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In order to protect the transmission lines against lightning strikes, it is important to investigate the tower grounding system. In this paper, a recent method called hybrid continuous circuit-trapezoidal integration method is used to calculate the impulse impedance of the grounding system. Moreover, conventional structures of the grounding systems have been simulated and the results show that, with the same wire length, the square with additional wire system has the least impulse impedance as compared to counterpoise, square and crow’s foot. Moreover, the effects of soil resistivity and lightning current rise-time on the impulse impedance of these grounding systems are investigated. It is concluded that the design of the grounding system depends on the geographic location of the site in terms of soil resistivity and isotropic characteristics of the area in terms of lightning current rise-time.

Eccentricity fault in double-sided axial flux permanent magnet generator is very difficult to be detected as the fault generated variations in terminal electrical parameters are very weak and chaotic, especially at the initial stages of the fault occurrence. In addition, one of the most important problems in any fault diagnosis approach is the investigation of load and speed variation on the proposed indices. To overcome the aforementioned difficulty and problems, this paper adopts a novelty detection algorithm based on Hilbert-Huang transform (HHT) which is a timefrequency signal analysis approach based on empirical mode decomposition and the Hilbert transform. It is well suited for reliable fault diagnosis since it is unaffected by transient conditions which make the diagnosis process incur into false alarms. The HHT-based methods has been demonstrated in recent years for rotor and bearing faults detection of induction machine and also for stator faults identification in PM synchronous machines with radial flux structure. This study explores the possibility of applying the technique to the detection of dynamic eccentricity faults in double-rotor double-sided stator structure axial flux permanent magnet generator under variable load and speed conditions. This approach relies on two steps: estimating the intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD) and computing the instantaneous amplitude (IA) and instantaneous frequency (IF) of IMFs using the Hilbert transform. The more significant IMFs are determined by means of Hilbert spectrum, which is applied for accurate eccentricity fault diagnosis. The eccentricity severity can be evaluated based on the IMFs energy value. The theoretical basis of the proposed method is presented. The effectiveness of the proposed method is verified by a series of simulation and experimental tests under different conditions. The results show that the presented approach in this paper is robust against load and speed variations. [ABSTRACT FROM AUTHOR]

In the power grid, various conditions may occur that saturate the core of a current transformer. Saturation of the protection core of the current transformers can cause a malfunction in the protection relays. To prevent malfunction of the protection relays caused by the current transformer saturation, software and hardware methods can be used. In the software method changes in the protection relay algorithm are used. In the hardware method special devices are used. A new hardware method is presented here, which uses compensation to prevent the occurrence of current transformer saturation. In the proposed method, compensation is done by controlling an applied voltage to the current transformer secondary terminals using negative resistance. The proposed method, despite its simplicity and cost‐effectiveness, has good performance in preventing saturation in various conditions. The high reliability in terms of the risk of secondary open circuit and its application in various saturation conditions, even in the case of severe saturation are the main advantages of the proposed method. Also, the proposed method does not produce distortion in the transformation of high‐order harmonics by the current transformer. To verify the effectiveness of the proposed method, prototype design and construction have been performed. The simulation and experimental results of laboratory tests have been presented and analysed. [ABSTRACT FROM AUTHOR]

In some conditions, the flux in the core of current transformers (CT) increases. If this increase in flux leads to saturation of the protective core, it can create a lot of problems in power system protection. One of the hardware solutions to prevent the occurrence of core saturation in CT is the fixed switched resistor demagnetization method. Due to disadvantages such as dependence on CT parameters and inefficiencies in severe core saturation, the use of this method has not been expanded. This paper proposes a new method to improve the fixed switched resistor demagnetization method. In the proposed method, instead of using a fixed resistor in the circuit topology, an adjustable resistor with an auxiliary transformer is used. In the previous method, the control process is based on flux estimation from the secondary terminal voltage. The control process in the proposed method is based on the second derivative of CT secondary current. To verify the effectiveness of the suggested method, first simulation is done using COMSOL and MATLAB softwares and then all necessary electronic and control circuitry are designed and built. Experimental test is carried out on a 20 kV- 500/5 A CT. The simulation and experimental results show that this method prevents the CT from saturation in case of short circuit faults. The main advantages of this method are independent to CT parameters and efficient in severe core saturation. [ABSTRACT FROM AUTHOR]

The magnetic effects and consequently the radial force are the main causes of noise in switched reluctance motors (SRMs). In this study a new design for SRM is developed in order to reduce acoustic noise. In this research a new design for SRM is developed in order to reduce the acoustic noise. In this investigation, at first, different SRM structures are simulated using JMAG software. An 8/6‐pole SRM is designed and built with special modification in the rotor and stator structures. For increasing mechanical strength, trapezoidal stator and rotor pole shape with poles arc βr = βs = 21° are proposed. In this design the taper angles of stator and rotor poles are equal. For noise reduction, the mechanical restructuring is done according to stress analysis. The new designed SRM are simulated and tested experimentally under no‐load and full‐load conditions. The results are shown and compared. Comparison between these results and the results of other structures shows that the acoustic noise of the newly designed motor is reduced considerably. The results show an acoustic noise reduction of ∼72% in new structure SRM. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive sliding mode type‐2 neuro‐fuzzy control scheme for power‐control and speed‐control modes of doubly fed induction generator (DFIG). DFIG‐based wind turbine system operates as variable‐speed wind energy conversion system (WECS) with constant frequency. In the proposed controller design, a sliding mode control (SMC) strategy is used for online training of the parameters of type‐2 fuzzy set (T2FS) membership functions. Due to the uncertainty of the wind speed and variation in parameters in the WECS, an interval T2FS is used in the proposed control scheme. Based on the controller inputs, the SMC adaptive strategy is used to tune the parameters of antecedent and consequent parts of T2FS. These inputs are active and reactive power and rotor speed errors and their time derivative. These inputs fed to the type‐2 neuro‐fuzzy system. The results of simulation for a 1.5 MW DFIG‐based WECS are compared with the classical proportional–integral (PI) controller and type‐1 neuro‐fuzzy controller to validate the effectiveness of the proposed controller in power‐control and speed‐control regions. The results of simulation indicate that, in comparison to the PI and type‐1 neuro‐fuzzy controller, the proposed control scheme has better performance in both power‐control and speed‐control modes. [ABSTRACT FROM AUTHOR]

An essential requirement to improve the lightning performance of transmission line is the achievement of low impulse impedance of grounding system, which diminishes the occurrence of the external overvoltages. In this study, for the first time, a multi‐cross structure used as transmission line tower‐footing grounding system is investigated by means of hybrid continuous circuit‐trapezoidal integration method (HCCTIM). It is discovered that the angle of minimum impulse impedance or the optimal structure of multi‐cross grounding system is mainly dependent on the branch length compared to the effective length of a single horizontal conductor. Furthermore, in the current work, the trapezoidal integration method is used to solve the continuous circuit equations which elements are extracted from electromagnetic integral method, called HCCTIM. Coupling elements and soil ionisation are considered in this model. This method is an accurate, simple, and less time‐consuming computational method. The comparison of the results with measurements, other recent simulations and CDEGS software, satisfactorily validate the proposed method. [ABSTRACT FROM AUTHOR]

This study presents an adaptive sliding mode type‐2 neuro‐fuzzy controller for power control of doubly fed induction generators (DFIGs). DFIG‐based wind turbine system is variable‐speed constant‐frequency wind energy conversion system. In this proposed control scheme, in order to enhance its performance, sliding mode control (SMC) theory is used for online training the parameters of type‐2 fuzzy system membership functions. To regulate the antecedent and consequent part parameters, the SMC adaptive technique is used according to the controller inputs. These inputs are active and reactive power errors and their time derivative, which applied to the structure of T2NF system. The proposed controller employs an interval type‐2 fuzzy system because of the uncertainties of the wind speed and variation in parameters in the wind power conversion system. The simulations carried out for a DFIG‐based 1.5 MW wind turbine. The results of simulation are compared with the classical proportional–integral controller to confirm the effectiveness of this control scheme. This comparison is carried out between the cut‐in and rated region wind speeds. The results of simulation show that the proposed control scheme has better performance to track the peak power and is more robust to machine parameter variations. [ABSTRACT FROM AUTHOR]

The loss of excitation (LOE) is one of the main faults of the synchronous generator, which may cause serious damages to generator and makes the power system unstable. The main problem to distinguish between LOE and stable power swing (SPS) is a time delay, which is a main part of the detection time in all recent protection methods. This study presents a new method for LOE detection in the synchronous generator, which reduces time delay by half. The proposed method exploits a new index which is based on the variation of the generator output reactive power. It is a combination of the first- and secondorder derivative of the generator output reactive power. In this method, after the generator losses its excitation, the proposed index will become and remain negative for a while. To prevent mal-operating under slowest power swing condition, the time delay of 0.85 s is used. The performance of the proposed method is evaluated under different conditions. The simulation results and experimental tests confirm the accuracy and fast operation of the proposed method. [ABSTRACT FROM AUTHOR]

Here, based on wide‐area measurement systems (WAMS), an adaptive tripping index (TI) is proposed for online prediction of tripping signals with respect to wide‐area out‐of‐step (WAOOS) protection of synchronous generators. The proposed TI included two different equations consisting of a straight line for unstable inter‐area oscillations and a sinusoidal line for WAOOS transient instability. For online identification of coherent generators with respect to inter‐area oscillations, based on evaluating the correlation coefficients between generator behaviours, an index is proposed from which the global tripping signals (GTS) are calculated. The GTS consist of the rate of change of inter‐area rotor angle oscillation between two oscillating areas in the centre of inertia frame. Actually, the proposed scheme is an adaptive and online index from which the critical inter‐area angle is adjusted individually by evaluating GTS at each sampling time gathered from the WAMS data. The proposed strategy is implemented on an IEEE 39‐bus test system and its performance is investigated by simulating typical scenarios during time‐domain simulations. The results show the effectiveness of the proposed scheme for fast prediction of WAOOS protection in real‐time environment. [ABSTRACT FROM AUTHOR]

In engineering terms, it is always desirable to maximise the efficiency of the motor and to look the problem in economic viewpoint, minimisation of the weight and cost of the motor is required. As these two aspects are like two sides of a coin, it is usually aimed to acquire the best efficiency per weight and cost. As a result, the performance improvement of permanent‐magnet synchronous motor (PMSM) has two sides: technical and economic. This study proposes a new approach for design optimisation of an interior PMSM (IPMSM) taking into account both technical performances and economic considerations. The selected rotor configuration is a good candidate for general purpose industrial applications. A multi‐objective optimisation technique based on a new and efficient magnetic equivalent circuit of the motor is applied to obtain optimal motor parameters. A Pareto front composed of possible optimal solutions is provided. The best optimal solution is then selected using a k‐means clustering algorithm. To verify the efficacy of the design optimisation, the performance characteristics of the optimal PMSM are compared by both the finite element simulations and the experiments. In the test setup, an 8‐pole, 200‐Watt, four‐phase IPMSM with an optimised structure is prototyped where the results give agreeable accuracy. [ABSTRACT FROM AUTHOR]

In conventional methods, distributing and chording the winding of a motor can be used for controlling the harmonic contents of magnetomotive force (MMF). This solution may not be able to reduce the harmonic contents of motors to the desirable value that may cause unsuitable performance of the motor such as crawling phenomenon. Moreover, the harmonic contents of the MMF cause increase of the losses and reduction in efficiency of electrical motors. The effect of the new winding scheme was investigated to improve the induction motor operation by reducing the harmonic contents of the MMF. By applying the new winding pattern in an induction motor, the harmonic component groups of fifth (5, 11, etc.) and seventh (7, 13, etc.) were reduced considerably. A simulation approach alongside experimental results derived from a two‐pole, 400 V, 50 Hz, 200 W, three‐phase induction motor validate the improvement operation of the motor. [ABSTRACT FROM AUTHOR]

Integration of wind resources into the power systems has increased the technical and financial concerns in transmission expansion planning. In this paper, a stochastic structure is demonstrated for transmission expansion planning with allocation of fixed series compensation under wind and load uncertainties. Fixed series compensations have the ability to increase the transfer capacity of transmission lines. However, their significance benefit for transmission expansion planning is their higher effectiveness in power dispatching, which results in lower investment costs, compared with planning without fixed series compensations. The proposed planning model simultaneously optimizes targets such as the investment cost, the congestion cost, and the expected energy not supplied in each stage. The presented planning model is a complicated nonlinear optimizing problem. For introducing group of nondominated optimal solutions, multi-objective gray wolf optimizer algorithm based on probabilistic optimal power flow is used. Then, fuzzy approach is used to lead to the best response. For demonstrating the feasibility and susceptibilities of the proposed algorithm, the planning methodology has been illustrated on the IEEE 24-bus and Colombian test systems. The results acquired from the simulations monitor capability of the proposed structure in order to satisfy various planning indices. [ABSTRACT FROM AUTHOR]

Sinusoidal voltage waveform in synchronous generators is of great significance in power systems. Generally speaking, the output voltage of a synchronous generator is semi‐sinusoidal including some disturbance frequencies (known as harmonics) rather than the fundamental frequency. The harmonic contents cause them to increase in iron loss and reduction in efficiency of electrical machines. For this reason, the harmonic contents of synchronous generators should be carefully taken into consideration. In this study, a new winding pattern for stator of the synchronous generators is proposed to eliminate the harmonic contents of output voltage and so makes it more sinusoidal. In this method, the harmonic contents of output voltage are almost eliminated by selecting the optimal number of conductors per slot. Afterward, through several analytical and simulation studies the suggested winding pattern is compared with those of conventional ones. Moreover, the experimental setup is carried out based on a 3 kW, 1500 RPM synchronous generator. The conventional and proposed winding patterns are separately tested in this setup, and then the harmonic‐based behaviour of output voltage is studied for each case under different load conditions. The obtained results prove the superiority of the proposed winding pattern over the conventional patterns. [ABSTRACT FROM AUTHOR]

In this paper, a new active method for power factor correction (PFC) is presented and applied to a single-stage AC/DC flyback converter to reduce the total harmonic distortion of the input current, achieve better power factor compensation, and improve converter reliability. The proposed circuit consists of a low-power portable dual-purpose inverter that can work in 2 main modes. In the normal mode of converter operation, the PFC circuit operates as an active harmonic filter compensator. In the second mode, which occurs in converter outage conditions, the inverter behaves as a sinusoidal backup voltage power supply for the converter by using a backup battery and the SPWM control method. In this technique, the main switch of the converter operates in borderline conduction mode, but the RMS input current as well as peak and ripple currents are reduced significantly. Simulation analysis and experimental results are presented. [ABSTRACT FROM AUTHOR]

In helical flux compression generators, the ohmic and intrinsic flux losses limit severely the performance of them. One of the sources of intrinsic flux losses is the turn skipping flux loss. This paper first introduces an accurate criterion for the prevention of the turn skipping phenomenon in these generators. Then, a novel method is presented to calculate the flux loss due to this phenomenon. In addition, an equivalent resistance is introduced to consider the effect of turn skipping flux loss on the generator performance. The calculation results show that, as soon as the turn skipping occurs, about 30% of a turn flux is lost and this value is increased rapidly with eccentricity increasing. Therefore, it is necessary to prevent this phenomenon as far as possible. The calculated output current of the simulated generator also shows that the maximum current when considering the turn skipping loss is about 15% of the maximum current in the case of ignoring it. Based on the authors' knowledge, quantification of the turn skipping flux losses has not been presented previously in the open literature. [ABSTRACT FROM PUBLISHER]

This paper presents a multiobjective optimal design of the parameters of surface‐mounted permanent magnet synchronous motors (PMSMs) considering saturation of the iron core. Multiobjective parameter tuning can further improve the performance characteristics of such motors. Specifically, efficiency and total volume are of great importance in industrial applications. A new formulation is presented for these two objective functions. In this paper, a multiobjective optimization based on a modified nondominated sorting genetic algorithm II (NSGA‐II) is utilized for optimal design of PMSM. Pareto‐optimal solution is achieved, and optimal variables are obtained. The best solutions are then selected by k‐means clustering algorithm for the motor under study. Finally, finite element analysis (FEA) is performed to validate the optimization procedure. The FEA results agree well with the values obtained by the optimization process. [ABSTRACT FROM AUTHOR]

Summary: The uncertainties caused by restructuring in power systems make transmission investment less attractive for the private investors and increase the risk level. In this paper, a merchant‐based stochastic method is presented for multi‐year transmission expansion planning from the viewpoint of private investors with allocation of fixed series compensation under wind, bids of generators, and load uncertainties. This proposed method maximizes absorption of private investment and eliminates monopolies in restructured environments. The grey wolf optimizer algorithm and point estimation method are applied as the optimization tool and for management of the uncertainties, respectively. In order to demonstrate the dependability of the proposed approach, the planning methodology has been illustrated on the IEEE 24‐bus and 118‐bus test systems. The results of this research show that adding fixed series compensation, besides the reduction of investment cost, will provide a good vision for private investors in order to get suitable transmission projects for investing. [ABSTRACT FROM AUTHOR]

Summary This paper presents an adaptive scheme for predicting out‐of‐step (OOS) condition of synchronous generator based on the Bayesian technique. The proposed scheme performs as an intelligent OOS method for synchronous generators from which by using training variables, the tripping signals are estimated. For classifying target classes between stable and OOS conditions, a series of measurements are derived under various fault scenarios including topological and operational disturbances. The tripping signals are estimated by using feature selection technique based on the Bayesian technique. In this procedure, the data of input variables and corresponding output target classes are implemented as input‐output pair data for Bayesian training and testing. For this propose, the ability of the OOS protective scheme is examined for a number of unseen samples in working mode. The proposed approach is applied on IEEE 39‐bus test system from which by using trained variables, the tripping signals are estimated online. Furthermore, to evaluate the proposed protective scheme in real‐time environment, a 2‐machine experimental case is used to assess the effectiveness of the proposed scheme. The results show a promising performance of proposed protective scheme for proper estimating of tripping signals. [ABSTRACT FROM AUTHOR]