A Cost-Effective Transformer Protection Scheme Through Microcontroller-Based Design Utilizing DFT Phasor Estimation

This paper represents the design and implementation of a microcontroller-based complete transformer protection unit, utilizing a new DFT-based (Discrete Fourier Transform) current phasor estimation algorithm that offers a more suitable and cost-effective alternative to DSP-based systems for contemporary power systems. The conventional microcontroller-based numerical relay has limitations regarding malfunctions caused by decaying DC signals, magnetizing inrush current, over-excitation inrush current, and CT saturation. Since the developed microcontroller-based relay incorporates functions to eliminate these malfunctions, it has been tested and shown to be more reliable and sensitive to faults. The proposed single-unit relay is designed to provide comprehensive protection for power transformers, safeguarding against external faults such as overcurrent/earth faults, and internal faults through differential protection. Additionally, it monitors various transformer parameters including oil and winding temperature alarm and trip signals, gas levels, sudden pressure changes, and oil level, eliminating the need for multiple relays. The system is especially appropriate for small-scale power systems because of its simple implementation and cost-effective design. Testing on a commercially available relay test bench confirms the system's effectiveness in detecting and protecting the transformer from fault conditions.