Phasor Estimation in the Presence of DC Offset and CT Saturation

Abstract

A hybrid algorithm for phasor estimation is proposed that is immune to dc offset and current transformer (CT) saturation problems. The algorithm utilizes partial sum (PS)-based and multistage least-squares (MLS)-based methods before and after CT saturation is detected, respectively. The MLS-based method is initiated when the third difference of the secondary current detects the start point of the first saturation period. The determination of each saturation period is based on the sum of the secondary current from the start point of the first saturation period. A least-squares (LS) technique estimates the dc offset parameters from the single-cycle difference of the secondary current in the unsaturated periods. Removal of dc offset from the secondary current yields the sinusoidal waveform portion. Finally, the LS technique is used once again to estimate the phasor from the sinusoidal waveform portion. The performance of the algorithm was evaluated for a-g faults on a 345-kV 100-km overhead transmission line. The Electromagnetic Transient Program was used to generate fault current signals for different fault angles and remanent fluxes. The performance evaluation shows that the proposed algorithm accurately estimates the phasor of a current signal regardless of dc offset and CT saturation. The paper concludes by describing the hardware implementation of the algorithm on a prototype unit based on a digital signal processor.

An Accurate CT Saturation Classification Using a Deep Learning Approach Based on Unsupervised Feature Extraction and Supervised Fine-Tuning Strategy

“…Comparison results reveal that AI methods perform better than conventional harmonic schemes. Furthermore, conventional protection schemes [11][12][13][14][15] use various signal processing techniques to extract the meaningful features. Due to manual feature selection, we sometimes capture unimportant or useless features, which increases the model complexity.…”

Phasor Estimation Algorithm Based on the Least Square Technique during CT Saturation

“…After the first saturation is completed, the phasor can be estimated using any method suggested in [5]- [7]. Until then, the phasor is given by ( ) …”

“…The suggested algorithm in [6] only uses a least mean square fitting method without a saturation detection technique. A hybrid phasor estimation method in [7] utilizes partial sum-based and least square-based methods before and after CT saturation. This method can deal with the effect of DC offset and CT saturation.…”

New approach for power transformer protection based on intelligent hybrid systems

“…Concerning the application of GA for the estimation of the parameters represented in (1), it should be mentioned that a complete model of the voltage and current signals was considered in [13,15] in order to estimate the fundamental component, including the estimation of the harmonic components, as well as the decaying DC offset. It is well known that the decaying DC offset represented in (1) results in a phasor estimation error, depending on the algorithm used [16]. It must be pointed out that the GA presented a very good performance considering traditional methods such as the Discrete Fourier Transform (DFT) technique.…”