Govt. Exams
Entrance Exams
Flux reduces drastically when field is short-circuited. As back EMF reduces, armature current increases causing motor speed to increase dangerously.
Total line impedance = 150 × 0.4 = 60 Ω. Zone 2 reach = 80% × 60 = 48 Ω
IS 1885 and IEEE standards recommend a minimum coordination time interval of 0.5 seconds between protective device operations to ensure selectivity.
During voltage sag, STATCOM operates as a voltage source injecting capacitive reactive power (leading current) to support and restore the system voltage.
The stability of a multi-machine system depends on relative rotor angles between machines. Loss of synchronism occurs when relative rotor angle exceeds critical limits.
KE = H × S where S = rated MVA. KE = 6 × 50 = 300 MJ. (H is defined as H = KE/MVA)
As per CEA guidelines and recent Grid Code specifications, LFC keeps the system frequency within ±0.2 Hz of 50 Hz nominal frequency to ensure quality power supply.
Pre-insertion resistors and reactors limit the inrush current and transient overvoltages when capacitor banks are switched, ensuring smooth energization.
Indian Grid Code 2023 requires differential protection as primary with distance protection as backup for critical transmission lines to ensure faster fault clearance.
Subtransient reactance X''d represents the initial response of the generator to a sudden disturbance and is used for calculating the first few cycles of fault current.
