1. NORTHERN REGIONAL GRID SYSTEM CONTINGECY AND RESTORATION

2. NORTHERN RGIONAL GRID : TYPICAL CONDITIONS Typical location of the generating stations vis-à-vis load -- pit head thermal generating stations in the south-east part, -- most of the hydro stations in the north-west part and -- load concentration in the central part of the grid, thereby -- requiring to wheel large quantum of power for long distances Region having largest number of constituents -- 9 number of states/U.T and 3 numbers of C.S. Gen. agencies -- Number of hydro projects having joint ownership -- Criss-crossing of transmission network owned by different agencies Wide variation in the regional load profile -- load crash of the order of 5000MW due to sudden change in weather -- steep fall in demand at certain instances, particularly during winter nights Special requirements by some states -- by J&K due to strategic location and weather conditions -- by Delhi due to being capital and strategic nature of load

4. SYSTEM CONTIGENCIES IN NORTHERN GRID Load generation imbalance. -- Low Frequency -- High Frequency Voltage related contingencies --Low Voltage --High Voltage Failure of transmission network System hunting

5. SYSTEM CONTINGENCIES : LOW FREQUENCY Sudden/gradual loss of generation --Failure of station’s auxiliary power supply --Critical fault in a sub-station area --Sudden interruption of gas supply in a GT plant --Station’s auxiliaries tripping due to voltage collapse --Tripping of evacuating circuits from a station Sudden/gradual increase in load Tripping of inter-regional links Environmental effects --Choking of filters --Wet coal conditions --Sudden inrush/depletion of water

6. SYSTEM CONTINGENCIES : HIGH FREQUENCY Sudden/gradual loss of load due to change in weather conditions Excessive generation due to PLF linked incentive/reward schemes Excessive generation due to deficient commercial mechanism Loss of load due to tripping of circuits/ICT’s Tripping of inter-regional links

7. SYSTEM CONTINGENCIES : LOW VOLTAGE Inadequate VAR compensation at user’s end Utilities drawing large VARS from the grid Overloaded transmission/distribution network Inadequate VAR generation by some generators Deficient planning/design of sub-stations Deficient commercial mechanism

8. SYSTEM CONTINGENCIES : HIGH VOLTAGE Unloading of the circuits due to sudden crash in demand Reluctance by generators to operate in leading mode Improper switching of Reactors/Capacitor banks Deficient planning/design of sub-stations Deficient commercial mechanism

9. SYSTEM CONTINGENCIES : FAILURE OF TRANSMISSION NETWORK Failure of Rihand-Dadri HVDC poles Failure of circuits in 400KV AC network in east-west corridor Incomplete 400KV ring aroud Delhi System Simultaneous tripping of large numbers of EHV circuits in certain parts of the grid due to foggy and inclement weather coniditions Failure of transmission circuits in J&K system

12. SYSTEM CONTINGENCIES Total blackout in northern grid during last few (6)years: --20 th December 1996 --2 nd January 2001 Other partial disturbances: --Disturbances due to failure of equipment --Disturbances due to voltage collapse --Disturbances due to critically low frequency