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Changes in consumption and changes in the structure of the system always occur in each power system. One of the effects of these changes can be the instability of the system voltage. When voltage is unstable, their performance is in conditions of power fluctuations after large errors occur. Determining the voltage stability of traditional methods is time consuming and does not have the necessary efficiency for instantaneous monitoring. In this paper, an index based on the changes of two indices of frequency deviation and frequency response of inertia in the time after the occurrence of perturbation is presented, which has the ability to detect the occurrence of instability and at the same time high speed timely estimation of voltage instability in the power system. In addition, this indicator has been used to determine the appropriate time to start load removal (voltage reduction load). All simulations are performed on the IEEE 33-bus network in DIgSILENT software, the results of which indicate that the proposed index has a very low computational load. Because the proposed method for instantaneous voltage instability prediction does not depend on the network structure and load model and does not require any threshold value. Therefore, the proposed index has a very low computational load. These advantages make the proposed method an interesting option for online and practical applications.

In distribution networks with arc suppression coil grounding, the fault line can be set as the energy leakage channel of the capacitive current of the entire system. During the period from fault occurrence to the whole action process of arc suppression coil, there is abundant fault information in the transient waves. However, the data of this period are usually ignored in previous methods. In this study, a novel fault section location method based on the leakage energy function is proposed. Only the fault phase voltage and fault phase current are used in the proposed method, to avoid the difficulty of the zero‐sequence current measurement. Then, the action characteristics of two types of arc suppression devices are analysed. The influence of the capacitor current on the fault phase voltage and current during the entire process of arc suppression coil operation is deduced. The difference between the leakage energy on both sides of the fault section is used as the criterion for fault section location. Finally, the effectiveness of the method is verified by a case study. The simulation results indicate that the proposed method has high sensitivity and high impedance adaptability, that will have more advantages in the actual situations.

Changes in consumption and changes in the structure of the system always occur in each power system. One of the effects of these changes can be the instability of the system voltage. When voltage is unstable, their performance is in conditions of power fluctuations after large errors occur. Determining the voltage stability of traditional methods is time consuming and does not have the necessary efficiency for instantaneous monitoring. In this paper, an index based on the changes of two indices of frequency deviation and frequency response of inertia in the time after the occurrence of perturbation is presented, which has the ability to detect the occurrence of instability and at the same time high speed timely estimation of voltage instability in the power system. In addition, this indicator has been used to determine the appropriate time to start load removal (voltage reduction load). All simulations are performed on the IEEE 33-bus network in DIgSILENT software, the results of which indicate that the proposed index has a very low computational load. Because the proposed method for instantaneous voltage instability prediction does not depend on the network structure and load model and does not require any threshold value. Therefore, the proposed index has a very low computational load. These advantages make the proposed method an interesting option for online and practical applications. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel state and a fault estimation scheme for a class of hyperbolic spatiotemporal dynamic systems in the presence of unknown external disturbance. They consider the occurrence of multiplicative actuator and sensor faults. In detail, they consider two cases of fault occurrence: (i) only one type (actuator or sensor) of fault happens; (ii) two types of faults occur simultaneously. This study discusses the fault detectability conditions by proposing a fault detection observer. To complete the estimation problem, three difficulties arise: (i) no prior information shows the type of faults; (ii) the observer design is non-linear due to multiplication between plant signals (state or input) and unknown fault parameters; (iii) only one boundary measurement is available. They convert the original faulty plant into its observer canonical form. By proposing two filters based on the resulting observer canonical form, they develop novel parameter update laws for fault parameter estimation. With the proposed update laws, the true state of the faulty plant can be estimated by the proposed observers. By selecting appropriate Lyapunov functions, they prove that estimation error of state and fault parameters exponentially decays to an arbitrarily small neighbourhood of zero despite unknown external disturbance.

In distribution networks with arc suppression coil grounding, the fault line can be set as the energy leakage channel of the capacitive current of the entire system. During the period from fault occurrence to the whole action process of arc suppression coil, there is abundant fault information in the transient waves. However, the data of this period are usually ignored in previous methods. In this study, a novel fault section location method based on the leakage energy function is proposed. Only the fault phase voltage and fault phase current are used in the proposed method, to avoid the difficulty of the zero-sequence current measurement. Then, the action characteristics of two types of arc suppression devices are analysed. The influence of the capacitor current on the fault phase voltage and current during the entire process of arc suppression coil operation is deduced. The difference between the leakage energy on both sides of the fault section is used as the criterion for fault section location. Finally, the effectiveness of the method is verified by a case study. The simulation results indicate that the proposed method has high sensitivity and high impedance adaptability, that will have more advantages in the actual situations. [ABSTRACT FROM AUTHOR]

Types I, III and IV wind distributed generators show different and wide range of current sharing capacity during the occurrence of faults in the distribution feeders. In a hybrid microgrid consisting of any of the above mentioned types of wind distributed generators and photovoltaic distributed generators, the fault current in a feeder shows different behaviour which changes as per the type of distributed generators, grid/islanded connection of microgrid operation, distance of the fault from the point of common coupling and nature of the loads in the microgrid system. The novel contribution of this paper is the implementation of a fuzzy logic based adaptive protection scheme through analysis of the q0 components of fault current which are used to detect the low X/R ratio of distributed generators, modes of operation, transient reactance during the series and shunt faults in types I, III and IV wind turbines and PV integrated hybrid microgrid. Considering q0 components and transient reactance, a new relation between the relay current settings and modes of operation has been identified for adaptive relaying. The effectiveness of the proposed adaptive protection scheme for the hybrid microgrid is verified through a simulation case study using Matlab -Simulink software. [ABSTRACT FROM AUTHOR]

Doubly fed induction generator (DFIG) is the most popular machine for the wind power application that consists of the ability for variable speed operation and reactive power control with the help of power electronics converters. It is one of the prominent system that follows grid code requirement as it remains connected with the grid even during the fault occurrence. For making the DFIG continuity in the grid, low-voltage ride through or fault ride through (FRT) techniques are used. Fault current limiter is one of the major schemes used under the FRT. A saturated core fault current limiter (SCFCL) is used in DFIG system to enhance the FRT capability. The main property of SCFCL is the change in permeability between the saturated and unsaturated conditions of the magnetic core to concurrently provide low steady-state impedance and high transient fault impedance for limiting the fault current.

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line.

In this research, the objective is using 4 quadrotors in a group to carry out a certain weighted load. The load is connected by cables to each quadrotor. The equations of motion of the quadrotors are considered completely and without simplification. Unlike other researches, to express the relationship between the load and the quadrotors, the ropes are considered as springs, so they are pulled out and retracted during the mission. Formation control design and path tracking by the group is done by using feedback linearization control. Control protocol design is presented in two structure, centralized, and decentralized. Unlike other papers, in decentralized structure, there is no information communication between the agents to reduce the communication costs. The mission of the group is defined as the quadrotors first pick off the load from the ground and, then, track the desired path to reach the target point. When the load reaches the target point, the quadrotors should put the load on the ground and, then, land themselves. Cutting the cable of one of the quadrotors is applied to the system as a fault and in addition to providing a method to detect its occurrence, the performance of the centralized controller is checked in this situation. [ABSTRACT FROM AUTHOR]

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line. [ABSTRACT FROM AUTHOR]

This study presents a generalised fault diagnosis method for power transistors in the asymmetric half‐bridge power converter of switched reluctance motor (SRM) drive. In order to extract the remarkable fault features, three current sensors are rearranged. Each phase current can be calculated by solving the equations associated with the detected values of three current sensors and three coefficients obtained based on different switching states. Different faults are preliminarily detected by monitoring the error between the estimated bus current and the actual bus current. After the identification of fault occurrence, the error will be calculated with all the combinations of three coefficients. The minimum error will be found and the corresponding coefficients are recorded. The fault types and fault power transistors are located by comparing the actual coefficients with the recorded coefficients. Being different from the existing methods, the developed diagnostic strategy can detect multiple fault types and can be used in different control modes, including voltage pulse width modulation, current chopping control and angular position control schemes. Moreover, the proposed technique is easy for online implementation without extra sensors and additional electric devices. The effectiveness of the proposed solution is validated on a three‐phase 12/8 SRM drive. [ABSTRACT FROM AUTHOR]

Buildings consumed about 40% of primary energy and 70% of the electricity in the U.S. It is well known that most buildings lose a portion of their desired and designed energy efficiency in the years after they are commissioned or recommissioned. Majority of the Heating, Ventilation, and Air-Conditioning (HVAC) systems have multiple faults residing in the systems causing either energy, thermal comfort, or indoor air quality penalties. There are hundreds of fault detection and diagnostics (FDD) algorithms available, but there is lacking a common framework to assess and validate those FDD algorithms. Fault modeling is one of the key components of such a framework. In general, fault modeling has two purposes: testing and assessment of FDD algorithms, and fault impacts analysis in terms of building energy consumption and occupants’ thermal comfort. It is expected that fault ranking from the fault impact analysis can facilitate building facility managers to make decisions. This paper provides a detailed review of current state-of-the-art for the fault modeling of HVAC systems in buildings, including fault model, fault occurrence probability, and fault simulation platform. Fault simulations considering fault occurrence probability can generate realistic faulty data across a variety of faulty operating conditions, and facilitate testing and assessment of different FDD algorithms. They can also help the fault impact study. Three research gaps are identified through this critical literature review: (1) The number of available fault models of HVAC systems is still limited. A fault model library could be developed to cover all common HVAC faults for both traditional and non-traditional HVAC systems. (2) It is imperative to include the fault occurrence probability in fault simulations for a realistic fault impacts analysis such as fault ranking. (3) Fault simulation platforms need further improvements to better facilitate the fault impact analysis. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems, as distributed energy resources, can adversely affect the coordination of the protection system in distribution circuits. Various approaches have been presented in the literature to solve this problem, but none of them has proposed a solution for the staircase current waveforms seen in PV‐dominated distribution systems. As there is insufficient time to apply new settings to a protection device following a fault, the appropriate solution should be to adaptively modify the characteristic curves in advance of the fault. Accordingly, using the voltage profile as a pre‐fault index for current waveform, this study suggests an adaptive approach to efficiently modify the protection settings before the fault occurrence. To this end, first, an offline technique is used to calculate the best appropriate group setting corresponding to each voltage profile. Second, in real time and according to the voltage profile, an online algorithm applies the predefined group settings to the corresponding protection devices. Simulation results demonstrate the effectiveness of the proposed method on a practical network such that by applying the proposed technique, settings on programmable protection devices can be readily modified to improve on their coordination. [ABSTRACT FROM AUTHOR]

The growth of utilisation of wind turbines in the contemporary power systems, the transient stability (TS) evaluation has turned to a challenging issue in the modern power grids. An innovative and high‐precision real‐time method based on the transient energy function (TEF) is proposed which aims to evaluate the TS of power system in the presence of wind turbines. The proposed method is designed so that the initial point of TEF is calculated precisely by performing offline calculations. Structure preserving is used to guarantee the accuracy of the proposed method in order to consider the details of power system modelling. Moreover, the proposed method takes into account the impacts of the wind turbines controllers utilising new formulation based on a sensitivity‐based approach. The new formulation is utilised to calculate the effects of the controllers reflected in the potential terms of TEF during the fault occurrence. As a result, in addition of considering fault‐on trajectory, the latter technique causes reducing the computational burden and also guarantees accurate real‐time assessment of TS. The simulation results demonstrate the efficiency and also comprehensiveness of the proposed method in calculation of critical clearing time and TS assessment. [ABSTRACT FROM AUTHOR]

For a reliable and stable operation of a power system network, it is important to monitor the dynamics of the system. For this purpose, in real system phasor measurement units (PMUs) have been installed to give information about the grid conditions. Due to a large interconnected non‐linear system, there is a possibility of system collapse due to unusual high stress. Hence, it is essential to detect the generators going out of step at an early stage and separate them. This study presents two algorithms: first one in meant to identify the coherency between the generators in real‐time signal and second algorithm functions to quickly determine the critical generators. The algorithm for coherency identification between the generators uses time–frequency coherency based on smoothed pseudo‐Wigner–Ville distribution signal processing technique. The proposed scheme is validated on several PMUs signals. Further, the Lagrangian method is applied to detect the critical sets of generators going out of step following the severe fault occurrence in the line. This is based on the calculation of energy. The suggested approach discussed in this study can be applied to dynamically reduce a large power system. [ABSTRACT FROM AUTHOR]

In this paper, a novel protection method based on time-time (TT) transform for thyristor-controlled series- compensated lines is presented. First, current signals at both sides of the sending and receiving ends are retrieved and processed through time-time domain transform (TT-transform), and a TT-matrix is produced. A proposed index is then compared with a defined threshold (THD) in order to determine fault occurrence and faulted phases. Within less than three cycles of the fault inception, a tripping signal can be sent that is acceptable for the speed of digital relays. After faulted phase selection, considering the TT-matrix of the faulted phases of both the sending and receiving ends, another index is introduced for estimation of the fault section. Simulation results show that this approach determines fault occurrence, faulted phase, and fault section under different fault conditions such as fault type, fault location, fault resistance, fault inception angle, source impedance, reverse power flow, different levels of compensation, and different locations of the compensator in the line. The test results in the presence of high noise (with SNR up to 15 dB) confirm the effectiveness of the proposed method. The results also indicate that the proposed method is more robust to fault resistance compared to previous studies. [ABSTRACT FROM AUTHOR]

This study presents a time‐varying threshold‐based fault detection (FD) method for a class of single‐input single‐output non‐linear systems in strict‐feedback form with unmeasurable states, unmatched non‐linear fault functions and uncertainties. First, a residual generator with prescribed performance is designed in a framework of recursive technique. Then, the tight time‐varying thresholds are computed by using the prescribed performance bound (PPB) and the FD scheme is presented. Furthermore, the fault detectability is analysed to characterise the sensitivity to the faults. It is shown that the residual signal satisfies the PPB and all the estimation errors are uniformly bounded before fault occurrence. Compared with the method without considering the PPB, the proposed time‐varying thresholds improve the FD performance with fewer false alarms caused by overshoot during the transient process. Finally, a comparative simulation study illustrates the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

Fault occurrence or voltage disturbance, such as mismatch operations or electrical faults caused by structural changes in photovoltaic (PV) panels, local/remote faults, or heavy load operation, can disturb a PV energy conversion system (PVECS) on both the DC and AC sides. On the AC side, any serious disturbance can be isolated using power fuses, overcurrent protection and ground‐fault protection devices. Therefore, the authors propose the use of fractional‐order dynamic‐error‐based fuzzy Petri net (FPN) to detect disturbance events in a microdistribution system. PV energy conversion depends on solar radiation and temperature, and a maximum power point tracking control is used to maintain stable output power and voltage to microdistribution loads. When the desired maximum power is estimated, a bisection approach algorithm is used to regulate the output voltage of the PVECS by adjusting the duty ratios of a buck–boost converter. The maximum power drops, which are compared with meter‐reading power from intelligent meters, are used to detect faults on the DC side. Then, fractional‐order dynamic errors between the desired and estimated powers and a FPN are employed to detect faults. For a small‐scale PVECS, computer simulations are conducted to show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Switched reluctance motors (SRMs) are extensively utilised in electric vehicles (EVs) due to some outstanding capabilities such as rugged and fault tolerant structure. Since the excitation of the phases is performed independently in the SRM, the motor could continue operation even in case of fault occurrence in one of the phases by disabling the faulty phase. However, to improve the reliability of the SRM for EV applications, an efficient fault diagnosis approach should be employed. In this study, an on‐line method for detection of winding inter‐turn short‐circuit fault in the SRMs is presented. The proposed technique is based on a model, in which the extended Kalman filter is utilised. The method achieves a fast response, thus, the remedial strategies could be employed at the initial moments after fault occurrence. The proposed method is simple to implement and reliable in practice. The performance of the proposed approach is verified using some simulations and experiments. The results confirm high capability of the method in different conditions. [ABSTRACT FROM AUTHOR]

Since the internal turn‐to‐turn faults (TTFs), as a common cause of the transformer failures, result in minor changes on terminal currents/voltages, they maybe undetected by the conventional protective relays. In this study, a simple, sensitive and robust linkage flux‐based technique is proposed to protect the power transformers against TTFs. In this approach, some separated multi‐turn windings as search coils (SCs) have to be wrapped around the transformer core legs to sense the related passing flux. Since passing equal flux through a transformer core leg in normal condition induces equal voltages in the related SCs, variation of the induced voltages indicates the fault occurrence in that phase. Against the traditional differential protection schemes, current transformer error and saturation, tap changer operation, energising inrush current, over‐fluxing etc. cannot impact the proposed technique performance. Therefore, it can be introduced as a comprehensive protection technique for power transformers.To confirm the proposed technique performance, it is tested on a real 50 kVA, 20 kV/400 V three‐phase distribution transformer, in various conditions, too. [ABSTRACT FROM AUTHOR]

This study presents the preliminary results of a new methodology for detecting high‐impedance faults in distribution systems based on interharmonic signatures. The methodology involves incorporation of an interharmonic current analysis system into a conventional protection system, such as automatic reclosers and sectionalisers. To check the functionality of the proposed methodology, the authors carried out field tests on different types of soil, involving instantaneous current waveform measurements during the occurrence of faults. The results suggest that the methodology, based on interharmonic currents produced by variations in electric arc length during the occurrence of high‐impedance faults, shows great promise when it comes to detection of the disturbance. [ABSTRACT FROM AUTHOR]

Power restoration schemes incorporated into Distribution Automation (DA) system helps in quickly restoring the power during emergency situations like faults. Due to the numerous advancements made in the distribution system operation in recent times, power restoration analysis needs to be done in a look‐ahead manner based on system wide operational & monitored data apart from just fault data processing during the outages. With the evolution of Advanced Metering Infrastructure (AMI) during recent times, it is now possible to design the look‐ahead restoration schemes by integrating the operation of DA with AMI system using internet protocol based communications, preferably. In this paper, we propose a novel method for power restoration analysis which execute all pre‐defined restoration schemes in a look‐ahead manner by representing distribution system as a weighted graph and computing graph weights based on representation of DA & AMI system's current operational/measured/constraint data from each distribution load segment. Computed graph weights are converted to restoration indices with associated ranking based mechanism to indicate criticality & considerations for each power restoration scheme in case of fault occurrence in real‐time. A case study on the standard RBTS test system has been demonstrated for the proposed method. [ABSTRACT FROM AUTHOR]

This study presents a new method to detect the magnet defects in permanent magnet (PM) machines by calculating the magnet's MMF function from the machine's electrical variables. The authors propose for the first time an inverse transformation to map the winding flux waveform into the corresponding magnet MMF function. The analysis of this function defines the fault occurrence and its position. The winding flux waveform is computed from the electrical variables and this study adopts a reduced order model of the magnetic equivalent circuit to define the direct and inverse transform between the magnet's MMF and the winding flux; for this reason the authors call the new approach the inverse transform method. A dedicated PM machine with a defective magnet has been constructed to validate the proposed method by comparing simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a methodology for calculating the setting impedance of zones 2 and 3 of distance relays is presented, The aim is to reduce protection coordination problems during fault occurrence and changes in the network configuration. The proposed method is based on the impedance seen by the distance relay when faults are simulated on adjacent nodes. The coordination and relay setting is obtained by means of computational algorithms developed to analyze the network topology, determine the pair of primary-backup relays and short circuit studies considering several types of faults in the power system. This process is carried out in an object oriented environment which allows a flexible approach to the user of the software. In the development of this tool search methods based on graph theory were used. The method was applied to an IEEE 14 nodes test system with satisfactory results. [ABSTRACT FROM PUBLISHER]