines. All the grids are inter-connected; except the southern grid.

In 2012, the northern grid had collapsed due to low frequency on July 30. Another failure four days later had led to a cascading effect and the collapse of three more grids, plunging as many as 21 states into darkness.

The storm last Friday came from the Hisar-Sonepat side and first hit the north and northwest parts of the city before before spreading across NCR, says a release by TPDDL. Sinha said that over 1,000 trees fell on the power lines across north Delhi alone. The storm damaged Delhi Transcos five towers on the 400/220 KV Bawana-Rohini line, and two towers from DTLs 400/220 KV Mandola-Gopalpur line.

The TPDDL network suffered majorly because around 500 fully grown Eucalyptus trees fell and that damaged nearly 250 low tension and high tension electricity poles in its network spread across 510 sq km. These Eucalyptus trees are a big hazard and when they fall on the power lines, they completely snap power supply, Sinha said.

A stock taking by the discom revealed broken conductor lines at several locations, hundreds of broken LT/HT ABC at different locations, several damaged distribution transformers and broken guard wires, which hold the poles in place at various locations.

At present, the total transmission restoration from Delhi Transco is only 50 per cent because of the damage to towers. The power supply situation, however, has been normalised due to immediate activation of the discoms disaster management plan and quick interconnections between grids and back feeding, and the PGCIL Emergency Restoration System (ERS) for early restoration of affected lines.