Rotor_Angle_Stability_4.pdf

1Power System Analysis and Dynamics Topic: Rotor Angle Stability Dr C.Y. Chung Tel:Email: eecychun@polyu.edu.hk Room CF613, EE Department, HKPolyU (Reference Books: (1) “Power System Stability and Control” by Prabha Kundur, McGraw Hill Inc., 1993 ) 2 Classification of Rotor Angle Stability Steady-state stability (small-signal stability) ? Very small disturbance (very gradual change in load) ? Not involved the dynamics of rotating machines such as synchronous machine ? Study by the P-δ curve Dynamic stability (small-signal stability) ? Small disturbance (load change) ? Involved the dynamics of rotating machine including AVR etc. ? Neglects system nonlinearities (assume system to be linear) ? Study by eigenvalue technique Transient stability ? Large disturbance (loss of load or generator, short-circuit, line outage, etc.) ? Include system nonlinearities ? Study by Transient plot 3 Control of a Generator Vref excitationsystem potential transformer power system stabilizer turbine governor system O U T P U T voltage Vt reactive power Q active power Pe frequency f rotor speed Ω Epss fspec Efd Pm ? + + ? 4 Calculation of real and reactive power transmission For receiving end: Similarly, for the sending end: I jX Er∠0°Es∠δ rSsS*IEjQPS rrrr =+= ? ? ? ? ? ? ? ? ? += ? ? ? ? ? ? ?+ = X EEEj X EE jX EjEEE rrssr rss r 2 * cos sin sincos δ δ δδ X EEEQ P X EEP rrs r rs r 2 max cos sinsin ? = == δ δδ X EEEQ P X EEP rss s rs s δ δδ cos sinsin 2 max ? = == Pr and Ps are equal because it is a lossless system. Maximum power transfer is at angle δ equal to 90° (Steady-state rotor angle stability) 5Steady-state stability analysis: power angle curve A load line representing constant sending end mechanical power. The stable intersection of the mechanical power and the electrical power-angle curve is on the left at an angle less than 90°. The right side intersection is unstable: A small increase in mechanical power at the sending-end generator acc