A Planning-oriented Contingency Analysis Tool for Custom Power System Models Beyond Native Capabilities of Widely Adopted Power System Software

Siemens PSS/E, PowerWorld, and DIgSILENT PowerFactory) when integrating custom models that are not natively supported. The CAT specifically addresses the challenge of incorporating emerging technologies like the Modular Static Synchronous Series Compensator

(M-SSSC) into grid planning and security assessments. Modern power systems face compounding stresses from aging infrastructure and rapid and increasing renewable energy integration. Contingency analysis assessing grid behavior following unexpected events (e.g., transmission line outages) is critical for maintaining secure operations. However, standard software packages rely on rigid data structures and lack flexibility to incorporate custom model elements without extensive modifications. This creates delays in leveraging advanced and emerging technologies for comprehensive system analysis.

The developed tool, built based on Siemens PSS/E, bridges this gap by enabling contingency analysis with user-defined models. It uses Python and the PSS/E API to execute load flows, apply contingencies, and monitor violations while incorporating custom models. The CAT is designed to accept four input files: project file (.sav/.raw), contingency file (.con), monitoring file (.mon), and subsystem file (sub). A user-friendly interface allows file upload and automated analysis execution. The M-SSSC is a FACTS device that controls power flow by injecting a voltage in quadrature with line current, modifying effective line reactance. The tool models a

M-SSSC device, which operates in four modes: Monitoring (the device is bypassed), Fixed

Reactance, Fixed Voltage, and Automatic Current Control Mode. In steady-state modeling, the device can be simply represented as a series reactor or capacitor. The developed CAT was validated using the ISO-NE network comprising 18,500 buses, supported by Vermont Electric Power Company (VELCO). VELCO faces challenges managing power flows due to excessive tap changes on their Phase Shift Transformer (PST) at Sandbar substation, caused by fluctuating power flows from increasing New York wind generation. MSSSCs are being integrated to reduce mechanical tap transitions and extend PST lifespan.

Comparative testing against PSS/E's built-in contingency analysis showed that while the native tool completes analysis in approximately 3 minutes, the developed tool requires about 15 minutes total (including file loading, element retrieval, and contingency simulation). Critically, adding the M-SSSC under consideration custom model increased computation time by only 12 seconds, demonstrating minimal computational overhead. The CAT successfully identifies overloaded elements, voltage violations, and provides actionable insights for grid reinforcement planning. Also, the tool provides significant advantages by enabling contingency analysis with non-native, user-defined models.

By enabling contingency analysis with non-native models such as the M-SSC, the CAT directly supports strategic investment decisions in the context of the energy transition. Operators can evaluate, prior to capital commitment, whether emerging FACTS technologies provide sufficient congestion relief under realistic N-1 and N-2 scenarios and the corresponding economic added value.

Future development will focus on supporting additional custom models, expanding monitoring capabilities, adding more simulation parameters, and generating richer output formats for comprehensive analysis. This approach empowers grid operators to evaluate scenarios previously unfeasible with traditional tools, supporting more resilient power system planning.