Phasor Estimation Technique Research Articles

A Comparative Analysis of MDSC-based Phasor Estimation Technique for Digital Relays in Power System Protection

A Comparative Analysis of MDSC-based Phasor Estimation Technique for Digital Relays in Power System Protection

Comparative Analysis of Phasor Estimation Techniques for PMU Applications

Phasor Measurement Units (PMU) are valuable sources of data which increase the visibility into several fields of application such as power production, transmission and distribution. With the initial goal of obtaining phasor values at fixed points in the network and syncing it to a standard time frame, the technology has morphed into an all-encompassing unit, which has its uses in the field of protection, control and automation. With the application of these units becoming a standard benchmark, the improvement in the current available units is a huge requirement. This study presents a comprehensive analysis of various techniques that is used for the estimation of phasors.

Performance and comparison of different phasor calculation techniques for the power system monitoring

Day to day to electrical power demand increases very rapidly with linear and non-linear load demands. Especially the nonlinear loads are creating the harmonics in the current and voltage signals. The current and voltage signal values are measured with the phasor measurement unit (PMU) for the proper magnitude and phase angle calculation even in the presence of harmonic components in the signals. The performance of the PMU is depending upon the phasor calculation technique. Different technique/methods are available for the phasor calculation, from the method to method there is difference in the accuracy, phasor computation time and complexity. In this paper various techniques for phasor calculation are presented. For better performance of PMU, more accurate and less computation time for phasor calculation technique is required. But in real time, accuracy and speed both may not satisfied with single technique. Need to find a satisfactory technique, which satisfies the speed of phasor computation and accuracy. In this paper it is proposed that direct phasor estimation technique, which gives the better results in terms of accuracy and time and this method, satisfies the requirements for the dynamic monitoring of power system according to the IEEE std. C37.118.1-2011.

Enhancement of dynamic phasor estimation‐based fault location algorithms for AC transmission lines

A new technique to improve fault location methods in AC transmission lines is introduced in this study. The identification of fault location is carried out using one-end fault location algorithms based on impedance through dynamic phasors. This timely approach relies upon the fact that a fault resistance may introduce errors in the distance estimation when a fault takes place. Therefore, active power variations caused by the fault are used to enhance the fault location algorithms, i.e. power losses increase during the fault period for non-zero fault resistances. The present approach is extensively evaluated, using ATP-EMPT software, which relies upon the computation of a compensation factor associated with the rate of change in the resistance during pre-fault and fault conditions. This is achieved through the estimated phasors for voltage and current. Furthermore, the dynamic phasor estimation technique Taylor-Kalman-Fourier Filter is compared against a static phasor method. The proposed approach is validated using three fault location algorithms which are evaluated under different fault conditions, such as fault inception, location, and fault resistance. Results show that this proposed technique improves the fault location including fault resistances by 3% with respect to existing approaches.

Coupling Capacitor Voltage Transformers Models and Impacts on Electric Power Systems: A Review

Coupling capacitor voltage transformers (CCVTs) are the predominant devices used in high voltage systems to provide scaled-down voltage signals for metering, protection, and control devices. The performances of these devices are subject to errors due to the transient behavior of CCVTs, so that the use of CCVT digital models is essential for studying power systems in order to predict how the equipment dynamics affect protective relaying performances. In this review paper, the authors put together complete information regarding five realistic CCVT digital models available in the literature and perform a detailed sensitivity analysis of their magnitude and angle frequency responses, as well as their influence on phasor estimation, distance protection, and fault location techniques.

Accurate phasor and frequency estimation during power system oscillations using least squares

Accurate estimation of a phasor, frequency, and rate of change of frequency during changing power system condition is important to initiate precise control action for reliable power system operation. Conventional phasor estimation techniques cannot estimate the phasor accurately during dynamic conditions of power system. Furthermore, the phasor-based frequency estimation algorithms are being affected under such conditions. In this study, both angle and amplitude modulation parameters are considered in the signal model to improve the accuracy of the phasor estimation. The method uses Taylor's series expansion to linearise the signal model and computes the signal parameters using least squares. The method first computes the phasor using estimated parameters of the signals, subsequently calculates the frequency and rate of change of frequency. The performance of the proposed method is evaluated for standard test signals. Real signals recorded in numerical relay are used to assess the performance of the proposed method. The results are compared with the available method and found that the method can supplement the existing methods used in phasor measurement units and intelligent electronic devices.

A Novel Distribution-Level Phasor Estimation Algorithm Using Empirical Wavelet Transform

Distribution-level signals are often contaminated with harmonics and noise, along with dynamic conditions like frequency deviations. This paper proposes an empirical wavelet transform (EWT) based M-class distribution-level phasor estimation technique under such polluted and dynamic conditions. The capability of the EWT of extracting different frequency components present in the signal makes it suitable for distribution-level phasor estimation. However, the empirical wavelet filters are designed on the basis of the Fourier spectrum of the signal, which, inturn suffers from a spectral leakage problem at off-nominal frequencies. To avoid the errors arising due to spectral leakage, a sample value adjustment based prefiltering technique is employed. The effectiveness of the proposed estimator is demonstrated on various simulated signals, field-data, and real-time signals obtained from the hardware implementation setup. The proposed algorithm is found to be least affected by the presence of dc components, harmonics, and noise. The use of a fixed window size and fixed sampling frequency makes it suitable for synchronization with GPS clocks. The proposed scheme is also able to provide an accurate harmonic phasor estimation.

Adaptive phasor estimation technique during off-nominal frequency for numerical relays

ABSTRACTThe use of digital multifunction protection relays and their proper integration on the power system and smart grid is an important element. However, the performance of digital relays depends on many factors and needs to be carefully evaluated. These factors may be caused by correct operations with less performance or completely incorrect operations. Frequency deviation is one of those factors which results from unbalanced demand load and generation levels. Load characteristics and generation control response to demand load changes will effect on amount and duration of frequency deviations. Frequency decreases when demand load is higher than generation, whereas it increases when load is less than generation. Protection relays are provided with frequency tracking to reduce the effects of frequency deviations on accuracy of relay decisions. In this paper, traditional frequency tracking technique used on protection relays is modified to give a better performance (less Total Vector Error, TVE) during off-nominal frequency variations. The performance of the proposed algorithm is compared with traditional tracking using Least Square Error (LSQ), and Discrete Fourier transform (DFT) algorithm without any tracking, which are investigated in MATLAB environment.

Phasor Estimation and Modelling Techniques of PMU- A Review

Abstract The values of voltage / current signal at various places in a power network are measured by Phasor Measurement Unit(PMU). The PMU's work on the phasor values of the data collected using Phasor estimation technique. This mechanism is essential for analysis and interpretation of collected data in a correct manner. Therefore, a Phasor estimation process has a lot of importance in design of control mechanism and various protection systems to be implemented. Numbers of PMUs are being installed across the world for different applications such as post fault analysis, state estimation and protection of power system. Since the cost of PMUs is very high, they are placed optimally in the power system such that complete power system is observable. In this study, PMU along with techniques used for phasor measurement has been reviewed. Some of the used phasor estimation techniques viz. zero crossing, DFT and SDFT are described to compute magnitude and phase value of input signal.

Enhanced Phasor Estimation Technique for Fault Location in Series-Compensated Lines

Accurate phasor-based fault location in series capacitor-compensated transmission lines is a challenging task due to the presence of subsynchronous frequency components in the measured voltage and current signals. In this letter, an enhanced technique is proposed based on Prony analysis and discrete Fourier transform to accurately estimate voltage and current phasors for the purpose of offline fault location. A comprehensive simulation and fault-location analysis is performed using PSCAD and Matlab to establish the successful application of the proposed technique to the fault location.

Accurate Dynamic Phasor Estimation Based on the Signal Model Under Off-Nominal Frequency and Oscillations

Accurate and fast estimation of power system phasors is the key to reliable operation of power system and its control/protective equipment. There have been many studies on phasor estimation techniques under dynamic and transient conditions. Although the performance under dynamic conditions of estimators based on the static phasor model has improved, significant errors still exist during large dynamic deviations. Two fast and precise dynamic phasor estimation algorithms under power system oscillations and off-nominal frequency conditions are described in this paper. The methods use the signal model under these dynamic conditions, linearize them by using Taylor’s series expansion, and estimate the phasor using least squares technique. Frequency and its rate of change are also calculated using adjacent phasors with minimum complexity. Results obtained show that the performance errors of the proposed methods are way below the minimum requirement of the standard and better than other similar dynamic phasor algorithms.

A Subspace-Based Dynamic Phasor Estimator for Synchrophasor Application

In this paper, estimation of dynamic phasors, under power-system oscillations, has been proposed using subspace-based techniques. A high sampling rate and few modifications in the subspace-based techniques are suggested to estimate the voltage phasor with a fundamental frequency component without using antialiasing filter to the input signal. The total least squares estimation of signal parameters via rotational invariance techniques and the propagator method are the two subspace-based techniques used for estimating the frequency, as well as the amplitude and the phase, respectively. A compensation for the amplitude and the phase has been proposed to address the dynamic nature of the power-system oscillations. The suggested techniques for the phasor estimation have been tested on simultaneous multiple amplitude and phase oscillations in the presence of noise and also for a fault scenario in New England 39-bus system. The hardware requirement of the proposed phasor estimation technique has also been discussed for its practical viability.

Strengths and limitations of a new phasor estimation technique to reduce CCVT impact in distance protection

This paper evaluates the performance of a new least squares approach that improves the accuracy and speed of convergence of the voltage phasors estimated during CCVT transient conditions. A justification of the validity of the linear mathematical model for the CCVT used is provided together with a short study about the risk of transient ferroresonance. Also, a discussion is presented about operating times of numerical distance relays and the importance of the new phasor estimation considered. The methodology followed to achieve a realistic evaluation in a variety of scenarios is presented. The results show the improvements achievable in most conditions, but also highlight an example scenario where the new method has limitations.

Phasor estimation technique to reduce the impact of coupling capacitor voltage transformer transients

A new least squares technique to reduce the impact of the transient response of coupling capacitor voltage transformers (CCVTs) on the performance of distance relays is described. Several factors that affect the frequency and time responses of CCVTs are considered. The effect of the transient response on the phasor-estimates is illustrated. An improved least squares technique, which uses the knowledge of the frequency of the CCVT transients while estimating the phasors, is presented. A case, taken from a set of studies, is included to demonstrate the performance of the proposed approach. The robustness of the method is verified by a CCVT parameter sensitivity study.