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A new technique is proposed for loss of field (LOF) detection in synchronous generators (SGs). The proposed scheme employs the variations of SG angular velocity ∆ωφ and load angle ∆δφ to reach this goal, while the mentioned parameters are estimated through air gap flux estimation. The proposed scheme performance is evaluated using realistic simulation case studies based on IEEE C. 37. 102 standard compared to the conventional impedance‐based one. The obtained results show that the presented scheme excels the conventional scheme from speed and security viewpoints. Moreover, the estimation procedure of ∆ωφ and ∆δφ is experimentally validated by using a 10 kVA SG and the results demonstrate that the proposed technique can be easily set and implemented. [ABSTRACT FROM AUTHOR]

The issue of resilience in electrical distribution systems has been proposed increasingly with the frequent occurrence of natural disasters in recent years and the imposition of high costs due to widespread power outages. To date, various resilience indices have been proposed, some of which have been improved upon over time by extensive research, leading to more comprehensive indices. However, a standard index has not yet been approved and presented in this regard by international committees, despite the efforts made. The issue of resilience in electrical networks was examined by curve analysis index in more detail compared to other proposed indices, although it is not yet complete and should be investigated from various aspects and its shortcomings be eliminated. The present study aims to evaluate some fundamental obstacles in the "curve analysis" index and correct it in a new index called "Combining Investment and Reform" (CIR) index. Two issues of "costs in terms of investment and repairs imposed by the event" and "need to separate critical and non‐critical loads" are considered simultaneously in the proposed index. Finally, the capabilities of the proposed index are evaluated and compared in a sample electrical network in the face of events with different intensities. [ABSTRACT FROM AUTHOR]

The transformerless single‐phase semi‐quasi‐Z‐source inverter (SqZSI) has a nonlinear gain curve and requires nonlinear sinusoidal pulse width modulation (NLSPWM) to achieve sinusoidal voltage at the output AC terminal. Although the SqZSI provides some advantages, for example, leakage current elimination, doubly grounded, low volume, and low cost, it needs nonlinear modulation control. The NLSPWM is relatively complex among single‐phase modulation methods and it is considered a disadvantage for this topology, so this paper presents a model‐driven processor programming method that facilitates the implementation of NLSPWM. The developed programming method utilizes a Blockset environment in MATLAB/Simulink to implement NLSPWM, and then the obtained model is compiled and directly uploaded to the ARM Cortex‐M4‐based STM32F4 processor. In this approach, there is no need for coding in C programming language, and only the Simulink mathematical blocks are used so it simplifies the implementation process. The same Simulink model used to model the inverter control is slightly edited for implementation, which accelerates the debugging cycle. Experimental results of 100 W SqZSI confirm the desired and accurate performance of this low‐cost method. The qualitative comparison of the processor programming methods and the performance comparison of the developed SqZSI based on this approach verify the simplicity of implementation. [ABSTRACT FROM AUTHOR]

The subject of resilience in electrical grids has become more popular among researchers in recent decades due to the rise of worldwide natural disasters such as floods, severe storms, snow, and hailstorms as well as the imposition of high costs resulted from widespread outages. Various methods have been proposed to improve the resilience of electrical grids under different conditions. In each work, the authors have validated their proposed method based on a function or metric they have defined to clarify its effect on improving the resilience of electrical grid. However, to date, there is no standardized metric for assessing the resilience of an electrical grid and providing the possibility to compare the many strategies discussed in different papers. This paper tries to explain the metrics that have been presented in various researches in this regard so far, and it compares these metrics from different aspects in order to determine the most comprehensive metric. [ABSTRACT FROM AUTHOR]

Here a new sensitive fault detection criterion is proposed, based on the stationary wavelet transform (SWT) decomposition components of the stator currents, for the online detection of stator winding turn‐to‐turn faults at an early stage of development. The energies of the desired detail components are calculated and the normalized Euclidean distance of the energy differences between the three phases is used as a new fault detection criterion. The robustness of the proposed technique against the presence of rotor turn‐to‐turn faults and loading variations is demonstrated. In addition, an adaptive threshold level as a function of the voltage unbalance factor is proposed to guarantee the robustness of the diagnostic technique against unbalanced voltage sources. Experimental results demonstrate the effectiveness and sensitivity of the proposed diagnostic approach for the detection of stator faults in line‐connected and inverter‐fed motors. [ABSTRACT FROM AUTHOR]

An invasive diagnostic technique is proposed in this article for the detection and discrimination of turn-to-turn faults in the stator and rotor windings of synchronous machines during the startup period. For this purpose, search coils are installed in the machine to sense the rotational magnetic field along the air-gap circumference, while the difference in the related induced voltages (differential voltages) reveals its distortion, using it as a criterion for the detection of the faulty condition. Nevertheless, the rotor speed is a time-variant parameter, which changes from zero at the starting instant up to its rated value at a synchronous speed. Consequently, during the generator startup, the frequency of the induced voltages in the search coils needs to be updated continuously for obtaining reliable values for the differential voltages. A simple method is presented to achieve this goal by detecting the sequential zero crossing of the voltage waveforms. The proposed method is verified through simulation and experimental results. They show that the proposed diagnostic technique is capable of detecting and discriminating stator and rotor turn-to-turn faults during the machine startup period, both in generating and motoring conditions, with suitable accuracy and security. In addition, the region of stator turn-to-turn faults can be easily identified. [ABSTRACT FROM AUTHOR]

The impacts of the static synchronous compensator (STATCOM) on the traditional loss of excitation (LOE) protection are investigated in this article. To do a comprehensive study, a common and realistic excitation system is developed for the generator by employing the phase-domain model of the synchronous generator accessible in the real-time digital simulator. Using such a model, the LOE phenomenon is realistically studied in accordance with IEEE Standard C37. 102-2016, while the generator dynamics along with the LOE relay performance are investigated through different types of partial and complete LOE events. It is shown that in the presence of STATCOM, two major impacts on the generator and its LOE protection can be expected: 1) it imposes an additional time delay on the relay to detect the LOE failures, which depends on the generator initial loading and the type of LOE failure and 2) it might lead the generator to reach a new stable operating point without experiencing a loss of synchronism condition, during an improper changeover from automatic voltage regulator to manual voltage regulator operating mode. The related consequences for both of the impacts are discussed in this article, and some solutions are suggested to deal with the probable negative aspects. [ABSTRACT FROM AUTHOR]

A portable flux probe is proposed and investigated in this article to detect turn-to-turn fault in the rotor poles of the high rated salient pole synchronous machines. The rotor circuit is fed by a low amplitude sinusoidal voltage source with a fixed voltage amplitude which has a frequency more than a few hundred Hz to achieve the higher reaction of the shorted turns on the faulty pole, which results in a significant reduction of the magnetic flux in the air-gap. Numerous simulations and experimental tests are carried out to investigate the proposed probe and the related technique performance to specify the faulty pole versus the number of shorted turns, applied frequency and probable eccentricity in the rotor position. The obtained test results show that all stable turn to turn faults (weak or heavy ones) can be specified easily by applying a portable sinusoidal voltage source with the frequency in the range of more than a few hundred Hz. The experimental test results validate that the flux density can be reduced to about zero in the faulty pole face, even in the case of one shorted turn in the sample machine. [ABSTRACT FROM AUTHOR]

An efficient online flux‐based diagnostic approach is proposed to detect turn‐to‐turn faults in the stator and rotor windings of wound rotor induction machines, at an early stage of development, which can be applied in the online mode. Some flux sensors are installed in the stator slots to detect the rotational magnetic field at various positions along the air‐gap circumference. These sensors measure the flux linked to all winding coil groups, in the three phases. Any fault occurring either in the stator or rotor windings will disturb the air‐gap flux and create an asymmetry in the rotational magnetic field, which is detectable through the difference of the induced voltages in the corresponding flux sensors. The proposed diagnostic technique is evaluated by finite element analysis as well as by multiple experimental tests. The obtained results show that such invasive technique is able to detect and discriminate various faults in the stator and rotor windings with high accuracy, low calculation burden, proper sensitivity and appropriate robustness in the face of machine load level variations. [ABSTRACT FROM AUTHOR]

A new approach for generator loss of field (LOF) protection is proposed by estimating the field current based on the generator measurable parameters. The main idea of the proposed approach is that a significant difference will be created between the measured excitation and the estimated field currents during LOF occurrence. A differential index is introduced to monitor such difference and consequently to detect LOF failures. A detailed and realistic field circuit is considered for the generator by using the phase-domain model of the generator in the real-time digital simulator, while different types of LOF events can be simulated through such model as well. The obtained results show that the presented technique can detect various types of LOF events much faster than the conventional impedance-based scheme. Moreover, it exhibits more security than the conventional technique in the face of power system disturbances (e.g., stable power swing and out-of-step conditions). [ABSTRACT FROM AUTHOR]

A flux-based technique is proposed for the on-line detection, localization and discrimination of stator and rotor turn-to-turn faults in synchronous generators, using the measured air-gap rotational magnetic field. Simple magnetic field sensors (MFSs) are installed in the stator slots at different regions, and the corresponding induced voltages are measured. Several differential voltages are then obtained to give a picture of the rotational magnetic field symmetricity, whose distortions indicate the presence of the stator or rotor faults. The proposed diagnostic technique is presented in detail and validated initially by simulation results obtained with a finite element simulation package and afterwards through the experimental tests. The obtained results demonstrate that the proposed technique can be used to detect and discriminate stator and rotor turn-to-turn faults with appropriate sensitivity. In addition, the region of the stator turn-to-turn faults can be identified as well. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for the online detection of broken rotor bar(s) (BRBs) in induction motors, based on the analysis of the air-gap rotational magnetic field (RMF), being it indirectly sensed using the voltages induced in dual search coils installed in several stator regions. The induced voltages allow obtaining three differential voltages which reveal the symmetricity level of the mentioned field along the stator circumference. Under the presence of the broken bar(s), the RMF is disturbed by the rotor magneto-motive force, being these disturbances detected through the fundamental components of the differential voltages using a new time-domain analysis technique. The proposed diagnostic approach is verified by finite-element analysis and also by several experimental tests. A high sensitivity, robustness in the face of unbalanced voltage sources and motor load level variations are the main advantages of the proposed technique. Moreover, it is a secure method for BRB detection, easily implementable in low-cost digital signal processing units. [ABSTRACT FROM AUTHOR]

A real-time realistic framework for synchronous generator loss of field (LOF) protection studies is suggested in this paper by using the real-time digital simulator, which allows the user to realistically model the generator field supply circuit. By using such framework, the performance of LOF protection algorithms can be comprehensively evaluated in the face of the various LOF events including the short circuit and two types of the open circuit events, while the open circuit occurrence cannot be studied in the conventional simulation programs. The obtained results demonstrate that the generator dynamics are significantly different in the face of various LOF failures and then all of them must be regarded to develop the new LOF protection algorithms. By using the suggested framework, the performance of some recently proposed schemes along with the conventional impedance and the admittance relays are comprehensively evaluated. The obtained results from applying the various LOF failures show that, against the conventional relays, the new schemes cannot detect all types of LOF failures and so, they do not have enough reliability. [ABSTRACT FROM AUTHOR]

A new air-gap flux-based technique is proposed in this paper for turn-to-turn fault (TTF) detection and defective region identification, which is implemented in line-connected and inverter-fed induction motors. Some search coils (SCs) are used to measure the magnetic flux in various air-gap regions of the mentioned motor. The induced voltages in the SCs reveal the configuration of the rotational magnetic field (RMF) along the stator inner circumference to assess the symmetricity level of the flux distribution at each time instant. The RMF asymmetric distribution can be detected by comparing the induced voltages in various dual SCs (which under healthy conditions must sense identical magnetic flux) to detect TTFs and identify the faulty region as well. The proposed method is verified through finite element simulations and also by carrying out several experimental tests. Despite the fact that the proposed method is an invasive diagnostic technique, significant sensitivity and robustness in the face of unbalanced voltage sources and/or loading level are compelling evidence to use it for TTF detection at an incipient stage. The capability of the proposed technique to identify the faulty phase and the related region in the stator is another advantage of this invasive method, which cannot be ignored. [ABSTRACT FROM AUTHOR]

Power transformer, as one of the most important apparatus in power system, must be protected against the turn-to-turn faults. Although the various methods based on the terminal currents and/or voltages have been presented for transformer protection, the flux-based methods can be used to achieve the more accurate, sensitive, and secure results. Since the symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings, it can be considered as an appropriate criterion to achieve a suitable protection algorithm, which can detect the fault occurrence and identify the faulty phase/region. In this paper, a new leakage flux sensor is introduced and then a flux-based technique is proposed to detect and identify the faulty phase in transformers to apply in online conditions. By using the proposed technique, the faulty region can be identified in offline conditions, as well. The experimental results (which are done on a distribution transformer) show that this technique is secure in the face of overfluxing and transformer energizing conditions and can detect turn-to-turn faults with high sensitivity. Moreover, tap changer operation, imbalanced loads, and/or unsymmetrical voltage sources cannot influence the proposed technique security. [ABSTRACT FROM PUBLISHER]

Loss-of-field (LOF) phenomenon in synchronous generators may cause equipment damage and voltage drop in the power system, which can be terminated to a blackout. Conventional schemes, which detect LOF on the basis of the measured impedance from the generator terminal viewpoint, have some major drawbacks such as low speed, complicated setting procedure, and unsecure performance in the face of similar phenomena, e.g., stable power swing. In this paper, different electrical quantities of the generator including terminal voltage (V), current (I ), active (P) and reactive power (Q), and power angle (δ) variations are studied to achieve a secure technique for LOF protection in synchronous generators. Comprehensive studies show that a simple criterion based on polarities of V, Q, and δ variations is accessible to achieve this goal, which does not need a complicated procedure to set it. To evaluate the performance of the proposed algorithm, some cases are simulated on sample power systems under various operating conditions. Also, superiority of the proposed algorithm in comparison with the other schemes is proven by the obtained results, as well. Moreover, the proposed technique is experimentally tested by using some 2-kVA laboratory generators to detect LOF. [ABSTRACT FROM AUTHOR]

Among the various techniques for transformer protection, more accurate, sensitive, and secure results can be achieved by the flux-based ones. The symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings. So, it seems that this is an appropriate criterion to achieve a suitable protection algorithm, while it can be used to detect faults as well as identify the faulty phase/region. In this paper, a miniature sensor is proposed consisting of simple planar magnetic flux sub-sensors and located in the existing space between the transformer core and the first insulating layer to sense the leakage flux distribution. Comparing the induced voltages in symmetrical sub-sensors for each phase exhibits asymmetrical configuration of the leakage flux distribution and identifies the faulty region in that phase. Appropriate fine and tiny construction of the proposed sensors provides them a good choice to install in the transformer core vicinity. Then, the leakage flux can be sensed in the origin regions during turn-to-turn faults. Experimental results show that such sensors have high sensitivity to detect leakage flux that ejects from the core or comes back to it. [ABSTRACT FROM PUBLISHER]

Loss of field (LOF) phenomenon in synchronous generators may cause serious damages and voltage drop in the power system, which can result in a blackout. Conventional methods, which detect LOF on the basis of the measured impedance from terminal viewpoint, are slow and may exhibit mal‐operation in the face of other phenomena, e.g. stable power swing (SPS). In this paper, a novel technique is proposed to detect LOF in synchronous generators on the basis of some electrical quantities variations including voltage of terminal (V), current (I), active power (P), reactive power (Q) and power angle (δ). To evaluate the performance of the proposed algorithm, some cases are simulated under various operation conditions. Obtained results show that this algorithm on the basis of V, Q and δ not only can be considered as a fast LOF detector in comparison with the conventional impedance‐based schemes, but also it is a robust and secure technique in the face of SPS and other power system disturbances. The proposed algorithm is tested by using an experimental setup including the laboratory synchronous generators, too. The obtained results show that the proposed technique can exhibit suitable performance in the actual conditions. [ABSTRACT FROM AUTHOR]

Analyzing of detected partial discharge (PD) signals is a reliable technique to assess the electrical insulation in power transformers. In order to detect and locate the PD sources in power transformers, some distributed simple fine sensors are proposed and used, which are made by a few turns of thin enameled copper wire wrapped around the transformer core. They are distributed sensors, which sense PD voltage signals through capacitive coupling with the transformer windings. Two methods, including broadband and limited-band PD signal analyzing, are considered to identify defective phase and/or region on that phase through the proposed distributed sensors outputs. Transfer functions of these sensors are obtained and it is experimentally shown that although defective phase can be diagnosed, the expected priority to identify defective region is not regarded in broadband analysis, while a suitable limited frequency band can be found to achieve this aim. The idea is implemented on a sample transformer by injecting artificial PD signals to different high-voltage winding sections. The results show that not only PD signals can be detected through the mentioned sensors with high sensitivity, but also defective phase can be diagnosed using broadband analysis. Moreover, defective region can be accurately identified by limited-band analysis. [ABSTRACT FROM PUBLISHER]

Monitoring of partial discharge (PD) and its progress as the main cause of the insulation deterioration process in power transformers can encompass valuable information about the related insulation condition and reveals degradation mechanisms. In this study, some simple sensors, which are made from a few turns wrapped around the transformer core, are used to detect PD signals. Moreover, a feasibility study is done to identify defective phase/region based on the captured PD signals waveforms through these sensors. The idea is implemented on a 50 kVA, 20 kV/400 V three‐phase transformer by injecting artificial and quasi‐real PD signals to different sections of HV windings. Also, various transformer connections are considered in the experimental studies to find the effect of them on the waveforms of the captured signals (e.g. peak‐to‐peak value and signal energy). The obtained experimental results show that small PDs (as low as 10 pC) is detectable by the mentioned sensors and defective phase can be identified in all of transformer connection cases. Furthermore, considering failure to identify defective regions by broadband analysis, a limited‐band approach is proposed through obtaining |H(s)| for the sensors. The results show that exact defective phase/region identification is feasible by selecting a frequency band compatible with IEC60270 recommendation. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) is the most important factor in gradual insulation deterioration of high-voltage (HV) power equipment, and then PD trend monitoring is a great issue for their condition assessment. Impulsive high-frequency PD current/voltage signals can be detected by using electrical sensors, e.g. inductive/capacitive sensors. A comprehensive feasibility study is carried out to use the power frequency current transformers (CTs) that are already installed in medium voltage and HV electrical power systems instead of high-frequency CTs. To achieve this aim, frequency response of a sample protection CT is extracted experimentally and it is fitted to appropriate transfer functions to access the related frequency characteristics. Regarding improper CT frequency response and its extreme variations in different frequencies, reversed transfer function is obtained to apply to CT secondary signals for reconstructing CT input PD pulses. Two types of artificial PD pulses are examined to validate the proposed method and the experimental results show that power frequency CTs can be used for PD detection and measurement in some frequency bands. [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]

Current-transformer (CT) saturation phenomenon impacts the performance of the current-based protective relays and leads them to malfunction; so detecting and resolving such phenomenon are important issues in power system protection. This paper provides a modification for two well-established algorithms: 1) least square error and 2) artificial neural network to compensate and reconstruct CT's distorted secondary current waveform (CTDISCW). The effectiveness of an online algorithm is its operating capability in noisy environments and in the presence of travelling waves generated by any event. In addition, this algorithm must be stable against any normal variation in network structure. Then, both mentioned methods need to be modified to present proper results with an acceptable error in online conditions. In this paper, a real CT is considered to simulate, and a section of the Iranian power network is selected to generate CTDISCWs using the modeled CT, and to evaluate the proposed algorithms’ performance. [ABSTRACT FROM AUTHOR]

Internal turn‐to‐turn faults (TTF) are considered as a common cause of transformer failures. Such defects (especially minor TTFs) may result in minor changes in terminal currents/voltages as these are undetectable by conventional current and/or voltage‐based methods. In this study, a simple, sensitive and robust method is proposed to identify the TTF locations in power transformers by using core flux based technique. In this approach, a few turns must be wrapped around the transformer core legs to sense and detect the related core flux. Passing asymmetrical flux through a transformer core leg (due to a TTF) induces different voltages in the related sensors, which are located at different places. Variation of the core flux in the corresponding sensors indicates the faulty phase and the TTF location on that phase as well. The proposed technique is verified by some simulations and experimental tests. The obtained results show that the proposed technique successfully (i) detects all the TTFs, (ii) identifies the faulty phase, and (iii) specifies the faulty region on the related phase. Although the proposed method requires a few search coils to be installed on the transformer core legs, installing these thin wires will not change the transformer design significantly. [ABSTRACT FROM AUTHOR]

The CuII complex bis[hydroxybis(pyridin-2-yl)methanesulfonato-κ3 N, O, N′]copper(II) hexahydrate, [Cu(C11H9N2O4S)2]·6H2O, (I), crystallizes in the space group P, compared with P21/ c for the anhydrous CoII analogue bis[hydroxybis(pyridin-2-yl)methanesulfonato-κ3 N, O, N′]cobalt(II), [Co(C11H9N2O4S)2], (II). However, both molecules sit on a crystallographic inversion centre and are thus very similar in appearance. Jahn-Teller elongation of the Cu-O bonds [2.347 (3) Å in (I) and 2.064 (2) Å in (II)] influences the S-O bond lengths, which are all around 1.455 (3) Å in (I) and 1.436 (2)-1.473 (2) Å in (II). [ABSTRACT FROM AUTHOR]

In the title compound, C36H25F6O2P2+·I3−, hydrogen-bonded [{( p-FC6H4)3PO}2H]+ dimers assemble along the crystallographic c axis to form channels that house extended chains of triiodide anions. Although the I-I bond lengths of 2.9452 (14) and 2.9023 (15) Å are typical, the inter-ion I...I distance of 3.5774 (10) Å is unusually short. A posteriori modelling of nonmerohedral twinning about (100) has been only partially successful, achieving a reduction in the maximum residual electron density from 5.28 to 3.24 e Å−3. The inclusion of two low-occupancy I-atom sites (total 1.7%), which can be interpreted as translational disorder of the triiodide anions along the channels, reduced the maximum residual electron density to 2.03 e Å−3. The minor fractional contribution volume of the nonmerohedral twin domains refined to 0.24 and simultaneous refinement of the inversion twin domains showed the crystal to be a 0.5:0.5 inversion twin. [ABSTRACT FROM AUTHOR]

The article discusses a study on Bis(methyltri-o-tolylphosphonium)octaiodide. Researchers reacted equimolar amounts of tri-o-tolyphosphine and methyl iodide at room temperature in dry dichloromethane and then 25 milliliters (ml) of anhydrous dichloromethane was added. The study showed that the octaiodide bonding distances are indicative of a di-iodide molecule and two tri-iodide anions.

The Cu(II) complex bis[hydroxybis(pyridin-2-yl)methanesulfonato-κ(3)N,O,N']copper(II) hexahydrate, [Cu(C(11)H(9)N(2)O(4)S)(2)]·6H(2)O, (I), crystallizes in the space group P1, compared with P2(1)/c for the anhydrous Co(II) analogue bis[hydroxybis(pyridin-2-yl)methanesulfonato-κ(3)N,O,N']cobalt(II), [Co(C(11)H(9)N(2)O(4)S)(2)], (II). However, both molecules sit on a crystallographic inversion centre and are thus very similar in appearance. Jahn-Teller elongation of the Cu-O bonds [2.347 (3) Å in (I) and 2.064 (2) Å in (II)] influences the S-O bond lengths, which are all around 1.455 (3) Å in (I) and 1.436 (2)-1.473 (2) Å in (II).