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Types of stability and factors affecting transient

Short answer

Steady state stability handles small gradual load changes with no controls, limit EV/X at 90 degrees. Dynamic stability covers small disturbances with AVR, governor, PSS over seconds to minutes. Transient stability deals with large sudden faults in the first swing via the swing equation and equal area criterion. Key factors: loading, fault type/location/clearing time, post-fault reactance, inertia, excitation, reclosing.

Discuss the difference between the transient stability, steady state stability and dynamic stability in power system. Also, explain the factors affecting transient stability of the system.

Difference between the three types

PointSteady state stabilityDynamic stabilityTransient stability
DisturbanceSmall, gradual load changeSmall disturbanceLarge, sudden (fault, line trip)
Controls consideredNone (constant EE, PmP_m)AVR, governor, PSS includedUsually neglected (first swing)
Time frameContinuousSeveral seconds to minutesAbout 1 s (first swing)
AnalysisLinearised, Ps=dPe/dδ>0P_s = dP_e/d\delta > 0Linearised with controls, eigenvaluesNon-linear swing equation, EAC, step-by-step
LimitEV/XEV/X at δ=90∘\delta = 90^\circCan exceed steady-state limit with fast controlsLower than steady-state limit
ConcernMax power transferDamping of oscillationsLoss of synchronism in first swing

Factors affecting transient stability

FactorEffect on transient stability
Pre-fault loading (PmP_m, δ0\delta_0)Higher loading gives larger δ0\delta_0 and a smaller margin
Type of fault3-phase fault is most severe, then LLG, LL, LG
Location of faultFault near the generator bus reduces PeP_e most (close to zero)
Fault clearing timeLonger clearing increases the accelerating area; critical factor
Post-fault network reactanceHigher reactance after clearing lowers Pmax3P_{max3} and the decelerating area
Inertia constant HHLarger HH slows the rotor swing, giving more time
Generator transient reactance Xd′X_d'Lower reactance raises power transfer
Excitation level and speed of the excitation systemHigher internal emf and fast field forcing raise PmaxP_{max}
Reclosing schemeFast and single-pole reclosing restores transfer capability
Speed of governor/fast valvingQuick reduction of PmP_m reduces acceleration

✓ Answer checked by Claude Sonnet 5.5

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