Volume 19, Issue 6 -

This article presents a model of Sparking Gap to be used in the Alternative Transients Program (ATP). The model includes the simulation of breakdown and a representation of the electric arc. The arc will be non-constrained and burn in air at atmospheric pressure, thus a discussion of the model and parameters to be used is presented. The effect of the arc on the interruption of current will be studied. Examples of power arc interruption following an impulse impact on a 230 kV transmission line are presented. The effects of interphase capacitive coupling and line length are discussed, in order to establish guidelines to allow successful reclosing operations.

Gas insulated metal-enclosed transmission line (GIL) is a substitute for overhead line, which is used for power transmitting in complicated geographical or geological environment In order to satisfying the requirements of operation in maintained state, each side of GIL needs to be installed a grounding switch. For the hybrid transmission system composed of GIL and double-circuit overhead line, the whole overhead line will be divided into incomplete transposed/non-transposed parts due to connection of GIL. When one of the grounding switches of GIL closes, it can lead to much greater induced current in each grounding switch. The induced voltage and current for hybrid transmission system will also change because of different parameters between GIL and overhead line. Calculation methods of induced voltage and current for hybrid transmission system with GIL are presented in this paper. Then, calculation conditions for hybrid transmission system are analyzed based on these evidences. Su-Tong GIL pipe gallery project is taken as an example for simulation in ATP/EMTP. Compared with traditional transmission system with overhead line, much higher performance requirements for grounding switches of Su-Tong GIL pipe gallery project are necessary, especially for induced current.

Leakage current measurement plays an important role in determining the healthiness of high voltage insulation of a power apparatus. High voltage (HV) insulation degrades due to electrical, thermal and mechanical ageing and their cumulative effects, and thus the leakage current of the insulation increase over a period of time. The accurate and real time measurement of leakage current enables the utilities to on-line access the healthiness of the insulation. This paper describes about the design, development, calibration and testing of a novel non-contact type passive leakage current sensor which can be used for monitoring of various electrical devices based on the analysis of the leakage current captured by the sensor. The developed sensor has been successfully used for measurement of leakage current in oil-filled HV bushings as well as in gas insulated surge arresters. The sensitivity of the developed sensor as per its design can be in the order of few milli amperes in case of bushing and in the order few micro amperes for surge arrester monitoring. The paper also reported a novel design of bushing adapter-sensor assembly for on-line measuring the leakage current in HV bushings without using the conventional capacitive or resistive tapping based measurements. Further, results covering experimental leakage current measurement on a 420 kV bushing using the developed adapter sensor assembly have also been presented. To establish capabilities of the developed sensor with optimized design parameters, laboratory measurements of leakage current on 420 kV and 145 kV GIS surge arresters have also been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has also been estimated in-line with IEC requirement to assess the healthiness of the surge arrester. Finally, suitability of the developed sensor for leakage current measurement of above power apparatus equipment has also been analyzed and discussed.

In this paper, a simple and fast approach is suggested for fault detection in transmission lines. The proposed technique utilizes a modified cumulative sum approach for a modal current to identify faults. The modal current is derived by proper linear mixing of three-phase currents. Since different types of faults may occur in transmission lines, all three-phase currents should be considered during fault analysis. By converting three-phase currents to a modal current, the processing time is reduced and less memory is needed. In this paper, a modal current is processed instead of three-phase currents. The modified cumulative sum approach presented in this paper is capable of decreasing computational burdens on the digital relay and accelerating the fault detection procedure. The proposed fault detection technique is evaluated in four different systems. Moreover, some real recorded field data were deliberated in the efficiency assessment of the proposed method. The results denote high accuracy and quickness of the proposed approach. Furthermore, the performance of the proposed methodology is compared with some other similar methods from different aspects.

Phasor Measurement Units have facilitated tracking of oscillations in power system response signals. This has provided an impetus for identifying unstable component modes directly from oscillatory signals. Prony analysis, the earliest method proposed for this purpose, throws up some trivial modes. These not only distract the analyzer but also prolong processing time thereby delaying corrective action. Hence the fitness metric chosen should serve to minimize the number of trivial modes. The conventional fitness metric is Signal-to-Noise Ratio (SNR), which is actually Signal-to- Estimation error Ratio (SER). This paper proposes that Mean Absolute Percentage Error (MAPE) can also serve well as a fitness metric. It is shown through case studies carried out on well-known four-machine power system that there are a few cases where MAPE performs better than SER while in some instances SER works better. This inference is verified even in the presence of measurement noise. Hence a novel fitness metric is proposed combining MAPE with SER. Case studies on simulated signals obtained from New England-power system prove that this novel metric can achieve considerable reduction in processing time. Besides, an exponential binary search has been suggested for determining the optimal model order in minimum number of iterations.

The relevance of the study is conditioned by the need to determine the state and residual life duration of high-voltage cable lines to identify faulty and maintainable cables. The aim of the article is to determine a reliable scientifically grounded criterion for assessment of insulation characteristics of the cables in use and to perform a comparative analysis of the results obtained by the traditional method of diagnosing insulation with the results of a new method of assessment by the return voltage. In this regard, the article deals with the issues related to the testing of cables having oil-impregnated paper insulation, as well as with the issue of switching from planned replacement of cables to assessment of their actual state and period of residual life. The authors propose to use the method of examining the cables by the return voltage using the device for testing electrical insulation “UDEI-1” developed at the department of Electrification and Automation of the Nizhny Novgorod State University of Engineering and Economics. The article presents the results of measuring the return voltage of three cables that operated under different conditions. The cables had different technical state. The analysis of the estimation of the residual life of cables by the return voltage was carried out using such criteria as the PIRV polarization index, the LIRV electrical conductivity index, and the P-factor. The P-factor is the physical criterion demonstrating the aging of paper-oil insulation by the shape of the return voltage curve. It represents such characteristics of insulation aging as moistening. To compare the results of testing the cables by the return voltage with the conventional methods of diagnostics and to determine the actual technical condition of power cables, the authors applied the method of spatiotemporal reflectometry and the method of measuring insulation resistance with the determination of such indicators of state as insulation resistance normalized per one kilometer, absorption coefficient, and polarization index. The results of this article confirm that the return voltage gives a qualitative assessment of the state and degree of aging of cables with impregnated paper insulation. The authors proposed a new system for evaluation of cable condition by weighting coefficients. In this approach, the determination of residual life of cables with impregnated paper insulation is based on the values of the return voltage. Application of the new system gives opportunity to improve reliability of the power lines. Recommendations for the further operation of the studied cables are given. The materials of the article are of practical value for carrying out complex assessment of the technical condition of power cables by the return voltage and can be useful for drawing up a schedule for replacement or repair of cable lines depending on their actual state.

Stator Flux Orientation Control Scheme (SFOCS) has limitations that its performance is mainly influenced by the tuning of parameters, the Proportional-Integral (PI) controller could not compensate system variations very efficiently. To overcome the drawbacks of PI controller the Fuzzy Logic Controllers (FLCs) are modelled. This paper presents the fuzzy logic based control strategy for the variable speed wind turbine generator by using Doubly Fed Induction Generator (DFIG). The mathematical model for DFIG is developed in synchronous reference frame by using SFOCS for current and voltage control and is discretized in time domain. Based on this model the artificial intelligence based FLCs are designed and implemented so as to improve the performance and efficiency of the system. This control scheme not only enhances the dynamic performance but also maintains almost unity power factor to the grid. In order to explore the robustness of the FLC and conventional PI controller, simulations are carried out for rapid variation of wind speed, and different disturbances generated in the system. The simulation results show that the proposed fuzzy logic based control strategies have better power control, faster oscillation damping, more accurate regulation, considerably reduced settling time and has fewer ripples in comparison with conventional PI controller. In the proposed SFOCS, the PI controllers are replaced with FLCs, to improve the performance and efficiency of the system. The system performance is analyzed for real and reactive power control in SFOCS for the effectiveness of synchronization with the grid.

With the trend of high proportion of renewable energy connecting with grid, peaking services has played a crucial role in the integration of wind power and other renewable energy sources. The current peaking service takes into account only the cost of thermal power units that providing peaking service without considering the impact of its own reliability on the peaking service and the safe operation of the power system. In this paper, the traditional uniform clearing mechanism has been improved, and the reliability factor of ancillary service provided by thermal power units has been included in the previous quotation-based sorting rule, and a multi-objective programming optimal purchasing model considering synergistic capacity cost and power system stability is established. According to the optimal solution of each objective, Pareto optimal solution of multi-objective programming problem is obtained by the ideal point method. Then the ancillary service price and purchase cost are obtained based on the solution.

In order to obtain the influence of wye (Y)-and delta (Δ\Delta)-connected winding on line start permanent magnet synchronous motor (LSPMSM), taking a 15 kW LSPMSM as an example, the two dimensional (2-D) finite element method (FEM) and analytical method are used to calculate the motor performance. The influence of 3rd harmonic current in Δ\Delta-connected winding on the motor electromagnetic field is analyzed. The difference of the losses and capacity of starting and overload between the Y- and Δ\Delta-connected winding are studied. Finally, combined with the related experiments, the correctness of the calculation model is verified and the reliability of the research results are proved.

The torque ripple, current fluctuation and variable switching frequency of conventional hysteresis current controller (CHCC) under different loading condition and motion variation is inevitable, which demands effective implementation of the existing current controller by which it will be possible to get rid of these limitations. This paper presents enhancement in performance of a vector controlled based Interior Permanent Magnet Synchronous Motor (IPMSM) drive system by using an adaptive hysteresis current controller (AHCC). This controller minimizes torque ripple, current error and is capable of providing nearly constant switching frequency by modifying its bandwidth according to the changes in the system parameter or when the system is subjected to any kind of disturbances and load variation. Initially the study is carried out in MATLAB-Simulink environment and then the test result is experimentally validated through hardware implementation with the help of DSP TMS320F2812 which provides a complete digital control system with high effectiveness and fast computational skill.

A projected high penetration of electric vehicles (EVs) in the electricity market will introduce an additional load in the grid. The foremost concern of EV owners is to reduce charging expenditure during real-time pricing. This paper presents an optimal charging schedule of the electric vehicle with the objective to minimize the charging cost and charging time. The allocation of EVs should satisfy constraints related to charging stations (CSs) status. The results obtained are compared with the two conventional algorithms and other charging algorithms: Arrival time-based priority algorithm (ATP) and SOC based priority algorithm (SPB), Particle Swarm Optimization (PSO) and Shuffled Frog Leaping Algorithm (SFLA). Also, the CS is powered by the main grid and the microgrid available in the CSs. The EVs charging schedule and the economic analysis is done for two cases: (i) With Grid only (ii) With Combined Grid & microgrid. The load shifting of EVs is done based on the grid pricing and the results obtained are compared with the other cases mentioned.

This paper proposes a comparative assessment of NN based current controllers followed by hardware validation towards power quality improvement in grid-interactive VSI controlled solar system. The steady state errors, transient disturbances and high current harmonic effects encountered in conventional linear PI and PR controllers are nullified by employing intelligent adaptive current controller. Three adaptive current control strategies viz. ADALINE-LMS, ALLMS, and VLAS-LMS are identified by using artificial neural network topology having been controlled by different weight-regulating algorithms which helps in minimizing current harmonics generated by the widespread use of VSI, non-linear loads, faults and uncertain polluted grid. A comprehensive comparative study is driven from the proposed adaptive controller's stability and convergence criterion, current magnitudes calculated at different power zones, % overshoot, settling time and power quality and analyzed under numerous operating conditions. From the comparative assessment performed in between conventional and intelligent current controllers, it is confirmed that the intelligent control technique performs best under the non-linear loads and transient conditions whereas all the controllers perform equally good under the linear loads. Proposed methods are simulated in MATLAB/Simulink and their effectiveness is compared in terms of time responses, stability and low-order current harmonics compensation capability. The robustness of the intelligent current controller is established through the experimental performances using dSPACE RTI 1202.

The variable-speed Permanent Magnet Synchronous Generator (PMSG) based Wind Energy Conversion System (WECS) attracts the maximum power from wind, but voltage-regulation and frequency-control of the system in standalone operation is a challenging task A modern-control-based-tracking of power from wind for its best utilization is proposed in this paper for standalone PMSG based hybrid-WECS comprising Battery Energy Storage System (BESS). An Adaptive Synchronous Reference Frame Phase-Locked-Loop (SRF-PLL) based control scheme for load side bi-directional voltage source converter (VSC) is presented for the system. MATLAB/Simulink model is developed for simulation study for the proposed system and the effectiveness of the controller for bi-directional-converter is discussed under different operating conditions: like variable wind-velocity, sudden load variation, and load unbalancing. Converter control scheme enhances the power smoothening, supply-load power-matching. Also it is able to regulate the active & reactive power from PMSG-BESS hybrid system with control of fluctuations in voltage & frequency with respect to varying operating conditions. Proposed controller successfully offers reactive-power-compensation, harmonics-reduction, and power-balancing. The proposed scheme is based on proportional & integral (PI) controller. Also system is experimentally validated in the laboratory-environment and results are presented here.