Effects of Sampled-Values Data Quality on Responses of Time-Frequency Based Digital Relays

Time-frequency based digital protective relays can offer several advantages of high accuracy, improved reliability, and fast response over other protective relays. These protective relays employ half-band digital finite impulse response (FIR) filters to process currents and/or voltages to extract fault signatures, which facilitate accurate detection and identification of fault events. Coefficients of the employed half-band digital FIR filters are determined by wavelet or phaselet functions. The signal processing part in a time-frequency based digital protective relay processes samples of measured currents and/or voltages. As a result, attention has to be paid to the measurement, digitization, and communication of current and voltage data. Power systems utilize the IEC 61850 standard to implement data communication between measurement, control, and protection devices. This article assesses the impacts of the IEC 61850 sampled values on the accuracy and response speed of time-frequency based digital protective relays. The presented assessment is conducted for two sample cases; the transformer differential protection and arcing current fault detection and identification. Test results show that the accuracy and response speed of time-frequency based digital protective relays are maintained, when measured currents and voltages are communicated using the IEC 61850 sampled values.