Case Studies

The following projects are representative of Powertech’s power system studies and generator testing.

Small-Signal Stability Analysis

In this study, Powertech conducted a small-signal stability analysis of an interconnected power system. Small-signal stability refers to the ability of power systems to withstand small disturbances, which appear as poorly or negatively damped oscillations and cause security violations. This study focused on the sensitivities of the critical system modes with respect to different system conditions, transfer patterns, and contingencies. The results provided recommendations for tuning the existing Power System Stabilizers and adding new stabilizers in the system to accomplish optimal performance for identified critical modes without adverse effects.

Path Rating (Total Transfer Capability) Study

Powertech performed a simultaneous transfer study of a rating increase on a transmission path to determine and address potential adverse impacts on four related paths. The study involved analysis of scenarios for different seasonal load conditions and generation patterns. For each simultaneous transfer scenario, the project team performed post-transient power flow analysis, voltage and transient stability studies in accordance with North American Electric Reliability Corporation/ Western Electricity Coordinating Council (NERC/WECC) planning criteria and applicable system operating orders. Appropriate mitigation measures were also considered. The study demonstrated that, under favorable system conditions, the path rating could be increased with implementation of mitigation measures.

Generator Testing and Model Validation

Generator model validation testing was conducted on eight hydro-electric generating units, according to WECC requirements. Since the previous model validation testing, some of the generators had been rewound and their excitation systems retrofitted with new digital controllers. To comply with the WECC generating unit baseline model validation policy, and to provide the utility with validated model parameters, Powertech performed testing including: open-circuit saturation, excitation removal, manual exciter step, direct-axis, quadrature-axis, AVR step response, reactive current compensation, and partial load rejection. The tests were designed and executed based on unit type and associated controls. Computer simulation models were developed, and the model parameters of the generators, excitation systems, and turbine-governor systems were validated using field test results.