How to Evaluate the Saturation of Generator Protective Relay Current Transformer using ETAP software

We'll familiarize ourselves with ETAP's Current Transformer Saturation calculation capabilities and walk you through that particular calculation.
By Jesse Hoffman, Engineering Manager at Energy Systems Group

In this technically rich presentation, we can unravel the critical significance of accurately selecting the Current transformer's accuracy class in mitigating the adverse effects of saturation. Traditionally, electromagnetic transient program (EMTP) software has been the go-to solution for evaluating CT saturation and its implications on protective relay behavior. However, ETAP offers an alternative calculation methodology, providing users with a robust toolset for comprehensive saturation analysis.

The Energy Systems Group, LLC is headquartered in Newburgh, Indiana, and maintains a separate headquarters for the federal team in Eagan, Minnesota. Their offices are located throughout the U.S. and help companies achieve their energy efficiency, resiliency, and sustainability goals.

Location: Newburgh, Indiana, United States

Year: 2023

Selection of the current transformer in medium voltage

Challenges

  • Identifying the impact of the current transformer selection and the work condition on the correct work of the protective relay.
  • Modeling appropriate transient systems that are compliant with typical cases from industry and overcurrent protection.
  • Evaluating the electrical calculations in conformity with the national standards and sizing the best equipment solution, thanks to calculations.

Which solutions did they choose?

Selected applications

They chose the ETAP Base Module with ETAP StarZ and Current Transformer Saturation to analyze protective relay behavior in an easy, flexible distribution power system platform.

The ETAP solution guaranteed compatibility with actual standards. 

Why do they use ETAP?

Main Customer Benefits

  • Easy modeling of the electrical grid system and adding accurate electrical data from the field saves time. ETAP took only minutes once CT excitation curves and burden data were in place, versus hours/days of hand-building an ATP or EMTP model.
  • Simplified but sped calculations in comparison to the other transient calculation methods.
  • The vital user benefit is that intuitive evaluation of the calculation's results and clear visualization with warnings eliminates misunderstandings.
  • If the problem exists, suggest how an operator can solve it (e.g., changing the current transformer or changing protection relay settings).

What do they think about ETAP?

Opinions

Changing this using the same CT calculation in ETAP's model is straightforward. This sequence list will show you when each breaker opens, and we can then conclude if we have appropriate coordination on those breakers or if there is a fault. When examining a particular system, we recommend initiating the process using the ETAP calculation method, as it is the quickest and easiest way to determine whether you have a saturation problem with your CT selection.
By Jesse Hoffman, Engineering Manager at Energy Systems Group

In our case, compared to the ETAP demonstration that we just completed, which took a few minutes to determine if there was a problem, you can spend hours, if not days, trying to configure the ATP system to match the EMTP results.
By Jesse Hoffman, Engineering Manager at Energy Systems Group



Videos

Evaluation of generator protective relay current transformer (CT) saturation using ETAP

Explore the complexities of current transformer (CT) saturation's impact on protective relay performance in high fault current scenarios, examining the importance of accurate CT selection and contrasting ETAP's saturation analysis capabilities with traditional methods in a real-world scenario, providing insights to enhance protective relay operation and system reliability.


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