A bus differential protection scheme using real-time synchrophasor data

To enhance power system dependability and efficiency, it is of great importance to obtain correct parameters of the models of key power system components such as a synchronous generator (SG). Technology of synchronized phasor measurements allows us to estimate the SG model parameters through measurements in power system steady states and transients states, without switching the SG off and conducting complex testing procedures. The theory of electric circuits and electric machines, theory of optimization and statistics, and matrix algebra are applied in this study. The developed parameter estimation method has been implemented in the MATLAB software. The method has been verified through real-world measurements captured by a phasor measurement unit installed at a large power plant in the United Power System. This paper presents an algorithm of the turbogenerator synchronous reactance estimation via a set of synchrophasor data taken under steady-state conditions. Also, the paper considers the criteria for an appropriate data array ensuring successful parameter estimation. An algorithm has been developed and implemented in MATLAB software package. To improve the parameter estimation accuracy, an algorithm has been proposed to modify a nominal value for the SG no-load excitation current depending on the heating of the field winding. The algorithm has been successfully tested out based on a set of steady state synchrophasor data captured for one of the turbogenerators in the Russian United Power System. The authors have developed and analyzed quantitative criteria to determine a set of measured parameters of steady-state modes, providing the most accurate results of the turbogenerator synchronous reactance. The developed algorithm allows accurate update of the turbogenerator synchronous parameters through synchrophasor measurements recorded in a steady state modes of electric power systems. Using the criteria for selecting phasor data, it seems possible to automate the process of generating a data array of measurement of various steady-state modes necessary for identification. The proposed procedure that considers the field winding temperature can be employed in math models to estimate SG transient and subtransient parameters based on phasor measurements in transient modes of electric power systems.

RELEVANCE. Recently, along with the initial scope of synchronized vector measurements (synchrophasor) technology associated with Wide Area Measurement System (WAMS), more and more attention is paid to expanding the scope of this technology. Digital substations are one of the places for generating synchrophasor signals, at the same time, synchrophasor data are proposed to be used for the purposes of relay protection and automation at the digital substations itself, which will facilitate the construction of centralized relay protection systems at the substation. THE PURPOSE. Consider the use of synchrophasor technologies at a digital substation of the fourth type, as a replacement for Sampled Values (SV) signals. Consider additions to the standard set of synchrophasor signals necessary for the operation of various relay protections at a digital substation. Perform an analysis of the accuracy of calculating the synchrophasor when the frequency of the controlled current and voltage changes relative to the nominal value, when higher harmonics appear in the measured signal. Develop a pre-computation technique for relay protection algorithms. METHODS. When solving the problem, the method of calculating the total measurement error of the synchrophasor TVE (Total Vector Error) was used - a value that characterizes the deviation of the amplitude and phase of the measured vector from their specified values. CONCLUSION. The use of synchrophasor signals with the necessary additions for the operation of relay protection reduces the load on the digital network of the digital substation, simplifies the operation of relay protection algorithms. Calculations have shown that the measurement errors of synchrophasor do not go beyond the specified parameters. The proposed methods of precomputation allow to speed up the work of relay protection algorithms.

Performance analysis of a DNN classifier for power system events using an interpretability method

There have been quite a few attempts to compute synchronous generator parameters based on voltage and current synchrophasors taken under power system transients. However, we have not seen any publications with thorough analysis as to how soon the phasor measurement unit reacts to disturbance conditions, which components of the transient are filtered out and which are passed through, as well as what the total vector error is. The goal of this research is to determine all of these characteristics of a phasor measurement unit when playing back transient oscillograms for a stator short circuit obtained through mathematical modeling. The transient oscillograms have been derived via both a full Park-Gorev system of flux linkage equations as well as the MATLAB/Simulink Synchronous Machine block. Physical modeling was then conducted via a real-time digital simulator (RTDS) along with a dedicated phasor measurement unit ENIP-2 (PMU), and the stator current phasors were recorded. Our analysis has shown that both RTDS and ENIP-2 (PMU) almost entirely filter out the exponentially decaying DC component of the fault current while closely following the periodical signal envelope. The total vector error has been estimated to become below 1–2 % after around 0,02–0,03 s into the fault when selecting the “P” class filters according to IEEE C37.118. We have come to a conclusion that synchrophasor measurements under power system disturbances could be utilized for estimating the synchronous, transient, and subtransient generator parameters. The selected synchronous machine model in the form of flux linkage equations is correct, as the obtained transient oscillograms are exactly the same as those produced by Simulink. “P” class phasor measurements can be recommended for representing transients in the stator circuit of a synchronous generator. The results of this investigation are meant to be employed for synchronous machine parameter estimation based on phasors sourced from RTDS and, hopefully, from phasor measurement units installed at power plants.

An eigensystem realization algorithm based data-driven approach for extracting electromechanical oscillation dynamic patterns from synchrophasor measurements in bulk power grids

Voltage instability has caused a great deal of concern in the existing power systems. Despite best efforts, it is still not uncommon a phenomenon and has caused some of the major blackouts and catastrophic failures in the recent past, resulting in huge social and economic losses. The advent of synchrophasor technology has made possible wide-area measurements in real-time, and has found huge applications in power systems. The identification of subregions in power systems that experience a unique voltage instability problem is one of the most important steps of voltage stability analysis. This paper presents a method to identify voltage control area (VCA), based on coherent groups of buses, using system states obtained from synchronized phasor measurements. The coherency is identified by applying hierarchical clustering, a machine learning technique. The coherent buses are identified by applying the machine learning technique on the angles obtained from bus voltage phasors. The results so obtained using the data from Phasor Measurement Units (PMUs) on 10-machine, 39-bus New England power system model are presented.

Since transmission lines are crucial links in the power system, one line outage event may bring about interruption or even cascading failure of the power system. If a quick and accurate line outage detection and localization can be achieved, the system operator can take necessary actions in time to mitigate the negative impact. Therefore, the objective of this paper is to study a method for line outage detection and localization via synchrophasor measurements. The density of deployed Phasor Measurement Units (PMUs) is increasing recently, which greatly improves the visibility of the power grid. Taking advantage of the high-resolution synchrophasor data, the proposed method utilizes frequency measurement for line outage detection and power change for localization. The procedure of the proposed method is given. Compared with conventional methods, it does not require the pre-knowledge on the system. Simulation study validates the effectiveness of the proposed method.

This chapter first introduces the basic theories of power system relay protection, summarizes the functions and basic requirements of relay protection, and illustrates the basic principles of relay protection. The basic task of relay protection is to identify the fault and quickly clear it, and to ensure that the non‐faulty part can continue in normal operation. Relay protection with good performance should meet the requirements of reliability, selectivity, speed and sensitivity. In order to meet the requirements of a complex network, relay protection principles with better performance must be applied, among which is distance protection. Compared with distributed substation area protection, substation centralized protection could acquire more information, locate the fault from the whole station level, simplify the cooperation of protection operating time and also improve the selectivity and reliability of protection, which is beneficial for intelligent protection decision‐making.

Highly reliable overcurrent protection scheme for highly meshed power systems

This paper designs an electronic substation simulation relay protection device with load check. At the same time, the device is studied and applied in the new substation. First of all, this paper analyzes the primary wiring mode and three-phase symmetrical current and voltage in the primary side of a typical substation, and confirms the transformer ratio, polarity and wiring mode of the current/voltage transformer. Then, by checking the polarity of line protection, metering, bus protection, main variable differential protection and backup protection, the polarity error of metering circuit with load check protection and metering circuit is effectively avoided. Finally, through the field test verification in the new 220kV Fuxing station of Jinzhou power supply company, it is verified that the technology adopted in this paper can fully meet the requirements of substation simulation load test. The relay-protection device with load check designed in this paper solves the problem that the conventional electric-type single-phase large-current generator can only detect the transformer ratio and polarity of the relative single-phase loop current transformer, and the difference loop cannot be detected. It shortened the switching operation time of changing ratio, polarity and phase check of the primary and secondary circuits after passing the load of the substation transmission belt.

In this paper a new method is presented for voltage sag source location based on directional overcurrent (DOC) relay information. In this method the current (during sag and presag) is the only variable which is measured by relay/power quality (PQ) monitor. Then relative location of voltage sag source is determined using the variation of the magnitude of measured current positive-sequence component and the sign of its phase-angle jump. The performance of the proposed method is compared with distance relay (DR) and phase change in sequence current (PCSC) methods by using PSCSD/EMTDC and MATLAB on a large scale actual regional network including transmission and sub-transmission levels. The results show the good performance of the new method and its unique applicability in cases where only currents are recorded.

The Flexible AC Transmission System (FACTS) devices are used in modern electric power system to increase the capacity of the transmission lines and dynamic/transient stability limits. However, the FACTS devices cause mal-operation of the protective relays. So, the protective relaying schemes of transmission lines must be modified for achieving grid security and integrity. This paper studies the influence of the reactive power compensation on the performance of the Mho distance relays used to protect transmission lines. It deals with UPFC impact on the Mho distance relay using analytical and simulation techniques. Then, an adaptive Mho relay is developed in MATLAB/Simulink environment based on Phasor Measurement Units (PMUs). The developed Mho relay is used to exclude the effect of the UPFC in the fault loop. The performance of the adaptive relay is compared with the conventional Mho relay. The results prove the reliability and viability of the proposed adaptive relay.

State estimator is an important tool for online monitoring, analysis and control of power systems. With the increased use of phasor measurement units in a power grid, utilization of synchro phasor measurements in State Estimation (SE) becomes essential. Conventional State Estimation (CSE) has been done from measurements obtained by Supervisory Control And Data Acquisition (SCADA) systems. Linear State Estimation (LSE) is done using phasor measurements alone. The paper presents a hybrid method called Two Stage State Estimation (TSSE), wherein the states of the system are estimated by incorporating both the SCADA measurements and phasor measurements. Simulations are done on IEEE 14 bus, IEEE 30 bus and IEEE 118 bus systems and results are compared.

This paper introduces a novel approach for power system fault diagnosis based on synchronized phasor measurements during the fault. The synchronized measurements are obtained in real time from Phasor Measurement Units (PMUs) and compared with offline thresholds determined by decision trees (DTs) to diagnose the fault. The DTs have already been trained offline using detailed power system analysis for different fault cases. While the traditional methods for fault diagnosis use the status of protective relays (PRs) and circuit breakers (CBs) to infer the fault section in the power system, the proposed method uses the available signals following the fault and thus can be trusted even in case of protection system failure. Therefore, fault diagnosis can be achieved successfully especially in blackout situations, where many CBs and and/or PRs malfunction. Simulation results on the IEEE 118-bus test system show that the proposed method is highly accurate in wide area fault diagnosis in spite of incomplete system observability.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A traditional distance protection relay uses a lumped parameter model of the transmission line. For a long 1000-kV UHV line with large distributed capacitance, such a simplified line model is inadequate and can cause malfunction of the relay due to large errors in the impedance measurement. This paper presents a new line model for a distance relay and the procedure of reliable fault impedance measurement and relay setting. It describes the proposed application of the relay developed to a 645-km 1000-kV UHV transmission line including shunt reactor compensation, which is currently being constructed in China. Tests are carried out on an RTDS (real time dynamic system) to evaluate the relay performance, showing significant improvement compared to a more traditional distance relay. The new distance relay is shown to satisfy the requirement of 1000-kV UHV transmission line protection. </para>