Canbolat Uçak

An analytical approach for step-by-step restoration of distribution systems following extended outages

Loss of diversity among loads may cause cold load pickup problems after an extended outage in distribution systems. Thermostatically-controlled devices such as air-conditioners, heaters, heat pumps, water heaters etc. become the largest portion of load during restoration. In this paper, an analytical approach for restoration of distribution systems during cold load pickup is presented. A delayed exponential model is used to represent the load during cold load pickup. A thermodynamic model of a transformer is used to determine the loading limits for this type of load. Whenever loading limits are reached, sections are restored step-by-step. In step-by-step restoration, the sequence of sections restored plays an important role in total restoration time. An optimal restoration sequence of different sections of the distribution system is determined for minimum total restoration time as well as minimum customer interruption duration. >

The effects of load parameter dispersion and direct load control actions on aggregated load

Determining and forecasting the load behavior in distribution systems are very important in both operational and planning stages. Increased penetration of thermostatically-controlled loads such as air-conditioners, water heaters, heat pumps, etc. has resulted in many investigations on how to determine an accurate dynamic of these loads. Thermostatically-controlled loads are also a candidate for the direct load control because of their thermal storage capabilities. In this paper, a load model based on stochastic difference equation is used to study the effects of the load parameters and the direct load control actions. Stochastic difference suitable for the computer analysis and is very simple to implement. By using this model, a Monte Carlo simulation is run for an example system. The effects of load parameter dispersion and different load actions are analyzed. The distribution of house temperatures is studied for control actions. The results for the load parameter dispersion and the direct load control actions on aggregated load for the example system are given and a discussion based on the results is provided in the paper.

Fault classification for power distribution systems via a combined wavelet-neural approach

This paper presents an integrated design of a fault classifier which uses a hybrid wavelet-artificial neural network (ANN) based approach. The data for the fault classifier is produced by PSCAD/EMTDC simulation program for 34.5 kV Sagmalcilar-Maltepe distribution system in Istanbul, Turkey. It is aimed to design a classifier capable of recognizing ten classes of three-phase distribution system faults. A database of line currents and line-to-ground voltages is built up including system faults at different fault inception angles and fault locations. The characteristic information over six-channel of current and voltage samples is extracted by the wavelet multiresolution analysis technique. Then, an ANN-based tool was employed for classification task. The main idea of this approach is to solve the complex fault (three-phase short-circuit) classification problem under various system and fault conditions. A self-organizing map, with Kohonens learning algorithm and type-one learning vector quantization technique is implemented into this study. The performance of the wavelet-neural fault classifier is presented and the results are analyzed in the paper. It is shown that the technique correctly recognizes and discriminates the fault types and faulted phases with a high degree of accuracy in the simulated model distribution system.

Optimal step-by-step restoration of distribution systems during excessive loads due to cold load pickup

Abstract Restoration of a distribution system following extended outages may cause problems if the substation transformer capacity cannot supply the initial load. Excessive initial load is a result of loss of diversity in the distribution system. Dividing the system into sections and restoring these sections step by step is one of the solutions to overcome excessive load due to cold load pickup. In step-by-step restoration, the order of restoration of sections becomes an important factor in increasing the reliability and decreasing the average customer interruption duration. In this paper, step-by-step restoration of a distribution system to utilize transformer capacity to the maximum extent and to minimize the customer interruption duration is studied.

Convergence and periodic solutions for the input impedance of a standard ladder network

The input impedance of an infinite ladder network is computed by using the recursive relation and by assuming that the input impedance does not change when a new block is added to the network. However, this assumption is not true in general and standard textbooks do not always treat these networks correctly. This paper develops a general solution to obtain the input impedance of a standard ladder network of impedances and admittances for any number of blocks. Then, this result is used to provide the convergence condition for the infinite ladder network. The conditions which lead to periodic input impedance are exploited. It is shown that there are infinite numbers of periodic points and no paradoxical behaviour exists in the standard ladder network.

Understanding the behaviour of infinite ladder circuits

Infinite ladder circuits are often encountered in undergraduate electrical engineering and physics curricula when dealing with series and parallel combination of impedances, as a part of filter design or wave propagation on transmission lines. The input impedance of such infinite ladder circuits is derived by assuming that the input impedance does not change when a new block of impedance is added. However, the impedance derived from this assumption may lead to incorrect conclusions if it is not treated carefully. Sometimes, in the literature, the input impedance behaviour of infinite ladder circuits is referred to as a paradox, leaving students and educators in doubt. This study intends to clarify this confusion and help to better comprehend the behaviour of the input impedance of infinite ladder circuits.

Dissipation, voltage profile and Lévy dragon in a special ladder network

A ladder network constructed by an elementary two-terminal network consisting of a parallel resistor–inductor block in series with a parallel resistor–capacitor block sometimes is said to have a non-dispersive dissipative response. This special ladder network is created iteratively by replacing the elementary two-terminal network in place of the resistors. In this paper, it will be demonstrated that, in fact, non-dispersive dissipative response conclusion of this special ladder network is not accurate for steady-state condition. Furthermore, the voltage profile of this special ladder network exhibits a fractal form called the Levy C curve or Levy dragon in a certain condition. Therefore, this special ladder network may be called the Levy ladder network. This ladder network might be interesting for physics and electrical engineering students and they may encounter when dealing with this network series and parallel combinations of impedances.

A dimmer circuit for various lighting devices

Incompatibility of compact fluorescent lamps (CFLs) and light-emitting-diodes (LEDs) with conventional light dimmers is a problem for consumers today. This paper proposes a dimmer circuit that is suitable for incandescent bulbs, CFLs and LEDs. Different kinds of lighting devices are studied and tested with AC and DC sources. The proposed dimmer circuit is designed, built and tested with various lighting devices. Experiments are performed in order to observe the electrical characteristic of the dimmer and optical characteristic of the lighting devices when they are used with the dimmer circuit. The experimental results show that the proposed dimmer can be used with these kinds of lighting devices within specific output voltage ranges.

INFRASTRUCTURE ENHANCEMENT FOR RESTORATION OF DISTRIBUTION SYSTEMS FOLLOWING EXTENDED OUTAGES

ABSTRACT Advances in micro-electronics, computers, and communications technology has made it possible to automate several functions in distribution systems. Such automation will make delivery of electricity more efficient, enhance reliability, and lead to more effective utilization and life-extension of existing electricity distribution infrastructure. Moreover, distribution automation offers opportunities for implementation of new functions. With certain enhancements in the distribution system infrastructure maximum benefits of distribution automation can be accrued. In this paper, an example of such infrastructure enhancement is presented. Specifically, application of remotely controlled three-phase and single-phase sectionalizers in restoration of power in distribution systems following an extended outage is presented. The remotely controlled sectionalizers can be opened and closed to supply power to specific parts of the system. Thus, restoration can be done in steps using these sectionalizers. Theref...