Aydogan Ozdemir

Branch outage simulation for MVAr flows: bounded network solution

Almost all of the methods developed thus far to calculate the post outage quantities in an electric power system use linear models for the sake of computational efficiency. Linear models, however, may cause relatively large computational errors especially for reactive power flows. This paper presents a new line outage simulation method for reactive power flows that minimizes the errors resulting from the use of linear system models. The proposed method formulates a line outage as a local nonlinear constrained optimization problem. Optimization is used as a feedback to correct the errors resulting from linearized equations. The method provides more accurate calculation of post-outage load bus voltage magnitudes with less computational effort. The method is applied to IEEE test systems and the results are compared with those obtained using the full power flow.

380 kV corona ring optimization for AC voltages

This paper presents corona ring optimization for 380 kV V-insulator string composed of glass insulator units. The influence of the corona ring design parameters are examined not only with regard to 3D simulations but also laboratory tests. The purpose of the simulations is to find reasonable corona ring design parameters such as corona ring diameter, corona tube diameter and installation height on the point of effective field regulation around the critical region of the string. Indoor laboratory tests including radio interference voltage levels, corona inception voltages and ac flashover voltages are conducted on the centre phase of a full scaled tower both for experimental based corona ring design as well as verifications of the simulations. After both simulations and experimental based investigations, appropriate corona ring design parameters for the string are determined for effective field regulation, minimum interference level, ac flashover performance and economic point of view.

Comparison of Post Outage Bus Voltage Magnitudes Estimated by Harmony Search and Differential Evolution Methods

Contingency studies are indispensable tools of both the power system planning and operational studies. Real time implementation of operational problems makes necessary the use of high speed computational methods while requiring reasonable accuracies. On the other hand, accuracy of the results and the speed of calculation depend on branch outage modeling as well as solution algorithm used. This paper presents a comparison of post outage bus voltage magnitudes calculated by two meta-heuristic approaches; namely differential evolution (DE) and harmony search (HS) methods. The methods are tested on IEEE 14, IEEE 30, IEEE 57, and IEEE 118 bus test systems and the results are compared both in terms of accuracy and calculation speed.

Contingency selection based on real power transmission losses

This paper presents two new performance indices for contingency analysis in a composite electric power system. The proposed indices are derived from active power transmission losses that do not require additional parameters. They can be used effectively for line overloading and bus voltage limit violation performance indices. Their effects are tested on an IEEE RTS and the results have shown that they can be used effectively instead of the conventional ones.

Effects of corona ring design upon impulse voltage withstand level of 380 kV V-strings

This study presents the influence of corona rings on impulse withstand performance of 380 kV V-insulator strings. Those strings comprising cap-and-pin type glass insulator units are one of the most common configurations in Turkish National Power Transmission System. Laboratory test setup was constructed for the centre phase of a full scaled tower. Laboratory tests are performed to investigate the lightning and switching impulse performance of the strings equipped with the existing racket type corona rings and the circular type corona rings. Withstand voltages, lower flashover probability levels, flashover routes and times to flashovers are determined under dry and wet test conditions. In addition, some 3D field simulations regarding potential and electric field distributions are also performed for the interpretation of insulator surface flashovers.

Component-based load modeling including capacitor banks

A well-known practical approach to load modeling is the component-based method via several processes; component load modeling, composition rate estimation and aggregation of component loads, aggregation of distribution system and so on. There is often an error between the model output and the measured value in reactive load because of the core losses of transformers, the line losses and the capacitor banks. This paper presents an improved component-based load model which minimize an error for reactive load model considering the actual configuration of the substation and the classification method of component load characteristics by quantitative analysis for component loads to group. In addition, load characteristic tests are per-formed to obtain reliable data based on the statistical theory for the component load modeling.

Ac and transient electric field distributions along a 380 kV V-string insulator

This paper presents the results of a study of the ac and the transient electric field distributions along a 380 kV V-string of glass cap-and-pin suspension insulators. The transmission tower, conductors and insulators are modeled in 3D, and COMSOL 4.2 is used for the finite element simulations. The insulators are modeled both for clean and for the polluted cases. The pollution layer is modeled by a wet conductive layer of 2 mm thickness on the insulator surface and the conductivity of the layer is varied between 10-8 to 1.0 S/m. The permittivity of the pollution layer is assumed to be 81. Clean, full pollution and partial pollution cases are taken into consideration. The effects of corona rings on the field distributions are also investigated by 3D simulations.

Fuzzy logic based MW contingency ranking against masking problem

The main objective of an electric power system planning and operation is to maintain the system security while respecting certain constraints imposed on the system. As a framework of security, it is important to investigate the influence of potential failure states on the system performance in advance. Contingency ranking quantifies the severity of each outage with a scalar performance index, by which all possible contingencies can be ranked. Low order performance indices are preferred for the sake of computational efficiency. However, they cannot succeed in accurate ordering because of masking effect. This paper presents a fuzzy logic based MW contingency ranking algorithm for line outage contingency analysis, which minimizes the masking effect. Following the presentation of theoretical basis, the proposed algorithm is applied to several test systems. The concordance of the resulting rankings and the actual rankings are tested with several statistical quantities.

RCM application for Turkish National Power Transmission System

This study presents a RCM program for Turkish National Power Transmission System. Depending upon the information from transmission utility staff, the system is decomposed into functional blocks and failures for each functional block is held individually to attain a reasonable maintenance program for the transmission system.

Simulations of pollution and their effects on the electrical performance of glass suspension insulators

This paper presents simulations of pollution and their effects on the electrical performance of cap-and-pin glass suspension insulators. The pollution is modeled by using a partially conductive epoxy resin with graphite powder. The effects of the pollution levels as well as their locations on the insulator surfaces are investigated for both simulation and experimental studies. The studies are conducted both for one suspension unit and a string of five insulators. The results show that at power frequency voltage, the reduction in the flashover voltage is about the same whether the upper surface or the bottom surface of the insulator is polluted. Moreover, the percentage reduction of a single unit is about the same as for a five unit string. At lightning impulse voltage, the insulator performance depends on the location of the pollution. Positive polarity impulse voltage is more critical than the negative polarity for the upper surface polluted case for one and the five unit string. For the bottom polluted case, negative polarity impulse voltage is more critical.