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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]

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 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]

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]

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]

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).