Commonwealth 245 West Michigan Avenue,
Jackson, MI 49201

Seminole Electric Cooperative

On an annual basis, Seminole must compare the capability of the breakers owned by Seminole or its members to the fault currents in the system to demonstrate that the breakers are operating within their interrupting ratings. Seminole runs this test via a Python program.

Seminole Electric Cooperative was in search of engineering services to support updating and running the Python program on selected buses “on demand” via a dialog and selected Commonwealth Associates, Inc. for the job.

Seminole provided Commonwealth with the existing Python program, PSS/e raw and seq input files, an example of the existing text file output, and an Excel (CSV) output specification. Using the existing Python code as an example, Commonwealth redeveloped Python code to produce the specified CSV output.

The standard governing breaker rating calculations, C37.010 – 1999 (R2005), call for calculating X/R ratios precisely and applying DC and AC decrement curves. The standard states that these ratios are not to be used for breaker duty calculations. PSS/E fault analysis has options for calculating the ANSI X/R ratio and these decrements. These X/R ratios, provided we can define contact parting times and proximity to synchronous generation, can be included in the report in addition to the Thevenin X/R values.

At the end of the project, Commonwealth will send its Project Engineer to Seminole’s office for a day of training on installation and use of the program. The objective is for Seminole personnel to be able to use, maintain, and improve the delivered product.

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