Applied sciences

Archives of Electrical Engineering

Content

Archives of Electrical Engineering | 2018 | vol. 67 | No 2

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Abstract

Partial discharges (PD) are influencing electrical insulating systems of high voltage electrical devices. Typically, in laboratory and diagnostics AC tests focused on measuring and analysis of PD, a pure sinusoidal voltage waveform is assumed. However, in practice the spectral content of the working voltage is rarely so ideal and additional spectral components have a significant impact on the discharge behaviour in electrical insulation systems. In this paper the influence of voltage harmonics on PD behaviour and phase-resolved PD patterns evolution is analysed. The presented experiments were conducted on a specimen representing a gaseous inclusion embedded in electrical insulation. The experimental results showed that various harmonic compositions superimposed on the fundamental sinusoidal waveform have a significant impact on PD intensity and maximum charge. In consequence, the derived patterns of PD phase, and magnitude distributions are distorted, and statistical parameters calculated on their basis are changed. In certain en- vironments, neglecting harmonic content in the testing voltage may lead to a misleading interpretation and assessment of PD severity.
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Authors and Affiliations

Marek Florkowski
Barbara Florkowska
Paweł Zydroń
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Abstract

Finding the most critical contingencies in a power system is a difficult task as multiple evaluations of load and generation scenarios are needed. This paper presents a mathematical formulation for selecting, ranking, and grouping the most critical N-1 network contingencies, based on the calculation of a Power Constraint Index (PCI) obtained from the Outage Transfer Distribution Factors (OTDF). The results show that the PCI is only affected by the impedance parameter of the transmission network, the topology, and the location of all generators. Other methods, such as the Performance Index (PI) and the Overload Index (OL) are affected by the power generation and demand variations. The proposed mathematical formulation can be useful to accelerate the calculation of other methods that evaluate contingencies in power system planning and operation. Furthermore, the fast calculation of indices makes it suitable for online evaluation and classification of multiple events considering the current topology. The results showed that the proposed al- gorithm easily selected and ranked the expected contingencies, with the highest values of the index corresponding to the most critical events. In the filtering process, the computa- tional calculation time improved without losing the robustness of the results.
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Authors and Affiliations

Oswaldo Arenas-Crespo
John E. Candelo
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Abstract

This paper proposes a new dc-side active filter for wind generators that combines 12-pulse polygon auto-transformer rectifier with dc-side current injection method and dual-buck full-bridge inverter having not the “shoot-through” problem in conventional bridge-type inverters, and therefore this system with the character low harmonic distortion and high reliability. The proposed dc-side active filter is realized by using dual-buck full bridge converter, which directly injects compensation current at dc-side of two six-pulse diode bridges rectifiers. Compared with the conventional three-phase active power filter at ac-side, the system with the dc-side active filter draws nearly sinusoidal current by shaping the diode bridges output current to be triangular without using the instantaneous reactive power compensation technology, only using simple hysteretic current control, even though under load variation and unbalanced voltage disturbances, and while an acceptable linear approximation to the accurate waveform of injection current is recommended. The perfor- mance of the system was simulated using MATLAB/Simulink, and the possibility of the dc-side active filter eliminating current harmonics was confirmed in steady and transient states. The simulation results indicate, the system has a total harmonic distortion of current reduced closely to 1%, and a high power factor on the wind generator side.
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Authors and Affiliations

Xiao-Qiang Chen
Shou-Wang Zhao
Ying Wang
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Abstract

The paper presents an identification procedure of electromagnetic parameters for an induction motor equivalent circuit including rotor deep bar effect. The presented proce- dure employs information obtained from measurement realised under the load curve test, described in the standard PN-EN 60034-28: 2013. In the article, the selected impedance frequency characteristics of the tested induction machines derived from measurement have been compared with the corresponding characteristics calculated with the use of the adopted equivalent circuit with electromagnetic parameters determined according to the presented procedure. Furthermore, the characteristics computed on the basis of the classical machine T-type equivalent circuit, whose electromagnetic parameters had been identified in line with the chosen methodologies reported in the standards PN-EN 60034-28: 2013 and IEEE Std 112TM-2004, have been included in the comparative analysis as well. Additional verification of correctness of identified electromagnetic parameters has been realised through comparison of the steady-state power factor-slip and torque-slip characteristics determined experimentally and through the machine operation simulations carried out with the use of the considered equivalent circuits. The studies concerning induction motors with two types of rotor construction – a conventional single cage rotor and a solid rotor manufactured from magnetic material – have been presented in the paper.
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Authors and Affiliations

Jarosław Rolek
Grzegorz Utrata
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Abstract

This paper presents an enhanced internal model control (EIMC) scheme for a time-delayed second order unstable process, which is subjected to exogenous disturbance and model variations. Even though the conventional internal model control (IMC) can provide an asymptotic tracking response with desired stability margins, the major limitation of conventional IMC is that it cannot be applied for an unstable system because a small exogenous disturbance can trigger the control signal to grow unbounded. Hence, modify- ing the conventional IMC structure to guarantee the internal stability, we present an EIMC scheme which can offer better trade-off between setpoint tracking and disturbance rejec- tion characteristics. To improve the load disturbance rejection characteristics and attenuate the effect of sensor noise, we solve the selection of controller gains as an H¥ optimization problem. One of the key aspects of the EIMC scheme is that the robustness of the closed loop system can be tuned via a single tuning parameter. The performance of the EIMC scheme is experimentally assessed on a magnetic levitation plant for reference tracking application. Experimental results substantiate that the EIMC scheme can effectively coun- teract the inherent time delay in the model and offer precise tracking, even in the presence of exogenous disturbance. Moreover, by comparing the trajectory tracking performance of EIMC with that of the proportional integral velocity (PIV) controller through cumulative power spectral density (CPSD) of the tracking error, we show that the EIMC can offer better low frequency servo response with minimal vibrations.
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Authors and Affiliations

Vinodh Kumar Elumalai
Raaja Ganapathy Subramanian
Joshua Sunder David Reddipogu
Soundarya Srinivasan
Shantanu Agrawal
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Abstract

A solar photovoltaic (PV) system has been emerging out as one of the greatest potential renewable energy sources and is contributing significantly in the energy sector. The PV system depends upon the solar irradiation and any changes in the incoming solar irradiation will affect badly on the output of the PV system. The solar irradiation is location specific and also the atmospheric conditions in the surroundings of the PV system contribute significantly to its performance. This paper presents the cumulative assessment of the four MPPT techniques during the partial shading conditions (PSCs) for different configurations of the PV array. The partial shading configurations like series-parallel, bridge link, total cross tied and honeycomb structure for an 8×4 PV array has been simulated to compare the maximum power point tracking (MPPT) techniques. The MPPT techniques like perturb and observe, incremental conductance, extremum seeking control and a fuzzy logic controller were implemented for different shading patterns. The results related to the maximum power tracked, tracking efficiency of each of the MPPT techniques were presented in order to assess the best MPPT technique and the best configuration of the PV array for yielding the maximum power during the PSCs.
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Authors and Affiliations

B. Krishna Naick
K. Chatterjee
T.K. Chatterjee
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Abstract

Nowadays, the development of smart grids has been the focus of attention due to its advantages for power systems. One of the aspects of smart grids defined by using distributed generation (DG) in a low voltage network is a microgrid (MG). Based on its operational states, MG can operate in different configurations such as grid-connected mode or off-grid mode. The switching between these states is one of the challenging issues in this technical area. The fault currents in different buses have higher value compared to islanded mode of MG when the MG is connected to the main grid, which influences the protection equipment. In this situation, some electrical devices may be damaged due to the fault currents. Application of a fault current limiter (FCL) is considered as an effective way to overcome this challenge. The optimal size of these FCLs can optimize the performance of an MG. In this paper, an index for FCL size optimization has been used. In addition, two optimization algorithms (Bat Algorithm and Cuckoo Search Algorithm) have been applied to the problem. The application of an FCL has been studied in grid-connected and islanded-mode. In addition, the application of the capacitor bank in both modes has been investigated. The results of simulations carried out by MATLAB have been presented and compared.
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Authors and Affiliations

Ali Asghar Khodadoost Arani
N. Bayati
Reza Mohammadi
G.B. Gharehpetian
S.H. Sadeghi
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Abstract

This paper presents simulation and experimental results obtained with a Dead-Beat predictive current controller for a Permanent Magnet Synchronous Machine (PMSM) drive system. With means of combined field and circuit simulations, an efficiency map and required current in a direct- and quadrature-axis are defined. A control algorithm was implemented within an open-i