An Accurate Offline Phasor Estimation Technique For Fault Location In Series Compensated Lines

In series compensated transmission lines, current and voltage signals measured by the line protection system include considerable sub-synchronous frequency components (SSFCs) which are not sufficiently damped within a typical fault clearing time of line protection system. This does not allow accurate phasor estimation and thereby phasor-based fault location. This paper presents an accurate algorithm which effectively filters out the unwanted frequency components and noise to perform accurate phasor estimation for fault location in series compensated transmission lines. Phasor estimation of a theoretical signal is first evaluated using the proposed method, Direct-Prony analysis and 4-cycle discrete Fourier transform algorithm. Then, various fault locations of a 500 kV series compensated transmission line simulated in PSCAD/EMTDC are used to comprehensively evaluate the performance of the proposed technique. It is shown that the proposed method can effectively attenuate SSFCs and other unwanted frequency components in current and voltage signals allowing accurate phasor estimation

Fault Location in Series Compensated Transmission Lines

Due to the integration of modern technology such as electric vehicles, the emphasis is expected to shift from mechanical to electric power. Therefore, the need of increasing the power transmission capacity of the electric grid gets highlighted. Since, the construction of transmission lines is a tedious task owing to legalities, environmental impacts and high costs, the series compensated transmission lines are gaining popularity due to lesser costs and faster construction time. The series capacitor compensated transmission lines are very crucial lines due to the greater power being transmitted through them. Therefore, an accurate fault location becomes a prerequisite for limiting the loss of revenue and power continuity. However, fault location in series capacitor compensated transmission lines face multifaceted challenges due to the variety of factors including but not limited to the presence of sub-synchronous frequency components in the measured signals, interdependence of the fault current level and operation of series capacitor protection unit, presence of non-linear element, i.e., metal-oxide varistor as a part of series capacitor protection unit and dependence of the existing fault location algorithms on zero-sequence parameters of the series capacitor compensated transmission line which cannot be estimated accurately. In this thesis, the task of fault location in series capacitor compensated transmission lines has been explored in detail covering the entire spectrum of challenges starting from signal processing to how to obtain the fault location value with the least amount of uncertainty. In this thesis, firstly a phasor estimation technique called the Enhanced Prony-DFT based on analysis in discrete-time domain has been proposed which identifies and completely removes the transients present in the measured signal, thus yielding highly consistent and accurate phasors. Fault location in series compensated transmission line is used as metric for the verification of the accuracy of estimated phasors. Thereafter, the focus is shifted towards the fault location algorithms for series compensated transmission lines. All the studies found in literature have considered the location of series capacitor in the middle of the transmission line. Therefore, secondly the configuration of series compensated line when series capacitor is located at one of its ends is also studied. It is discovered that the well-known fault location algorithms for series compensated transmission lines yield significantly higher errors when the series capacitor is located at the end of a transmission line. Therefore, rendering the already existing fault location algorithms useless for practical applications. Thirdly, the impact of series capacitor protection unit on fault location has been investigated which leads to a significant observation that MOV may get bypassed before the interruption of the fault for numerous fault scenarios. Therefore, a new complimentary fault location technique is proposed which provides more precise and accurate fault location results for the fault scenarios where MOV gets bypassed before fault interruption. The proposed complimentary technique is relatively more immune to the adverse effects of measurement errors and errors in the estimation of zero sequence components as compared to the existing techniques

Wind Generator Transients’ Computation using Prony Method

The impact of wind generation on the electrical system should be assessed to guarantee error free operation and good power quality indicia. In this paper switching transients within wind generation units have been analyzed. Transients were simulated and measured. A Prony model of the signal and a nonlinear regression method were applied to determine transients’ parameters for various operation modes of the wind generator. Both methods delivered quite satisfactory results, but the regression method was sensitive to local minima

Decaying DC offset current mitigation in phasor estimation applications: A Review

Decaying DC (DDC) offset current mitigation is a vital challenge in phasor current estimation since it causes malfunctioning/maloperation of measurements and protection systems. Due to the inductive nature of electric power systems, the current during fault inception cannot change immediately and it contains a transient oscillation. The oscillatory component acts similar to an exponential DC signal and its characteristics depend on the X/R ratio of the system, fault location, and fault impedance. DDC attenuates accurate phasor estimation, which is pivotal in protection systems. Therefore, the DDC must be eliminated from the fault current (FC) signal. This paper presents an overview of DDC mitigation methods by considering different groups—before the discrete Fourier transform (pre-DFT), after the discrete Fourier transform (post-DFT), the least square-based (LS-based), and other methods. Through a comprehensive review of the existing schemes, the effects of noise, harmonics, multiple DDCs (MDDCs), and off-nominal frequency (ONF) on the accuracy of DDC estimation, were recognized. A detailed discussion (along with some simulation results) are presented to address the main advantages/disadvantages of the past studies. Finally, this paper presents a few suggestions for future researchers, for researchers to investigate more implementable solutions in this field

Nonlinear regression applied for power quality disturbances characterization in grids with wind generators

The impact of wind generation on the electrical system should be assessed to figure out potential hazards to system operation and deterioration of power quality indices. In this paper signal processing algorithms has been applied to analyse switching transients within wind generation units. Nonlinear regression method and Prony model were applied to determine transients’ parameters for various operation modes of the wind generator. Both methods delivered quite satisfactory results, but the regression method was prone to local minima

Methodology for characterizing electric power system response and locating the energized capacitor banks using conventional power quality data

textA relatively small harmonic current with frequencies near or at the power system parallel resonant frequencies could excite the power system into a resonance condition. While a capacitor bank is not the root cause of the condition, it facilitates and helps cause the problem. This is because when the capacitor bank is energized, the system resonant frequency could shift closer to existing harmonic frequencies produced by nonlinear loads. Therefore, the objective of this dissertation is to quantify the power system characteristics corresponding to the parallel resonant frequencies and system damping. Additionally, since a capacitor bank actively facilitates the resonance condition, the relative or exact location of the involved bank must be determined. This dissertation first presents a practical and accurate methodology to estimate system parallel resonant frequencies by performing spectral analysis of the voltage and current transient data immediately after the capacitor bank switching. The proposed method is also robust in that the accuracy of the resulting estimates is not affected by prevalent harmonics in the system. This dissertation provides two efficient algorithms for estimating the system damping parameters using the Hilbert and analytic wavelet transforms. These algorithms take advantage of the principle of an asymptotic or weaklymodulated signal, for which the signal phase varies much more rapidly than the amplitude. The zero-input voltage response or free response of the capacitor bank energizing can be categorized into these asymptotic signals, and one can assign a unique time-varying amplitude with the system damping information and phase pair by building analytic signals. System model reduction theory also allows us to interpret or quantify this damping as an effective X/R ratio. This dissertation defines two fundamental signatures of shunt capacitor bank energizing. It demonstrates that these two signatures can be utilized to accurately determine the relative location of an energized capacitor bank whether it is upstream or downstream from the monitoring location. This dissertation also presents an efficient and accurate methodology for finding the exact location of an energized capacitor bank. Once a PQ monitor is found to be upstream from the capacitor bank by the relative location finding algorithm, the proposed algorithm can further determine the exact location of the switched capacitor bank by estimating the distance between the PQ monitor and the energized capacitor bank. Thus, one can pinpoint the energized capacitor bank causing the resonance.Electrical and Computer Engineerin