Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
PHILOSOPH OF ISLANDING • Inter-Connected operation of Modern Power Systems has increased vulnerability of widespread propagation of any disturbance. • It is therefore essential to frame a reliable defense plan • Faulty portion of the system should be quickly isolated or “Islanded” to save the rest of the system • Designing of successful islanding schemes requires consideration of an enormous number of contingencies. • Load-Generation balance by UFR load shedding is to be done prior to islanding Philosophy of Relay Actuated shedding • Manual Response time often too large; low frequency actuated relays are thus essential • Shedding to be done in stages and quantum of shedding may be decided assuming loss of generation from the largest unit in operation • Severity of Disturbance can sometimes be assessed from the rate of frequency decline and relays capable of sensing df/dt prove highly useful in such cases • Sufficient quantum of load should be shed at a frequency much higher than the islanding frequency • Proper calibration of UFRs to be ensured to the extent possible • Loads identified for the specific islands should not be touched during normal UFR shedding Philosophy of Islanding • Islanding of a sub-system and in particular, a power station, should be resorted as the last alternative to save the system. • Load to be included in an island should preferably be radial and neither fluctuating nor unbalanced in nature • At least one machine in each island to be kept in free governor operation and automatic combustion control. • For selective islanding, sensing of reverse power and building of logic alongwith frequency, may be a correct criteria • Relays on priority loads like coal and traction should have a setting of 1 to 1.5 HZ lower than the islanding frequency • All efforts to be made to maintain reactive power balance in the island since demand would be fluctuating in most cases, leading to unstable operation of the generators • Generator capability limits are considerably modified when operated at a voltage and a frequency significantly different from the nominal • To ensure adequate reactive absorption capability, special attention needs to be paid on G.T. tap position and setting of AVR. POSSIBLE SYSTEM PROLEMS UNIT FAILURE TRANSFORMER/ LINE FAILURE REDUCED NETWORK REDUNDANCY LOSS OF GENERATION BUS ISOLATED LINE OVERLOAD OR UNSATISFACTORY BUS VOLTAGE INSUFFICIENT GENERATION LOSS OF LOAD SYSTEM COLLAPS E ISLANDING