1. 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

2. 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

3. 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.

4. POSSIBLE SYSTEM PROLEMS
UNIT
FAILURE
INSUFFICIENT
GENERATION
TRANSFORMER/
LINE FAILURE
LOSS OF
LOAD
REDUCED
NETWORK
REDUNDANCY
LINE OVERLOAD OR
UNSATISFACTORY
BUS VOLTAGE
BUS ISOLATED
ISLANDING
SYSTEM COLLAPSE
BACK