Development and Testing of a New Modified Discrete Fourier Transform-based Algorithm for the Protection of Synchronous Generator

A novel full-cycle modified discrete Fourier transform-based digital protection scheme for generators is presented in this article. A laboratory setup has been developed to cater various abnormal and faulty situations applicable to a scaled generator. It includes utility supply, motor-generator set, synchronizing panel, current transformers/potential transformers (CTs/PTs), digital storage oscilloscope, and 3-phase variable load. A control circuit has also been developed comprised of a proposed algorithm, auxiliary relay, and circuit breaker (contactors). The proposed scheme depends on phasor values of modal voltage (V-mod) and current (I-mod) derived by the algorithm in MATLAB (R) software. The outcome of the proposed modified discrete Fourier transform-based protection scheme is compared with the numerical relay (available in the laboratory), which has an inbuilt fast Fourier transform/discrete Fourier transform (FFT/DFT)-based algorithm. Various conditions, such as overload, over/under voltage, over/under frequency, ground fault, reverse power, and loss of excitation, have been simulated in the laboratory for the validation of the proposed scheme. Due to finer characterization of the fundamental signal derived by the proposed algorithm compared to numerical relay, it successfully detects and sends a trip signal for all types of abnormal/faulty conditions. The experimental results confirm the satisfactory operation of the proposed algorithm in the developed laboratory prototype.