Phasor Estimation of Transient Electrical Signals Composed of Harmonics and Interharmonics

Jon Vazquez,Miguel Angel Zorrozua,Jose Felix Miñambres,Jorge Lázaro

doi:10.3390/en14165166

Abstract

Numerical relays have become essential tools for carrying out the protection and surveillance tasks of electrical power systems. These relays implement their functions from the phasors of the electrical network signals, estimated by digital processing using digital filters. Digital filters must meet certain requirements, such as providing a fast and effective response to increasingly complex transient signals made up of components that make the estimation process difficult. In addition to the decreasing exponential (decaying dc offset), harmonics, and signal noise, it must be added that the interharmonic components that in recent years have acquired great relevance, mainly because of the increase in non-linear loads and the extensive use of power electronic systems. The presence of these interharmonic components causes a poor response in most of the filters implemented today. This article presents the design of a new digital filter, C-CharmDF (Cleaned Characteristic Harmonic Digital Filter) for phasor estimation on noisy transient signals with decreasing exponential components, harmonics, and interharmonics. A detailed study was carried out for severe transient situations and stationary signals. It was found that the method can be suitable for relays that implement both fault location functions and system protection functions.

Highlights

Today, the existing protection and surveillance schemes of an EPS (Electrical Power System) use digital numerical relays
In addition to the decreasing exponential, harmonics, and signal noise, it must be added that the interharmonic components that in recent years have acquired great relevance, mainly because of the increase in non-linear loads and the extensive use of power electronic systems
This article presents the design of a new digital filter, C-CharmDF (Cleaned Characteristic Harmonic Digital Filter) for phasor estimation on noisy transient signals with decreasing exponential components, harmonics, and interharmonics

Summary

Introduction

The existing protection and surveillance schemes of an EPS (Electrical Power System) use digital numerical relays. These relays implement their functions on the basis of an internal calculation process with network electrical signal phasors, which are properly processed and digitized (ADC, anti-aliasing filter, etc.). The mathematical operations and techniques used in digital processing for phasor estimation are implemented by a DSP (Digital Signal Processor), which uses specific logical-mathematical algorithms commonly called digital filters. The DFT is a good phasor estimator when the wave is composed of harmonics and continuous components of constant values. It has precision problems when the input signal contains terms of another nature. It is important to point out that it is precisely under fault conditions when it is more important and necessary that the functions implemented in the relay receive reliable information about the state of the system

Methods

Results

Conclusion