For the given circuit shown in figure, D1 is forward bias mode - On state D2 is in reverse bias mode - off state D3 is in reverse bias mode - off state.
Voltage sag: It is usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors. Voltage sag is the short reduction in the RMS voltage between 0.1 to 0.9 pu for a duration of 0.5 cycle to 1 minute
The methods often employed in practice to improve system stability are: 1. Increasing System Voltage 2. Reduction in Transfer Reactance 3. Using High Speed Circuit Breaker 4. Automatic Reclosing 5. Transient Stability 6. Turbine Fast Valving 7. Application of Braking Resistors 8. Single Pole Switching:
Tank - Name of power station - capacity 1 - Vindhyachal Thermal Power Station - 4,760MW. 2 - Mundra Thermal Power Station - 4620 MW 3 - The Sasan Ultra Mega power plant - 3960 MW 4 - The Tiroda thermal power plant - 3300 MW