| A stand-alone prototype digital protective relay for power transformer protection has been designed, implemented and tested successfully. It integrates up to three different relaying functions in a single relay. The data acquisition board consists of seven identical circuits each having a scaling circuit, a sixth-order Chebyshev anti-aliasing filter and a sample-and-hold circuit. All seven signals are then multiplexed and connected to an A/D converter. The digital processing board consists of a TMS320E15 digital signal processor.;The prototype digital relay was tested extensively three months. The relay always cleared all the faults that were applied on the transformer and the relay never maloperated. (Abstract shortened by UMI.);The relay software program is developed for the complete three-phase percentage differential relay with second harmonic restraint for inrush and fifth harmonic restraint for overexcitation. Primary and secondary ground fault protection is also provided. The software is written in modular form such that any relay algorithm can be used by simply changing only one subroutine. The present relay design utilizes the Discrete Fourier Transform (DFT) to extract the current harmonics. |
