Transformer Switching Studies

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What are Transformer Switching Studies?

Transformer switching studies focus on evaluating the electrical impact when energizing a transformer. Improper timing or configuration during energization can result in high inrush currents, RMS voltage drops, temporary overvoltages (TOV), and resonance effects. These issues can lead to power quality disruptions, insulation damage, surge arrester failure, and potential relay malfunctions.

The study assesses the transient RMS voltage drop, inrush current, and temporary overvoltage during transformer energization under various operational conditions and configurations.

Importance of Transformer Switching Studies

Transformer energization is a routine operation in transmission and distribution systems. Transformer switching studies are essential to:

• Grid Compliance: Ensure the transformer meets local electrical grid standards, particularly concerning voltage drops during energization.

• Impact of Renewables: Address potential issues arising from changes in network topology, especially with the increasing integration of renewable energy sources like offshore wind.

• System Planning & Protection: Help determine the proper sizing of pre-insertion resistors to mitigate voltage dips, enhance protection systems, and prevent maloperation during energization.

How Do We Perform Transformer Switching Studies?

1. Data Collection: Gather system data, including the single line diagram (SLD), transformer datasheets (saturation characteristics, losses), and details of shunt reactors, capacitor banks, generators, lines, loads, and network short-circuit levels.

2. Modeling: Model the system using PSCAD/EMTDC software for accurate simulation of the transformer energization process.

3. Simulation: Develop simulation case studies based on the study scenarios provided by clients, ensuring a thorough analysis of energization events.

4. Reporting: Prepare and submit a detailed technical report outlining the findings and recommendations for improving energization practices.

Applicable Standards for Transformer Switching Studies

• CIGRE Working Group C4.307: Study Guide on Transformer Energization in Power Systems.

• IEC 60071-4: Insulation co-ordination guide, providing computational methods for evaluating temporary overvoltages in electrical networks.