Precise Amplitude and Phase Determination Using Resampling Algorithms for Calibrating Sampled Value Instruments

Abstract

Sampling-based calibration systems for calibrating “Sampled Value” (SV)-based instruments for substation automation require synchronised and time-aligned sampling processes. As the signal frequency of the power grid is always asynchronous to the standardised sampling frequencies according to IEC 61869-9, the sampled waveforms of the calibration system and of the SV-based device under test can be resampled to be synchronised and to allow better accuracy in the following measurements based on the Discrete Fourier Transform (DFT) of the resampled waveforms. The paper presents simulations and results for different resampling algorithms. A modified sinc interpolation method with a finite impulse response (FIR) is presented. The deviation of the results for the root mean square (RMS) and phase angle is in the order of 10−8V/V (or rad) for normalised frequencies of up to 20% of the sampling frequency. No practical degradation in the presence of noise and harmonics could be observed. In addition, laboratory experiments demonstrate the realization of the proposed resampling process in the future SV-based calibration systems for SV-based instrumentation.

Traceable calibration system for non-conventional current sensors with analogue or digital output

“…After the transfer of the data (SVs), the channel for the synchronisation (SynChnnel) is selected and the frequency of the signal is determined. The resampling processing [14] can be chosen when the detected signal frequency is not synchronised to the given sampling parameters. The FFT spectrum analysis is supposed to determine rms values and phase angles of the voltages and currents of the SV in the frequency domain.…”