Chi-Shan Yu

A New PMU-Based Fault Location Algorithm for Series Compensated Lines

This work presents a new fault location algorithm based on phasor measurement units (PMUs) for series compensated lines. Traditionally, the voltage drop of a series device is computed by the device model in the fault locator of series compensated lines, but by using this approach errors are induced by the inaccuracy of the series device model or the uncertainty operation mode of the series device. The proposed algorithm does not utilize the series device model or knowledge of the operation mode of the series device to compute the voltage drop during the fault period. Instead, the proposed algorithm uses the two-step algorithm, prelocation step and correction step, to calculate the voltage drop and fault location. The proposed technique can be easily applied to any series FACTS compensated line. EMTP generated data using a 300 km, 345 kV transmission line has been used to test the accuracy of the proposed algorithm. The tested cases include various fault types, fault locations, fault resistances, fault inception angles, etc. The study also considers the effect of various operation modes of the compensated device during the fault period. Simulation results indicate that the proposed algorithm can achieve up to 99.95% accuracy for most tested cases.

Transmission network fault location observability with minimal PMU placement

This paper presents a concept of fault-location observability and a new fault-location scheme for transmission networks based on synchronized phasor measurement units (PMUs). Using the proposed scheme, minimal PMUs are installed in existing power transmission networks so that the fault, if it occurs, can be located correctly in the network. The scheme combines the fault-location algorithm and the fault-side selector. Extensive simulation results verify the proposed scheme.

A New Fault Locator for Three-Terminal Transmission Lines Using Two Terminal Synchronized Voltage and Current Phasors

With the advent of the high synchronization accuracy of modern phasor measurement units (PMUs), a new approach for accurately locating faults on three-terminal lines is proposed. Using the data measured from two terminals of three-terminal lines, the proposed technique can provide an extremely accurate fault location. The EMTP/ATP simulator is used to demonstrate the performance of the proposed fault locator. The simulation results show that the accuracy of fault location is very high under various fault resistance, fault locations, prefault loading conditions, source impedance, and fault types.

A new method for power signal harmonic analysis

With the increasing use of nonlinear loads in power systems, the harmonic pollution becomes more and more serious. It is well known that fast Fourier transform (FFT) is a powerful tool for power signal harmonic analysis, but leakage effect, picket fence effect, and aliasing effect make FFT suffer from specific restrictions. In this paper, we proposed a new method for power signal harmonic analysis. The major components of this method are a frequency and phasor estimating algorithm, a finite-impulse-response comb filter, and a correction factor. We also combine other methods to enhance our performance, such as discrete Fourier transform and least square error (LSE) method. To verify this method, we provided the comparisons of this method with FFT.

A Fault Location Technique for Two-Terminal Multisection Compound Transmission Lines Using Synchronized Phasor Measurements

This paper presents a fault location technique for two-terminal multisection compound transmission lines, which combine overhead lines with underground power cables, using synchronized phasor measurements acquired by global positioning system (GPS) based phasor measurement units (PMUs) or digital relays with embedded PMU or by fault-on relay data synchronization algorithms. The technique is extended from a two-terminal fault location method with synchronized phasor measurements as inputs. A novel fault section selector is proposed to select the fault line section in advance. The proposed technique has the ability to locate a fault no matter where the fault is on overhead line or underground power cable. The adopted technique has a solid theoretical foundation and is direct and simple in terms of computational complexity. Both extensive simulation results and field test results are presented to demonstrate the effectiveness of the proposed scheme. The proposed technique has already been implemented in the Taiwan power system since the year 2008. Up to the present, the proposed technique yields excellent performance in practice.

A fault detection and faulted-phase selection approach for transmission lines with Haar wavelet transform

Wavelet transform is a novel signal processing technique and has been widely used in many applications, including power system disturbance analysis. Many published works introduce the wavelet transform as a tool to analyze power system disturbances. In this work, a dyadic wavelet transform based approach, which is used to detect transmission line faults, is proposed. The coefficient of discrete approximation of the dyadic wavelet transform with Haar wavelet is used to be an index for transmission line fault detection and faulted-phase selection. Basic ideas and the proposed algorithm are described in this paper. MATLAB/Simulink is used to generate fault signals and verify the correctness of the algorithm. Simulation results reveal that the performance of the proposed fault detection indicator is promising and easy to implement for computer relaying application.

Detection and Correction of Saturated Current Transformer Measurements Using Decaying DC Components

When fault currents contain decaying dc components, current transformers (CTs) face the risk of becoming saturated. Traditionally, fault current waveform or CT model analyses were used to detect CT saturation. This paper analyzes the decaying dc components in fault currents to detect CT saturation. The decaying dc component in fault currents is first estimated using phasor-based computations. Such a component is then used to define a detection index. The proposed detection index can be easily used to detect CT saturation because its value in an unsaturated period is within a pre-known range. After CT saturation has been detected, the current samples and phasors in the latest unsaturated period are used to correct the saturated current samples. The proposed algorithm was tested using MATLAB/SIMULINK simulator and realized on a DSP Starter Kit to demonstrate its effectiveness and applicability.

A reiterative DFT to damp decaying DC and subsynchronous frequency components in fault current

This work presents a reiterative discrete Fourier transform (DFT) algorithm for fault current filtering. First, the short-windows DFT (SWDFT)-based mimic filter is developed to damp the measurement. Then, a reiterative scheme is proposed to reconstruct the damped measurement for further damping. The proposed algorithm can sufficiently damp the decaying dc as well as the subsynchronous frequency components. Thus, the proposed algorithm is appropriate to the filtering design on both the conventional and series-compensated transmission lines. Meanwhile, the recursive form is developed to reduce the computational burden. The simulation results illustrate that the algorithm significantly reduces the time to obtain the accurate fundamental phasor and that it has a better performance than the conventional DFT algorithm

An Unsynchronized Measurements Correction Method for Two-Terminal Fault-Location Problems

This paper presents a method to correct the unsynchronized measurements for two-terminal fault-location problems. First, a synchronization index is defined to check whether the measurements are synchronized. A modified secant method-based algorithm is then developed to obtain a synchronization angle and correct the unsynchronized measurements. When the unsynchronized measurements are corrected, the fault location can be simultaneously obtained from the intermediate result of the proposed computation. Thus, although the proposed method is developed to correct the unsynchronized measurements, the fault-location problem can also be solved. Compared with the previous works, the proposed iteration equation is simpler. The MATLAB/SIMULINK simulator is used to evaluate the effectiveness of the proposed method.

A fault location algorithm for transmission lines with tapped leg-PMU based approach

This work presents a new fault location algorithm for transmission lines with tapped legs. For the transmission lines connected with short interim tapped leg on the midway, the conventional multi-terminals fault location algorithms are inappropriate for these systems. The proposed fault location algorithm only uses the synchronized phasors measured on two terminals of the original lines to calculate the fault location. Thus, the existing two-terminals fault locator can still be used via adopting the now proposed algorithms. Using the proposed algorithm, the computation of the fault location does not need the model of tapped leg. The proposed algorithm can be easily applied to any type of tapped leg, such as generators, loads or combined systems. EMTP simulation of a 100 km, 345 kV transmission line have been used to evaluate the performance of the proposed algorithm. The tested cases include various fault types, fault locations, fault resistances, fault inception angles, etc. The study also considers the effect of various types of tapped leg. Simulation results indicate that the proposed algorithm can achieve up to 99.95% accuracy for most tested cases.