JOIN USPanel fails to identify reasons for grid crash
A government-appointed committee of experts has failed to establish the exact reasons for the failure of transmission grids that led to massive power outage for two consecutive days in the last week of July.
The panel, set up by the Ministry of Power, has concluded that power transmission was disrupted on July 30 and 31 following failure of northern, eastern and north-eastern grids due to a “combination of factors.”
“No single factor was responsible for the grid disturbances on both occasions,” the committee, headed by Central Electricity Authority chairperson Arvinder Singh Bakshi, said in its report submitted to the power ministry recently.
The panel has identified over-drawal of power by “some of the northern region” utilities as one of the factors responsible for the grid failure. This contributed to high loading on 400kV Bina-Gwalior-Agra link.
Since the inter-regional interface was very weak, tripping of 400 kV Bina-Gwalior line on zone-3 protection of distance relay caused the northern region system to separate from that of western region. “This happened due to load encroachment, that is, high loading of the line resulting in high line current and low bus voltage,” the panel said.
There was “inadequate response” by state load dispatching centres (SLDCs) to the instructions of regional load dispatching centres (RLDCs) for reducing over-drawal by the northern region utilities and under-drawal or excess generation by the western region utilities, it added.
The system was weakened by multiple outages of transmission lines in the western- region interface. “Effectively, 400 kV Bina-Gwalior-Agra (one circuit), was the only main AC circuit available between WR-NR (western region-northern region) interface prior to the grid disturbance,” the panel observed.
On July 31, apart from these reasons, the system was weakened by outages of transmission lines in the eastern region network near the eastern-western region interface.
“On this day also, effectively 400 kV Bina-Gwalior-Agra (one circuit), was the only main circuit available. Although, the real power flow in this line was relatively lower than on July 30, the reactive power flow in the line was higher, resulting in lower voltage at Bina end,” the report said.
On both the occasions, correct operation of defence mechanism which include under-frequency relay and rate of change of frequency relay and proper response of governors of generators assisted by the compliance of the instructions of regional load dispatch centres, would have further assured secure and safe operation of the grid, it added.