Swift restoration of the lines and simultaneous load reduction by the system operator prevented a cascade tripping that could have caused a flashover and endangered the grid.
Officials said the tripping was largely attributed to the lack of early winter rain. A combination of dirty insulators, atmospheric dust and carbon, along with the dense winter fog forced multiple tripping of lines that could have caused blackouts or brownouts in large parts of the grid.
This phenomenon, which was earlier largely confined to areas in the vicinity of Delhi due to the atmospheric pollution around the capital, has now spread to the northern hinterland, especially Uttar Pradesh, Punjab and Haryana.
This is mostly due to excessive crop burning in Punjab and Uttar Pradesh, leading to carbon in the air adding to the vehicular and industrial pollution. Under dense foggy atmospheric conditions, break down strength of the surface of the porcelain insulator reduces due to the deposit of pollutants over it, triggering an outage.
The most recent incident of this kind took place on January 2, 2010, causing a partial blackout in the northern regional grid, affecting Punjab, Haryana, J&K and Himachal Pradesh. This was triggered by tripping of multiple lines due to transient faults caused under dense fog conditions in the affected areas.
Similar incidents of multiple lines tripping, resulting in partial blackouts in major sections of the northern region, have taken place on March 7 and 9, 2008; January 27 2007; February 16 2006; December 23, 2002; and January 2, 2001.
In a bid to mitigate the impact of fog on the safety of the electricity grid, grid managers have begun monitoring weather parameters and have installed temperature and humidity transducers at key substations in the northern region. Such monitoring was found to be very useful in handling contingencies arising due to fog related tripping in real time.
Early winter rains have been very helpful in washing away some of the pollutants from insulators and power lines before the onset of fog. In addition to monitoring weather conditions during winter nights, preventive action such as replacement of porcelain insulators by anti-fog or polymer insulators having better breakdown strength under such conditions, are being taken, officials said.