Transient Stability Analysis

The recovery of a power system subjected to a severe large disturbance is of interest to system planners and operators. Typically the system must be designed and operated in such a way that a specified number of credible contingencies do not result in failure of quality and continuity of power supply to the loads. This calls for accurate calculation of the system dynamic behavior, which includes the electro-mechanical dynamic characteristics of the rotating machines, generator controls, static var compensators, loads, protective systems and other controls. Transient stability analysis can be used for dynamic analysis over time periods from few seconds to few minutes depending on the time constants of the dynamic phenomenon modeled. Transient Stability Analysis is the PowerApps simulation module dedicated to simulating electromechanical transients in three phase electric power systems. It features an extensive library of equipment and controller models, the capability to include user-defined controls, a very flexible user-interface and powerful graphics. Transient Stability Analysis module utilizes the simultaneous implicit trapezoidal integration solution technique for network, machine and controller equations. The program supports the capability to test the step response of controllers and User Defined Modeling for system equipment and controllers.

General Features of Transient Stability Analysis

• Transient models of excitation systems, turbine governors, static-var compensators, power system stabilizers and HVDC controllers.
• Load shedding / islanded operation.
• Transient stability analysis of multiple-islanded systems with solution for each of the islands.
• Choice of generator models. From simple classical generators with constant voltage behind transient reactance to modelling detailed synchronous machines with variable voltages behind sub-transient reactances.
• Standard IEEE excitation system models and turbine and governor models.
• Commercial excitation models and governor models.
• Models for power system stabilizers and different stabilizing signals.
• Modelling load characteristics similar to that in the load flow analysis.
• Modelling load characteristics as function of frequency.
• Dynamic models of Induction motor and its load.
• Motor starting studies. Motor modelling by their equivalent circuits or by the measured response during starting along with mathematical model for load torque as function of speed.
• Under frequency/Under Voltage relay operation simulation.
• Load shedding.
• Islanded operation.
• Element opening/closing.
• Loss of generators.
• Multiple transient stability disturbance scenarios for each base case load flow study. Note that, multiple load flow case studies can be performed followed by multiple transient stability simulations for each load flow study case.
• Plots of selected bus frequencies and bus voltages. Note bus frequencies are different from generator frequencies.

Reports and Recommendations from Transient Stability Studies

1. Plots of Dynamic response of Generator rotor angles, frequencies, power outputs, voltages, excitation system outputs, governor-prime mover outputs
2. Plots of Line Flows, transformer flows, bus voltages, bus frequencies
3. Plots of Motor dynamic variables where required
4. Plots of the system variables that are of interest from protection point of view [example frequencies, distances seen from distance relays, fault currents seen from overcurrent relays etc]
5. Recommendation related to protection and control, operating strategy, Control settings of equipments [for example power system stabilizer, relay settings, load shedding schmes etc], based on various study cases considered

Transient Stability Comparison between PowerApps and ETAP

Single Pole Open/Close Simulation Validation Document