Power System Protection Applications Research Articles

Assessment and Commissioning of Electrical Substation Grid Testbed with a Real-Time Simulator and Protective Relays/Power Meters in the Loop

Electrical utility substations are wired with intelligent electronic devices (IEDs), such as protective relays, power meters, and communication switches. Substation engineers commission these IEDs to assess the appropriate measurements for monitoring, control, power system protection, and communication applications. Like real electrical utility substations, complex electrical substation grid testbeds (ESGTs) need to be assessed for measuring current and voltage signals in monitoring, power system protection, control (synchro check), and communication applications that are limited by small-measurement percentage errors. In the process of setting an ESGT with real-time simulators and IEDs in the loop, protective relays, power meters, and communication devices must be commissioned before running experiments. In this study, an ESGT with IEDs and distributed ledger technology was developed. The ESGT with a real-time simulator and IEDs in the loop was satisfactorily assessed and commissioned. The commissioning and problem-solving tasks of the testbed are described to define a method with flowcharts to assess possible troubleshooting in ESGTs. This method was based on comparing the simulations versus IED measurements for the phase current and voltage magnitudes, three-phase phasor diagrams, breaker states, protective relay times with selectivity coordination at electrical faults, communication data points, and time-stamp sources.

Transmission Line Parameter Estimation Under Non-Gaussian Measurement Noise

Accurate knowledge of transmission line parameters is essential for a variety of power system monitoring, protection, and control applications. The use of phasor measurement unit (PMU) data for transmission line parameter estimation (TLPE) is well-documented. However, existing literature on PMU-based TLPE implicitly assumes the measurement noise to be Gaussian. Recently, it has been shown that the noise in PMU measurements (especially in the current phasors) is better represented by Gaussian mixture models (GMMs), i.e., the noises are non-Gaussian. We present a novel approach for TLPE that can handle non-Gaussian noise in the PMU measurements. The measurement noise is expressed as a GMM, whose components are identified using the expectation-maximization (EM) algorithm. Subsequently, noise and parameter estimation is carried out by solving a maximum likelihood estimation problem iteratively until convergence. The superior performance of the proposed approach over traditional approaches such as least squares and total least squares as well as the more recently proposed minimum total error entropy approach is demonstrated by performing simulations using the IEEE 118-bus system as well as proprietary PMU data obtained from a U.S. power utility.

Harmonic Phasor Estimation Based on Frequency-Domain Sampling Theorem

Harmonic phasor estimation can be used both in power system protection and monitoring applications, such as islanding detection, high-impedance fault location, and harmonic state estimation. A key challenge for harmonic phasor estimation is that different harmonics have different harmonic frequency bandwidths. As a result, a harmonic phasor estimator (HPE) that can adapt to such variations is needed. Although the sinc interpolation function-based estimator (SIFE) has such ability, it has disadvantages that: 1) it needs numerous simulations to select the model parameter and 2) it cannot obtain zero-error results under nominal frequency condition. In this article, a novel HPE is proposed based on the frequency-domain sampling theorem, where the harmonic phasor is modeled based on several imaginary exponential functions. The proposed HPE is compared with the SIFE in frequency response, model parameter selection scheme, and simulation tests. The results show that the proposed HPE has the following three advantages: 1) it has an easier scheme for model parameter selection; 2) it has zero-error results under nominal frequency condition; and 3) it has higher accuracy under harmonic frequency deviation and harmonic modulation conditions.

Comparison of Various Mother Wavelets for Fault Classification in Electrical Systems

This paper presents a comparative study on mother wavelets using a fault type classification algorithm in a power system. The study aims to evaluate the performance of the protection algorithm by implementing different mother wavelets for signal analysis and determines a suitable mother wavelet for power system protection applications. The factors that influence the fault signal, such as the fault location, fault type, and inception angle, have been considered during testing. The algorithm operates by applying the discrete wavelet transform (DWT) to the three-phase current and zero-sequence signal obtained from the experimental setup. The DWT extracts high-frequency components from the signals during both the normal and fault states. The coefficients at scales 1–3 have been decomposed using different mother wavelets, such as Daubechies (db), symlets (sym), biorthogonal (bior), and Coiflets (coif). The results reveal different coefficient values for the different mother wavelets even though the behaviors are similar. The coefficient for any mother wavelet has the same behavior but does not have the same value. Therefore, this finding has shown that the mother wavelet has a significant impact on the accuracy of the fault classification algorithm.

Harmonic Phasor Estimator for P-Class Phasor Measurement Units

Fast harmonic phasor measurements are very useful in power system protection applications, e.g., high-impedance fault location and intelligent method-based islanding detection. To address this problem, a novel harmonic phasor estimator is proposed in this paper, especially for P-class phasor measurement units (PMUs). The exponential functions are used to model the decaying dc (ddc) component, and the optimal time constant (TC) set for the ddc model is searched based on an enumeration method. In addition, the dynamic harmonic phasors are modeled based on the Shannon sampling theorem. As a result, a filter bank is designed for harmonic phasor and frequency estimations. The rate of change of frequency (ROCOF) of the harmonic is estimated based on a second-order fitting method. The response time of the proposed method for harmonic phasor estimation is always no longer than 40 ms. Simulation test results indicate that the proposed method is more accurate than the Taylor–Fourier transform (TFT) under ddc offset and frequency deviation conditions. In particular, the proposed method is more robust to ddc’s TC variations. An experimental test is implemented to demonstrate the advantages of the proposed method.

Measurement and Analysis of PMU Reporting Latency for Smart Grid Protection and Control Applications

Emerging power system protection and control applications require faster-responding measurements and more accurate knowledge of the actual latency of the measurement and communications systems. A new method for accurately determining the reporting latency of a phasor measurement unit (PMU) has been developed and demonstrated. This method operates in real-time, works passively for any existing PMU without requiring changes to the PMU hardware or software, and it is very accurate - providing a measurement uncertainty of i500 ns in many cases, significantly surpassing the 0.002 s accuracy requirement in the most recent IEEE Synchrophasor standard. Only low-cost hardware and open source software are required. It is particularly important to understand end-to-end system latency, including the impact of local and wide-area communications, rather than just the latency of the PMU device; the proposed method also supports such practical measurements. It is therefore shown how this advance can be used to enable efficient, but realistic, cross-domain power system simulation studies, which incorporate measurement and communications delays. These capabilities address complexity and uncertainty in the design and operation of future PMU-based protection and control functions for new smart grid services.

Power System Frequency Estimation Using Adaptive Accelerated MUSIC

Frequency estimation is vital for monitoring, control, and protection of power systems. Multiple signal classification (MUSIC) method has been used for frequency estimation in communication systems. This method requires wide range of frequency scanning and heavy computations, which is inappropriate for power system applications. This paper proposes an adaptive accelerated MUSIC algorithm for frequency estimation in power systems. The algorithm accelerates the frequency scanning and adapts itself to transient conditions of power systems, to keep the accuracy of the frequency estimation with minimum computations. Experimental signals besides several static and dynamic test signals are used to evaluate and compare the performance of the proposed algorithm with recent methods. These comparisons show that the proposed algorithm provides faster convergence speed, lower computation burden, and more robustness to noise and grid disturbances. These significant advantages make the proposed algorithm appropriate for power system protection and control applications.

Optimal PMU Placement Using Modified Greedy Algorithm

Phasor measurement units (PMUs) provide synchronized measurements of real-time phasors of voltages and currents. It is considered as an important element of the smart wide area measurement system used in advanced power system monitoring, protection, and control applications. This paper proposes a new approach based on a greedy algorithm to solve the optimal phasor measurement unit placement (OPP) problem in the power network. The main purpose of proposed approach is to find out a high-quality solution in a reasonable time that ensures the practicability when applying for a real power network. The OPP problem is solved under both normal operating and contingency conditions. Moreover, some other realistic aspects that may affect the OPP problem, such as PMU channel limitation, zero injection bus, the presence of conventional measurements, are also considered to solve simultaneously. The simulations on IEEE 14-bus, 30-bus, 57-bus, 118-bus test systems, and especially on a large-scale network—the Polish 2383-bus system, are presented for evaluating the feasibility of proposed approach. The results of this study showed that the proposed method is effective and feasible to solve the OPP problem for a real power network.

A Method for Accurate Transmission Line Impedance Parameter Estimation

Real-time estimation of power transmission line impedance parameters has become possible with the availability of synchronized phasor (synchrophasor) measurements of voltage and current. If sufficiently accurate, the estimated parameter values are a powerful tool for improving the performance of a range of power system monitoring, protection, and control applications, including fault location and dynamic thermal line rating. The accuracy of the parameter estimates can be reduced by unknown errors in the synchrophasors that are introduced in the measurement process. In this paper, a method is proposed with the aim of obtaining accurate estimates of potentially variable impedance parameters, in the presence of systematic errors in voltage and current measurements. The method is based on optimization to identify correction constants for the phasors. A case study of a simulated transmission line is presented to demonstrate the effectiveness of the new method, which is better in comparison with a previously proposed method. The results, as well as limits, and the potential extensions of the new method are discussed.

Investigation of Microelectromechanical Switches for Next Generation DC Power Distribution System

Abstract This paper investigates the application of microelectromechanical system (MEMS) switches for DC power distribution system. Traditional electromechanical switches, solid state switches and solid state switch array are studied and simulated to understand their characteristics. Performance and characteristics of MEMS switches are reviewed and identified that electrostatically actuated MEMS switches are suitable for DC power applications. Scalable total cross tied (TCT) array configuration using MEMS switches has been proposed. The proposed configuration is suitable for variable voltage/current rating. Arc-less behavior of the switch configuration is analyzed using modified Paschen’s curve. 400 V/6 A system is considered for the simulation and comparative study. The simulated result of the proposed MEMS switch array configuration is compared with the traditional switches. The comparative study shows that the proposed switch array configuration gives better performance in terms of voltage drop, leakage current, power loss, arc and size. This can be used in DC power system protection, circuit breaking, battery protection and smart grid load switching applications.

Synchronized Phasor and Frequency Measurement Under Transient Conditions

Synchronized phasor measurements are becoming an important element of wide area measurement systems used in advanced power system monitoring, protection, and control applications. The recently issued revised standard C37.118 for synchrophasors has facilitated interoperability of phasor measurement units (PMUs) from different manufacturers. This standard defines performance for compliance when the input signals are in steady state. The performance of PMUs under transient conditions is not considered by the standard at this time, although clearly PMUs will be subjected to inputs under transient conditions. This paper is an attempt to provide the authors' views on how one may approach the question of standardizing PMU response under transient conditions.

DESIGN, IMPLEMENTATION AND TESTING OF AN ARTIFICIAL NEURAL NETWORK BASED ADMITTANCE RELAY

Artificial neural network based technology, which is inspired by biological neural networks, has developed rapidly in the previous decade and has been applied in power system protection applications. Protection of transmission and sub transmission lines is most frequently done using distance relays. This paper discusses the design, implementation and testing of an artificial neural network (ANN) based distance relay that implements characteristics of a mho (admittance) relay. The Artificial Neural Network based designs of distance relays proposed so far work well for faults well within the boundary characteristics of a relay, but are not able to maintain the integrity of the boundaries of the relay characteristics of generic designs.

Design and implementation of low cost reconfigurable data acquisition system for power system protection applications

The design and implementation of a reconfigurable data acquisition system for a digital relay for power system protection applications are described. A 33% power saving and 31% area reduction are recorded when a modified flash analogue-to-digital converter is employed. A further 98% data rate reduction is achieved when the reconfigurable algorithm is applied, enabling an improvement in system efficiency.

Real-time determination of power system frequency

The main frequency is an important parameter of an electrical power system. The frequency can change over a small range due to generation-load mismatches. Some power system protection and control applications, e,g, frequency relay for load shedding, load-frequency controller, require accurate and fast estimation of the frequency. Most digital algorithms for measuring frequency have acceptable accuracy if voltage waveforms are not distorted. However, due to nonlinear devices, e,g, semiconductor rectifiers, electric arc furnaces, the voltage waveforms can include higher harmonics. The paper presents a new method of measurement of power system frequency, based on digital filtering and Prony's estimation method. Simulation results confirm, that the proposed method is more accurate than others, e,g, than the method based on the measurement of angular velocity of the rotating voltage phasor.

Laser-guided discharges in long gaps

Experiments to guide electric discharges with a chain of air breakdown plasmas (plasma channel) produced by a laser were carried out for use in power system protection applications. Electric discharges were guided up to 4.5m with a high power CO/sub 2/ laser focused by a 10m focal length mirror. Unusual 50% flashover voltage characteristics were obtained and the mechanism on the laser-guided discharge is shown. Experiments of laser-guided discharge in fog or rain were also carried out to clarify the effects of precipitation on the guiding characteristics, and the results are analysed quantitatively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Off-Nominal Frequency Measurements in Electric Power Systems

Some power system protection applications require accurate estimates of voltage magnitude and frequency over a wide measurement range. Most digital techniques for measuring frequency have acceptable accuracy over a small range in the neighborhood of the nominal value. This paper presents a method for extending the measurement range of the Least Error Squares (LES) technique. The paper also examines the effectiveness of the technique and presents some results from simulated studies and laboratory experiments. It is essential to maintain the frequency of a power system close to its nominal value. Usually, frequency deviations in the range of two to three percent only are allowed for short durations of time. In this range, the Least Error Squares algorithm (LES) provides accurate estimates and is, therefore, suitable for implementing in most frequency relays. However, the measurement errors increase as the frequency deviation from the nominal value increases. During start-up and shut-down of a generator, its frequency varies over a wide range. If the generator is connected to a transformer, both the generator and the transformer can experience overexcitation. Excessive volts-perhertz (V/Hz) indicates that overexcitation has occurred. One method of estimating this parameter is to measure the voltage magnitude and frequency and then calculate volts-per-hertz. Voltsper-hertz relays that provide accurate measurements over 10 to 70 Hz range would be desirable for use on steam turbine driven generators. The frequency of the voltage of a thermal generator is low during start-up and shut-down procedures.