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The grid-connected converter synchronizes with the power grid through the controller, so its out-of-step mechanism and out-of-step characteristics are different from synchronous generators. The out-of-step characteristics and out-of-step protection of grid-connected converter are urgent research topics at present. In this paper, the out-of-step mechanism of grid-connected converter under the low voltage ride through (LVRT) control strategy is analyzed by combining the phase plane method and the equal area criterion. The characteristics of current, voltage and measured impedance angle at the point of interconnection (PoI) are analyzed after the grid-connected converter is out-of-step, and compared with those of the traditional power system. On the basis of these, a novel out-of-step protection method for the grid-connected converter is proposed based on the measured impedance angle at the PoI. It judges the out-of-step by the characteristic that the measured impedance angle oscillates continuously and the difference of its extreme values increases gradually. The faster the out-of-step oscillation develops, the faster the protection acts, so it is adaptive. Finally, a MATLAB/Simulink simulation model is built to verify the effectiveness of the proposed protection method.

Modern distance relays have integrated numerous protection functions, including power-swing blocking and out-of-step or pole-slip tripping functions. The main purpose of the power-swing blocking function is to differentiate faults from power swings and block distance or other relay elements from operating during stable or unstable power swings. Most power-swing blocking elements are based on traditional methods that monitor the positive sequence impedance rate. The required settings for the power-swing blocking elements could be difficult to calculate in many applications, particularly those where fast swings can be expected. For these cases, extensive stability studies are necessary to determine the fastest rate of possible power swings. This paper presents a detailed step-by-step method for settings calculation of out-of-step (OOS) protection, both blocking and tripping functions considering a generic two-source system. Then the method is applied to define the protection relay settings installed at the interconnection between the Russian and Mongolian power systems, as it is crucial to feed the demand-rich Mongolian power system. In this paper, a specific impedance method is used for defining the OOS protection settings. This paper innovates by testing the settings using the recordings of the major events of 15 September 2018 in two approaches: hybrid co-simulation and cyber-physical. Both tests have demonstrated the appropriate performance of the proposed settings and proving the proposed methodology works appropriately.

Shunt faults may cause significant fluctuations in the electrical output of the Synchronous Generators (SGs), leading to a loss of synchronization with the remaining power network. Electrical power analysis and the Durbin Watson (DW) statistic can be manipulated to diagnose the instability of the power quality parameters, and to discern between synchronous and asynchronous running of the generator. In this research, the computational techniques serve as a proper foundation of intelligent relay to anticipate and detect the generator Out-of-Step (OOS) situation following the fault presence. The protection strategy can identify sudden variations in several electrical waves in the OOS conditions, such as phase voltage, current, active power, reactive power, and power angle. To verify the performance of the method, a power model with real parameter data of its components is built using the software package of the Alternative Transient Program (ATP). The advanced algorithm is carried out and analyzed using the MATLAB application. Simulation results and analysis show that the protection plan has the ability to recognize the OOS events upon which the protective relay emits a tripping signal to both the annunciation panel and the generator circuit breakers. Whereas, it remains idle under acceptable synchronization conditions. As a consequence, the OOS is rapidly announced before the second pole-slipping occurrence. Furthermore, the algorithm is robust during the stable power swings, and the property of the protection redundancy is provided in this strategy. Additionally, it has the capability of estimating both the instability time and the frequency rate of the unstable power swings.

From time to time, a series of unpredictable and conflicting contingencies can lead to angular instability of the power system and even blackouts if not adequately handled by an out-of-step (OOS) protection system. The key contribution of this research work, to the theory of out-of-step protection, is the identification and isolation after a given disruption of many unstable swings. This paper presents a proposed method to avoid false operation for distance function by out-of-step blocking to improve the system stability by using optimally placed PMUs for the fast detection of system analogue quantities. The studies were performed on a modified Eskom transmission network in the Western Cape with 765 kV and 400 kV voltage levels. The aim is to investigate the IEC 61850-90-5 standard for predictive dynamic stability maintaining systems using PMUs for out-of-step conditions of synchronous generators. The power system modelling and simulation are performed in the RSCAD-FX for the proposed multi-area power system network. An experimental lab-scale implementation is built to test the proposed out-of-step algorithm in a real-time digital simulator. Software-based PMU is incorporated to test and validate the IEC 61850-90-5 standard sampled values. Simulation and experimental results are presented.

Modern gas-turbine units (GTUs) and gas-reciprocating units (GRUs) have found a wide use at power plants, including distributed generation facilities, running on gaseous fuel. The design features of these generating units have a considerable effect on the nature and parameters of transient processes due to emergency disturbances in the adjacent network. The study shows that single-shaft gas-turbine and gas-reciprocating units do not allow even short-term considerable frequency drops. These schemes and operating conditions arise due to emergency active power shortages when the connection between the power plant and the power system weakens due to repair conditions or islanded operation. The paper presents the results of transient process calculations for operating power plants (distributed generation facilities), which make it possible to identify the unfavorable properties of GTUs and GRUs. The results show that two-shaft (three-shaft) GTUs and GRUs can switch to out-of-step conditions even when short-circuits in the adjacent network are cleared with high-speed relay protection devices. The features of out-of-step conditions and the admissibility of their short-term duration for the spontaneous restoration of generators’ synchronization are considered. The findings suggest that considering the fundamental design features of generating units provides informed technical decisions on equipping power plants (distributed generation (DG) facilities) and the adjacent network with efficient emergency control systems.

Although the power system usually always appears stable and reliable to consumers, a lot of work and research goes into keeping the power system both stable and reliable under constantly changing conditions and in these increasingly demanding times. One of the key issues in the power system is maintaining stability after large disturbances in order to prevent the loss of synchronicity of the generators in the system. Today’s generator protection systems mostly use measurements of impedance change to detect generator out of step. This article discusses the possibility of detecting the loss of synchronicity by using real time load angle measurements. The authors propose a real time load angle measurement algorithm and present the results of the algorithm’s testing performed on a real hydrogenerator. The results show that the developed algorithm gives highly accurate real time load angle measurements with the maximum possible resolution and that the load angle can be used for detecting the synchronous generator out of step.

In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing is developed. The algorithm based on theoretical background described in this paper is backed up by the data and results from corresponding simulations done in Matlab environment. Presented results aim to provide the insights of the potential benefits, such as fast and efficient detection and reaction to angle instability, this algorithm can have on the improvement of the power system protection. Accordingly, suggestion is given how the developed algorithm can be implemented in protection segments of the WAMPAC systems in the transmission system operator control centers.

In the 21st century, the worldwide concern about global warming has forced energy to transform in the direction of low-carbon and non-carbon. The utilization of renewable energy is developing rapidly, which makes the non-synchronous generator sources become the main part of the newly added power sources. Based on the fundamentals of AC power grid operation, this paper describes three technical challenges faced by the power system in transition: the inadequacy of the classic synchronization stability concept in representing the new synchronization connotation of AC power systems with large proportion of non-synchronous generator sources; the inapplicability of the electromechanical transient analysis method in analyzing the generalized synchronization stability; and the wideband resonance instability caused by negative resistance of power electronic equipment. The decisive factors for maintaining the generalized synchronization stability, the countermeasure to solve the inapplicability of the electromechanical transient analysis method and a systematic approach to tackle the broadband resonance instability are proposed in the paper.

Despite having extensive research dedicated towards designing methodologies for synchronous out-of-step detection, the risk posed by a large-scale power blackout still makes power system protection an active research area. In recent decades, multiple out-of-step detection techniques such as impedance-based relays and equal-area criterion-analysis-based methods have been widely adopted. However, these conventional techniques have been known to suffer from drawbacks that may be attributed to the inherent assumptions of their foundational design principles. Therefore, to alleviate some of the problems faced in the currently adopted techniques, researchers have been studying the implementation of estimation algorithms for synchronous out-of-step detection. Aiming to contribute to this research area, this paper proposes a synchronous out-of-step detection algorithm that uses a deep Q-network-based disturbance observer, robust to measurement noise. Using the disturbance estimation provided by the observer and a separately gathered critical clearing time data of the power grid, a neural network is trained to relate the magnitude of the estimation with the critical clearing time. The trained neural network is then used to provide an estimation of the critical clearing time for the algorithm, which uses the information to predict whether a fault will result in a stable power swing or a synchronous out-of-step detection. The performance of the proposed algorithm is verified through a real-time digital-simulator-based hardware-in-the-loop simulation. The results show that the proposed algorithm can detect synchronous out-of-step prediction by estimating the disturbance resulting from line fault within two cycles and predicting the critical clearing time at sample fault locations within a 3% margin of error.

Out-of-step protection of one or a group of synchronous generators is unreliable in a power system which has significant renewable power penetration. In this work, an innovative out-of-step protection algorithm using wavelet transform and deep learning is presented to protect synchronous generators and transmission lines. The specific patterns are generated from both stable and unstable power swing, and three-phase fault using the wavelet transform technique. Data containing 27,008 continuous samples of 48 different features is used to train a two-layer feed-forward network. The proposed algorithm gives an automatic, setting free and highly accurate classification for the three-phase fault, stable power swing, and unstable power swing through pattern recognition within a half cycle. The proposed algorithm uses the Kundur 2-area system and a 29-bus electric network for testing under different swing center locations and levels of renewable power penetration. Hardware-in-the-loop (HIL) tests show the hardware compatibility of the developed out-of-step algorithm. The proposed algorithm is also compared with recently reported algorithms. The comparison and test results on different large-scale systems show that the proposed algorithm is simple, fast, accurate, and HIL tested, and not affected by changes in power system parameters.