Govt. Exams
Entrance Exams
Maximum power transfer (Pmax = V²/X) occurs when power angle δ = 90°, regardless of absolute voltage magnitudes.
Fault level = MVA base / (Zth in p.u.), where Zth is the equivalent impedance of the entire network.
δcr is the limiting rotor angle; if exceeded during a fault, the machine cannot return to synchronism even after fault clearance.
H is the inertia constant (M/2×SB) representing the kinetic energy relative to the system base power.
Indian Grid Code 2023 specifies that when reactive power reserves fall below 15% of the available reactive power limit, emergency corrective measures must be initiated to prevent voltage collapse.
The transient stability limit is always greater than the steady-state stability limit. A system can maintain transient stability even after a disturbance that would violate steady-state stability.
Loss of synchronism occurs when the generator rotor continuously accelerates because decelerating torque never becomes greater than accelerating torque, preventing the rotor from returning to synchronous speed.
QC = (V²/Xc) where Xc = 1/(ωC), Total C = 0.008 × 200 = 1.6 µF, Qc = (132000)² × 2π × 50 × 1.6×10^-6 = 256.7 MVAR
IEEE 1588-2019 specifies ±0.01 Hz accuracy for steady-state frequency measurement in PMUs used for power system monitoring.
The swing equation 2H(d²δ/dt²) = Pm - Pe - D(dδ/dt) describes rotor angle dynamics, where H is inertia constant, Pm is mechanical power, Pe is electrical power, and D is damping coefficient.
