Faruk Aras

Lifetime estimation and monitoring of power transformer considering annual load factors

This paper focuses on the realistic remaining service life prediction and monitoring system of power transformers, using an algorithm developed by the authors. The power transformer is one of the vital components of power transmission and distribution substations. It is important to know the loading capacity and remaining service life of a power transformer to ensure its economical and secure operation. This information is directly related to the condition of cellulosic insulation. According to classical method of prediction, the power transformer is considered to be operated under constant load for the remainder of its lifespan. However, in reality the load factor varies continuously, and this is a key factor affecting the service life of power transformers. In this study, a realistic method for monitoring and predicting the service lifetime of power transformers is presented by considering annual load factors. The proposed method is applicable to any power transformer and can be updated by considering relevant standards for different liquid and solid insulation materials. As a case study, life-loss calculation and the remaining service life predictions are carried out using a thermal model that has been created considering a 250 MVA mineral oil-immersed power transformer.

An Assessment of the Methods for Calculating Ampacity of Underground Power Cables

Endurance of an insulation material to high temperatures determines the maximum current-carrying capacity (ampacity) of an underground power cable. Cable ampacity is calculated conventionally using the installation conditions and maximum steady-state operation temperature according to IEC-60287 standard. In this article, finite element method results are compared with IEC-60287. A further verification has also been made with experiments. In this work, ampacity analyzes of 154 kV high voltage XLPE underground power cable are made using ANSYS 5.61 finite element analysis software. An experimental set-up is developed to measure conductor and surface temperature of the cable in underground conditions. The results of experiments and numerical calculations are compared to the IEC-60287 standard. Additionally, the thermal regions of three cables in flat installation are investigated to show the versatility of the finite element method. The effects of insulation thickness and external thermal source on ampacity are also analyzed using the finite element method.

An assessment on aging model of IEEE/IEC standards for natural and mineral oil-immersed transformer

This paper presents an assessment on aging model of IEEE and IEC standards using thermal model of oil-immersed power transformer for natural ester and mineral oil. For this purpose, a model created for the analysis of behavior transient thermal performance with aging both of natural ester and mineral oils. Thermal model of the transformer is based on thermal-electrical analogy that is calculated separately for natural and mineral oils covering top-oil and hot-spot temperatures. The hot-spot temperature values of each ester/oil are used to calculate aging parameters which include the aging acceleration factor, time dependent relative aging rate and insulation life loss variations.

3D Virtual Classroom Environment for Teaching Renewable Energy Production and Substation Equipment

In this investigation, a virtual classroom for Uşak Universitys Electricity Program is designed, implemented and then tested by using the 3D virtual environment Second Life. When online, learners and instructors are able to correspond with each other by using their own avatars, chat vocally, make presentations and watch videos, as well as utilise all opportunities of a 3D virtual environment. Furthermore, learners can access the educational materials of the Electricity Program and interact with each other even when the educator is not available, giving opportunities for both synchronous and asynchronous distance education. The 3D virtual environment is analysed and evaluated here in terms of education costs, and advantages or disadvantages for both learner and educator.

An assessment on distance education in a 3D virtual environment: How to produce electricity in a hydroelectric power plant

In this study, a web-based 3D virtual environment well known the Second Life (SL) that people can be connected from all over the world, has been introduced and investigated the benefits on the distance education (DE). In the SL 3D virtual environment, a hydroelectric power plant has been built to understand how to produce electricity, and also students can observe the details of the plants structure and parts which cannot be shown even in a technical trip due to the plant is in-service. A few students interested in this topic have been taught and trained at distance access. At the end of this study, the SL 3D virtual environment has been evaluated the contributions on the DE and e-learning systems.

Investigation of Harmonic Effects on Underground Power Cables

In this study, the effects of harmonics on underground power cable are investigated considering a real system. For this purpose, firstly, harmonic measurements were carried out under middle voltage in underground distribution cable system and then a Matlab/Simulink model has been constituted under the light of the measured data. The results indicate that the harmonics cause the excessive temperature rise due to the power losses in the cable conductor and the cable life is affected by the temperature rise. Therefore a derating factor is purposed to reduce the cable ampacity in this study as well.

Thermal modelling and analysis of high-voltage insulated power cables under transient loads

This article presents a simple thermal model for transient analysis of high‐voltage underground power cables based on proper ladder diagram at MATLAB–Simulink software under various operating conditions for engineering students. Available commercial programs created with commercial worries are not suitable for students during the learning process, which involve different applications on power cable analysis. The model gives an opportunity for students to solve the often‐faced transient problems in utilities. The transient model of the underground power cable system using the analytic procedures based on IEC60853 standards is presented with an example solution of the 154 kV power cable in service in Turkish transmission system in this article.

Laboratory Experiments for Electrical Insulation Courses Using a New High-Voltage Cell

The objective of the study is to introduce the use of a computer-aided designed high-voltage cell for teaching electrical insulation. The cell allows students to make real applications in high voltage (HV) topics taught in a single-semester course for senior undergraduate students. The system is constituted of two main parts. The first part is a metal cell which consists of a 220 V/0-100 kV HV transformer, a variable transformer driven by an a.c. motor and a motor driver. The second part is a hand-made electrode system made of tempered glass. The system was controlled manually or automatically using a Programmable Logic Controller (PLC), an operation panel and a computer. In experiments, polyester films are used at various thicknesses as a solid insulation, and transformer oil is also used as a liquid insulation. Each student measures the breakdown voltages under various conditions for solid and liquid insulation using this system. Dielectric strength and ageing of the insulation were determined by computing the mean of the data obtained by each group of students from the experiments. The results and educational benefits are also presented in this paper.

A Novel Gui Simulation Program Designed for Teaching of Underground Power Cables

This paper presents a novel computer simulation program designed to aid teaching process in course of underground power cables for engineering students. The calculation of power cable ratings uses several different formulas and long analytical processes based on IEC 60287 and IEC 60853 standards. Therefore it is difficult to examine different variations such as power cable properties, installations and operation conditions, during the restrictive lesson time. For these reasons, a program has been developed to use for teaching process of the power cable course. The program allows the users to effectively learn the rating of underground power cables under different operation conditions with illustrative figures. The program details are presented and explained in this paper.

Investigation on aging mechanism of polyester under combined stresses

The physical properties of polyester film, such as thermal stability, combined with its mechanical properties, such as tensile break strength, and its electrical strength make it the preferred material for a wide variety of electrical insulation applications. Therefore, polyesters are widely used as insulating material for electric power system equipment such as cables, motors, transformers, and capacitors, since its high dielectric constant and resistance to degradation in high voltage and thermal stresses makes it ideal for mechanical barriers in wire and cable applications. For instance, in transformers and other high-voltage distribution equipment, polyester film is used to wrap the conductors [1]-[3].