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Development of a field data-based virtual test bed for microgrid integration of building automation technologies

Microgrid is one of the promising solutions to achieving sustainable and efficiently operating power systems. With increasing number of distributed generators, dispersed storage systems and advancing load control capabilities, microgrids are going to play an important role in the future smart grid structure. The recent focus in this area of study is on using the field data gathered from pilot applications to develop virtual test beds to be used during replication, testing of various cases and estimating long term outcomes of microgrids with different specifications. This paper describes development of a virtual test bed focused on analyzing microgrid and utility power flow relations using the field data and energy management logic of a microgrid laboratory. In addition to modeling a flexible structure that can be scaled and modified according to research interests, a KNX controlled dimmer is also simulated for analyzing the integration of an existing home automation technology into microgrid control actions.

Insulator contour optimization using intelligent systems & soft computational methods

The purpose of this study is to give basic concepts of insulator contour optimization by using intelligent systems and soft computational methods. In this sense, artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) are used as an optimization method. First training and validation data were collected from electric field distribution of an insulator by using finite element method analysis. Data contains coordinates and electrical field values of the middle point and the top point of the insulator. Then the data sets were used as inputs for ANN and ANFIS to train the algorithms. After the training process, any desired output that the top radius of the insulator was calculated for given input data using both methods. Finally results were compared from each other. The methods successfully are used for insulator contour optimization.

Mitigation of negative impacts of distributed generation on LV distribution networks through microgrid management systems

Renewable based distributed generation (DG) particularly in low voltage (LV) distribution networks may cause voltage limit violations, line overloads and increase in network losses. Siting and sizing of DG penetrations are generally done according to the worst case scenarios. However, since these cases occur rarely in long term operation, a realistic design enables more DG penetration. There are numerous conventional methods, each having several benefits and drawbacks. Local energy management systems can also be part of the solution. This study investigates the negative steady state operational impacts of DG on LV distribution networks and proposes a microgrid management approach to mitigate those impacts. A field data-based virtual test bed is used to simulate undervoltage and overvoltage issues and a microgrid energy management approach is developed and tested to minimize the negative impacts on the network. Moreover, Digital Audio Broadcasting (DAB) as data transmission means in microgrids, is discussed as an adaptable communication solution for its real-world implementation.

Numerical analysis of a metal-oxide surge arrester by using finite element method

This paper presents the numerical analysis of the voltage-current relationship of a metal-oxide surge arrester by using Finite Element Method. In the analysis as an application example, a surge arrester with 123 kV rated voltage was taken into account. The surge arrester was studied by using a 2D axi-symmetrical model. The nonlinear V-I characteristics of the metal-oxide resistors was approximated by a power curve, and non-linear volume conductivity which depends on either voltage or current was defined for the resistor elements. The simulations in both AC and impulse current conditions were performed for the surge arrester. In the AC simulations, electric field and electric potentials were obtained along the resistor blocks as well as along the creepage path of the surge arrester. In the transient simulations, an impulse current with 8/20 μs wave shape was applied to the surge arrester, and the residual voltage across the surge arrester were obtained by the proposed modeling method.

Line surge arrester application for a 380 kV power transmission line

In this study, an application of a line surge arrester was presented for a 380 kV Turkish Power Transmission Line by using PSCAD simulation software. Simulations were limited to the over-voltages caused by the lightning surges. Real system data was used for a representative transmission line, which was subjected to relatively higher number of outages in the past. The simulations were performed to determine the lightning impulse voltages across the insulator terminals. Effects of several parameters, such as configuration of the transmission tower, tower grounding resistances, surge impedances of the transmission and ground wires, front time and the magnitude of the lightning impulse currents to the overvoltage across the insulator terminals were considered in the simulations. Moreover, locational effects of the lightning strikes on the overvoltages across the insulators were investigated. After modeling the transmission lines and the lightning current, line surge arrester was modeled by its non-linear behavior in the simulations. Finally, optimal allocation of the line surge arrester was determined in the transmission lines, satisfying the desired insulation for the transmission system. All the scenarios were compared in terms of the magnitude of the lightning overvoltage across the insulator units.

Travelling wave fault location on hybrid power lines

Detection and location of faults on power systems have great importance in term of being able to clear faults in a short time and provide more available service to customers. Since sensitive determination of fault location is necessary, it is required to measure the arrival time of the travelling waves accurately and to use corresponding propagation velocity of the cable. However, when a fault location scheme is utilized for this purpose, which uses the velocity of the propagation as a parameter during analysis, changing parameters of the cable over its age, such as relative permittivity, introduce large errors in determination of the fault locations. On the other hand, hybrid systems including cable and overhead lines makes the detection of fault location more difficult. Therefore, in order to have precise fault localization, the successful analysis should not use the velocity of propagation especially for the aged cables. This paper describes the use of wavelet analysis for identifying fault location on power lines without using the velocity of propagation. Extensive simulation work has been done in order to check the effectiveness of the proposed scheme based on wavelet analysis. Different fault scenarios have been utilized on a given power system model. The obtained results indicate that the proposed scheme is effective and able to locate the points of faults with reasonable accuracy. This scheme can also be further used for the travelling wave protection on power systems to provide fast and accurate fault clearance.

Analysis of critical operating conditions for LV distribution networks with microgrids

Increase in the penetration of Distributed Generation (DG) in distribution networks, raises the risk of voltage limit violations while contributing to line losses. Especially in low voltage (LV) distribution networks (secondary distribution networks), impacts of active power flows on the bus voltages and on the network losses are more dominant. As network operators must meet regulatory limitations, they have to take into account the most critical operating conditions in their systems. In this study, it is aimed to present the impact of the worst operation cases of LV distribution networks comprising microgrids. Simulation studies are performed on a field data-based virtual test-bed. The simulations are repeated for several cases consisting different microgrid points of connection with different network loading and microgrid supply/demand conditions.

Design principles and performance analysis of a wimshurst generator

Wimshurst generator is an electrostatic machine that produces high DC voltages by induction. The class of electrostatic machine that Wimshurst belongs to is influence machines. Because the charges are distributed on the machine by influencing each other to have cumulative charge generation. Two opposite rotating insulator disks with metal sectors on it distribute the charges such a way that, negative charges are collected in one capacitor, positive charges in the other. In this study, a Wimshurst generator is designed and constructed using commonly available materials.

Analyzing and denoising of impulse voltage waveforms using multi-resolution wavelet analysis (MRA)

In this study, full impulse voltage data measured from an experimental setup were analysed and denoised using multi resolution wavelet analysis. Effect of decomposition level was investigated and optimum decomposition level was determined for each impulse voltage waveform. The wavelet function type is not changed in each analysis. It is traced that obtained noiseless signal was convenient with those calculated by empirical formulas.