Teams of engineers are working 24x7 to prevent further breakdown of transmission lines of the northern grid though such breakdowns cannot be ruled out completely, say transmission officials. "It is an extraordinary situation. In my 37 years in the power sector, I have not seen anything like this,' RP Singh, chairman and managing director of Power Grid Corporation of India, the country's largest transmission utility, said two days after one of the most serious grid disturbances hit North India. About 50 transmission links tripped in the 21,000-Mw northern grid on Friday, affecting supply in Delhi, Haryana and Uttar Pradesh. This has been blamed on "climate change' resulting in scanty winter rains, which clean transmission links. High humidity at night reacted with "unprecedented' dust and pollutants in insulators to cause a breakdown. "The insulators are totally blackened due to vehicular pollution and brick kilns. It is a man-made problem,' said Singh. Though all links are restored as of now, officials are not sure what night fog and humidity will bring. The immediate plan of action is to undertake manual "detergent cleaning' of insulators on an urgent basis next week. At a meeting held late Saturday, stretches requiring immediate cleaning were identified. "The long-term solution has to be new insulators. For that, the Central Electricity Authority will evolve a consensus among the affected states,' said Singh. The bill is likely to be more than Rs 150 crore, say officials. "It is a natural calamity,' said a senior official at the Central Electricity Regulatory Commission. The transmission lines are designed to work smoothly with some level of dust and pollution but the levels reached "unprecedented' levels. The partial grid disturbance was prevented from escalating into a grid collapse, which would have taken days to restore. "There is no problem with our transmission system. It is just that more frequent cleaning is required,' said a senior official of a transmission company. According to transmission sector officials, long-term measures for controlling line disturbances include shifting of such kilns away from the transmission lines.