Application of block pulse functions for digital protection of power transformers

The author describes an application of block pulse functions for digital protection of power transformers. Digital relay algorithms are developed to extract fundamental and second-harmonic components. These components are then used for harmonic restraint differential protection of transformers. In comparison with the algorithms based on the Walsh and Haar functions, the proposed method is computationally simple and can be used with any sampling frequency. It is concluded that offline testing of the method with simulated inrush and internal fault current data clearly indicate that the method can provide fast and reliable trip decision. The method is suitable for microprocessor-based protective relays.>