The protection of transmission and sub-transmission lines is conducted by overcurrent, line differential and distance protections among which the use of distance protection is very common.Mal-operation of protection equipment, including distance protection, can occur due to improper choose of the setting. This paper presents the proper method for calculation of the phase-to-phase loop resistance reach of distance protection with Quad characteristic and the impedance starter at the sub-transmission level to prevent mal-operation of the distance relay when processing its algorithm. In this work, based on the practical experiences on several industrial distance relays, it is shown that there is a possibility of improper detection of the fault loop by distance protection and then improper relay operation for out of zone faults. After review of the subject, and expressing the mathematical relations governing the problem, the appropriate phase-to-phase loop resistance reach determination method is put forward. Finally, using the information obtained from a practical incident, the efficiency of the proposed method is verified.

Rational function-based models have proved to be very efficient for accurate frequency-dependent modeling of power system components. These models are able to characterize the components terminal behaviours (analysing the admittance matrix) for nodal analysis. This provides a fast convergence and inherent stability to the solution routine of the model. This work presents a general framework for interfacing the dynamic phasor method to the rational models. That would be promising for the electromagnetic transient analysis (under harmonic distortion), in the frequency domain. Therefore, Y-element rational pole-residue models (employing the vector fitting method) are developed. Moreover, the pole-residue model is converted into the state-space representation. Next, the dynamic harmonic approach (in the frequency domain) is employed for harmonic analysis. It is shown that the order of state-space system can become a major concern for frequency-dependent networks analysis. Therefore, to generate a reduced-order model, the balanced realization theory is applied. Moreover, (for the sake of simplicity and efficiency) the trapezoidal integration rule is employed to discretise the state-space equations. For validation of the modelling, it is applied on three test case studies and results of these studies are compared with their time-domain analysis results.

Inappropriate design of transmission line towers in areas with high lightning density increases the outage rate of the line due to direct lightning strikes. In this paper, The lightning activities of areas covered by western regional electricity company during five recent years were collected from weather stations. Based on collected datasets, the Isokeraunic level and the lightning density of different areas have been computed. This information were further used to investigate and predict the outage rate of double circuit 230 kV transmission lines with one shield wire (existing plan) due to direct lightning strikes. Due to high density of lightning activities in some areas, the calculation results show high outage rate in these areas, which has been confirmed by actual experiences. In order to overcome this problem, a tower design with two shield wires was proposed for new developments. The outage rate of the transmission line with the two shield wire design with extracted lightning densities were compared with the existing tower installed. The results show high degree of improvement in outage rates. In order to modify the existing transmission line outage rates, installation of surge arresters and their capabilities were studied. Due to statistic nature of lightning, Monte Carlo method along with EMTP simulations were used in investigations. Simulations results show placement of surge arresters on two upper phases can reduce the shielding failure outage rates in the transmission line, significantly. The pros and cons of surge arrester installations in transmission line to compensate inappropriate tower design are discussed. Results of this study can be used for further transmission line developments in these areas.

This study presents a generalised representation of voltage source converter (VSC) based high voltage direct current (HVDC) systems appropriate for power flow studies using the Newton-Raphson method. To reach this aim, the active loads and ideal synchronous machines are employed in order to incorporate both converter losses and power balance, respectively. Also, considering different aspects of computer implementation, the proposed solution method uses the conventional Newton-Raphson method. The proposed representation considers practical restrictions, switching and conduction losses of semiconductors, and different control strategies for VSC-HVDC stations. Moreover, the proposed generalised representation of VSC-HVDC systems can be easily extended to incorporate the multi-terminal VSC-HVDC grids in an efficient manner. To investigate the application of the proposed representation for VSC-HVDC systems and load flow solution, three test systems including the standard IEEE 30 bus and IEEE two area RTS-96 networks are used and discussion on results is provided. Results show that the proposed algorithm is able to solve AC-DC power flow problems very efficiently with considerably less time in comparison to other existing algorithms.

Here, using the probabilistic evaluation based on the Monte Carlo method, back-flashover rate and shielding failure flashover rate of 230 kV overhead transmission lines in the western regions of Iran are evaluated. To such an aim, first, the number of thunderstorm days per year is collected from the reported weather information in order to determine the ground flash density. Then, using MRU-200 equipment, the tower-footing resistance of several towers is measured. Matlab® software is used in order to produce lightning surges considering its probabilistic nature and randomly distribution on the ground to evaluate striking distance based on the geometric model. Then, calculated parameters are transferred to EMTP-RV software by establishing a link to perform the transient simulation and report the results for modelled 230 kV transmission line. Finally, considering IEEE-1243 standard, it is shown that due to high ground flash density, using 230 kV tower with one shield wire is not sufficient to protect the line against lightning phenomena.

This study presents design and analysis of a pulse capacitor charge power supply (CCPS) system by employing a novel brushless field assisted induction generator (BFAIG). Unlike the conventional induction generators, in the proposed configuration of this study, in addition to the phase windings, the stator utilises an assisted DC field coil, which is responsible for production of controllable flux inside the machine. As the main salient feature of including the DC field coil which increases controllability of the flux, providing a regulated terminal voltage in a very wide range appropriate for CCPS applications can be pointed out. In addition, due to the lack of brush and winding on the rotor in the proposed BFAIG, stability, long life and high reliability can be addressed as appropriate characteristics of this structure. Moreover, in this study, analytical design of the proposed BFAIG is presented and two-dimensional magnetic-field distribution is performed by using MagNet CAD package to verify the design procedure. On the basis of obtained results from electromagnetic-field analysis, a CCPS is simulated and studied. The simulation results confirm the performance and efficiency of the presented CCPS.

In this study, by using the electromagnetic field analysis, the design of brushless DC generator with a novel construction and controller, appropriate for variable speed applications, is proposed. In the proposed machine, unlike the conventional structure, an assisted DC field coil is employed instead of permanent magnet excitation to provide a regulated voltage. Results of the electromagnetic field analysis show that including the DC field coil increases the controllability of the flux in different machine parts which provide a regulated terminal voltage in a wide speed range appropriate for variable speed applications. Moreover, the maximum power point tracking is achieved by controlling the DC field current along with producing optimal turn-on and turn-off angles for stator winding using the electromagnetic analysis based on optimal finite element analysis. Also, an appropriate controller is designed to control the DC field coil current. To verify the actual performance of the proposed configuration, a 1.5 Kw machine is manufactured and tested followed by the discussion on results. The obtained experimental results are in good agreement with the results of the electromagnetic analysis which confirm the maximum power trackability and robust output voltage regulation of the proposed conversion system under different shaft speeds and load conditions.

This study proposes a generalised STATCOM model employing active load and ideal synchronous condenser representation and its related power flow solution. The proposed method considers the effects of DC side voltage, internal switching losses, and operation mode on the power flow problem. To such aim, the proposed model tackles with a tap changing transformer accompanied by a variable conductance at the DC side in order to model the switching losses. This model can also take into account voltage regulation, reactive power control as well as amplitude modulation ratio and practical limitations. It is worth noting that the proposed model can be easily used for power flow studies by applying ordinary changes to the prevalent Newton–Raphson-based power flow methods. The introduced model is applied to two test systems including IEEE 14-Bus system, followed by a discussion on results.

The phase-shifting property has been formulated in the dynamic harmonic domain in a recently published paper. The main idea is to apply a phase-shifting matrix to the output when phase-shifting the inputs by an angle α. This letter demonstrates that the phase-shifting property has to be reformulated when applied to time-periodic systems involving switching functions. The proposed reformulated property assumes proper commutation of the phase-shifting matrix and achieves zero error regardless the periodic system under study.

In this paper, a general representation of multi terminal VSC-HVDC based microgrids appropriate for power flow studies using Newton-Raphson method is developed and presented. To such aim, active loads and ideal synchronous machines are employed in order to incorporate both converter losses and power balance, respectively. The proposed representation takes into account the practical limitations, switching and conduction losses of semiconductors and the different VSC-HVDC stations control strategies. Moreover, the proposed generalized representation of VSC-HVDC systems can be easily extended to incorporate multi terminal VSC-HVDC based microgrids in an efficient manner. The proposed representation for VSC-HVDC systems and load flow solution are applied to a test system, followed by discussion on results of written computer program. Results show the proposed algorithm is able to solve ac/dc power flow problems with considerable less time in comparison to other existing algorithms. Developed presentation for multi-terminal VSC-HVDC can be effectively applied to power flow solution of AC and DC microgrids.

This paper presents the principles of operation, electromagnetic behavior analysis, and a search technique based on the finite-element analysis in order to determine the optimum control parameters of an improved flux path Homopolar brushless dc motor (IFP-HBLDC). In the proposed IFP-HBLDC structure, a permanent magnet is replaced by a dc excited assisted field coil to control and regulate the flux. In this paper, for different values of speed, maximum torque is determined by calculating the optimal turn-on and turn-off angles and the optimal field current which provides more flexible control over wide ranges of speed. To such aim, the behavior of the commutation angles is analyzed first by a numerical technique using the 3-D electromagnetic field analysis, in which the analysis of the collected data has shown that the commutation angles providing the maximum electromagnetic torque. The technique was successfully used offline to determine the optimum firing angles for achieving the highest drive efficiency to maximize the electromagnetic torque in a prototype 1.5-kW three-phase IFP-HBLDC motor drive intended for variable speed application. The performance prediction and test results are found in good correlation.

In this paper, a frequency-based analytical approach for dynamic analyzing of unbalanced three-phase systems in the presence of harmonic distortion using sequence domain is put forward. As will be shown, classical symmetrical components proposed by Fortescue is not applicable under nonsinusoidal periodic condition. In such cases, generalized symmetrical components proposed by Tenti et al. can be used to calculate sequences from phase domain values. However, it introduces a new sequence component called residual component, which has a different value for each phase and cannot be directly obtained based on sequence networks. To such aim, using dynamic harmonic domain, an approach that makes it possible to use features of classical symmetrical components and modify the outputs to compute sequences based on the concept of generalized symmetrical components is proposed. Moreover, it is shown that using equivalent circuit for triplen harmonics is essential to find a relation between residual components since if sequences are connected in parallel, it is not possible to modify results of classical symmetrical components and this equivalent circuit should he directly analyzed. Time domain software is used to perform conventional lumped circuit simulation and validate the time domain responses resulted from DHD.

In this paper, analysis of an improved axially flux path brushless-dc machine (IAFP-BLDM) with the enhanced housing including its operation principle and particular structure is presented. The proposed configuration efficiently improves the magnetic performance by reducing the reluctance and leakage flux. Moreover, unlike the conventional brushless-dc generators, the proposed configuration of this paper utilizes an assisted dc field coil replaced with the permanent-magnet excitation. As the main salient feature of including the dc field coil which increases the controllability of the flux, providing a regulated terminal voltage in a very wide range appropriate for variable speed applications can be addressed. In this paper, by employing the finite-element method, the 3-D magnetic field analysis of the IAFP-BLDM is carried out by using the MagNet CAD package (Infolytica Corporation Ltd.). In order to verify the actual performance of the proposed configuration, a 1.5 kW, 3600 rpm, 9-6 salient poles and two layers are manufactured and tested followed by a discussion on the results. The output results were in good agreement with the analysis results, and also the output performance was verified by the experiment set.

In this paper, a frequency-based analytical approach is presented for dynamic analysis of three-phase balanced systems in the presence of harmonic distortion based on single-phase analysis. By providing mathematical foundation, this study proves that a three-phase balanced system (linear or non-linear, supplied by periodic balanced sinusoidal or non-sinusoidal sources) is completely balanced during both transient and steady-state conditions. This is done by utilizing Dynamic Harmonic Domain (DHD) and defining a phase-shift matrix in frequency domain. As the most noteworthy application of the proposed methodology, single-phase modeling approach is put forward. Therefore, during the transient period, one can analyze only one phase of a three-phase balanced system and calculate exact quantities of the other phases without performing extra simulations, which is not possible through time domain. The introduced concept has been applied to different test cases including three-phase transformer inrush current. In addition, the proposed approach has been utilized to obtain a single-phase model of VSC-based power electronic devices for dynamic harmonic analysis, followed by discussion on results.

Harmonics have become an important issue in modern power systems. The widespread penetration of non-linear loads to emerging power systems has turned power quality analysis into an important operation issue under both steady state and transient conditions. This paper employs a Dynamic Harmonic Domain (DHD) based framework for dynamic harmonic analysis of VSC-HVDC systems. These systems are widely used in modern power systems in both distribution and transmission levels in order to provide voltage profile improvement, power flow control and power loss reduction. In this paper, appropriate modeling of VSC-HVDC systems for harmonic propagation is performed by means of switching function which provides a connection between DC and AC sides. Also in this paper, dynamics related to DC side capacitor are taken into account which can greatly affect the transient response. In order to validate the results, the proposed method has been successfully tested on a test system and the obtained results are compared to those of a time-domain software, followed by discussion on results.

Harmonics have become an important issue in modern power systems. The widespread penetration of non-linear loads to emerging power systems has turned power quality analysis into an important operation issue under both steady state and transient conditions. This paper employs an Extended Harmonic Domain (EHD) based framework for dynamic analysis of long term analysis over voltages during the transients caused by inrush currents while large power factor capacitors are located at transformer secondary side. In such cases, a combination of capacitor and inductive system impedance may lead to parallel resonance circuits of high impedance. As a significance of the developed method, it is fully frequency domain dependent solution technique which uses time dependent Fourier series, orthogonal bases and matrix operators as addressed in EHD. The proposed method has been successfully tested on several networks and the obtained results are compared to those of a time-domain software, followed by discussion on results.

This study presents a novel methodology for steady and dynamic states harmonic analysis of power systems. It employs a decomposition framework so that harmonic-producing devices are considered as separate subsystems which are solved via the extended harmonic domain (EHD) technique. The EHD is inherently a frequency domain dependent solution method that provides dynamic harmonic indices based on operational matrices. The remaining system is modelled and resolved via commonly used harmonic analysis methods while transient stability (TS) is conducted (at fundamental frequency) to account for dynamic behaviour of generators and controllers. Interfacing of EHD and TS solutions is performed via an iterative scheme. As for steady-state initialisation, an efficient and robust algorithm is proposed in this study. The proposed method is implemented in an existing software package and applied to IEEE 9-bus test system. A thorough comparison of the proposed method with the PSCAD/EMTDC software tool is also presented.

It is well known that energizing a transformer can cause significant transients and harmonic pollution especially in the first few cycles. The waveforms of the 3-phase inrush currents are different even if the transformer is operating in a balanced condition; but analyzing the harmonics of 3-phase inrush currents shows that they are completely balanced if the transformer is under a balanced condition. This observation is possible only if the transformer is analyzed by using the dynamic harmonic domain. The dynamic harmonic domain provides dynamic analysis of the harmonics in the transformer from transient period to steady state. In this paper, physical meaning of harmonics during the transient period is also included. Moreover, a concept of 3-phase balanced systems under dynamic nonsinusoidal conditions is presented and explained with the inrush current in a 3-phase transformer.

In this paper, a novel analytical approach is put forward which leads to phase-shifting property of harmonics in a periodic system. Based on the illustrations, it is shown that if all of the input sources of the periodic system are shifted by $\boldsymbol{\alpha }$, the entire outputs will be shifted by $\boldsymbol{\alpha }$ as well in both transient and steady states. There is no limitation for such a system as it can be either single or three phase, linear or nonlinear, or supplied by periodic balanced or unbalanced sinusoidal/nonsinusoidal sources. According to this concept, the source angle affects only the phase angle of harmonics linearly but not their magnitude. However, related time-domain response may be greatly affected. These characteristics of the harmonics are observed using the dynamic harmonic domain analysis which calculates exact variations of harmonics. To such aim, a phase-shifting matrix is defined which provides exact phase-shift calculation considering each harmonic order. The introduced concept significantly reduces the required simulation time and represents the effects of the source phase angle on the harmonic content and time-domain response without performing extra simulations. Finally, the novel concept is successfully applied to two test cases, followed by analysis and discussion.