Browsing by Author "Ozer, Ishak"

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Comparison of Current Ratio Errors of Support and Toroidal Type CTs in Electric Power Systems: A Case Study
(IEEE-Inst Electrical Electronics Engineers Inc, 2025) Ozer, Ishak; Unluturk, Ali
A current transformer (CT) is a specialized device used to reduce high current values to safe and manageable levels in measurement and protection systems. Current ratio error (CRE) is an inevitable error in CTs due to factors such as magnetic saturation, magnetic core properties, primary and secondary winding errors, temperature effects and frequency changes, and manufacturing tolerances. Keeping this error close to zero is critical to the reliability of Electric Power System (EPS) because it directly affects the operation of protective relays and the accuracy of energy measurement systems. This study has performed a field-based quantitative comparison of absolute percentage current ratio error (AP-CRE) between S-CTs and T-CTs within ARAS's (Erzurum/Turkey) operational electric power system (EPS). The AP-CRE measurement has been obtained from S-CTs and T-CTs in EPS for protection with accuracy class 5P. Experimental measurement tests on a total of 34 CTs, including 17 S-CT and 17 T-CT, actively used in EPS. AP-CREs have been obtained by means of the TURA-01 device. In addition, during each AP-CRE measurement, absolute phase displacement (A-PD) and excitation current values have been also measured in real time. The performance of S-CT and T-CT have been evaluated based on three main metrics: mean absolute error (MAE), root mean square error (RMSE) and standard deviation (STD) values of the AP-CRE values obtained from CTs. According to AP-CRE; T-CT: MAE=0.44, RMSE=0.47 and STD=0.15, while S-CT: MAE=0.55, RMSE=0.58 and STD=0.21. The AP-CRE performance proves that T-CTs are better than S-CTs in EPS, which increases reliability.
Optimization Based Control of Overcurrent Relays in Distribution Network Considering Real-Time Measurements: A Case Study
(Elsevier Sci Ltd, 2025) Unluturk, Ali; Ozer, Ishak
The coordination time interval (CTI) is very important in the coordination of overcurrent relays (OCRs). Although the CTI constraint is usually taken as 0.2 in the literature, it is also stated that it can be taken at different values. In the relay coordination carried out on a real power system serving in Erzurum/Turkey, the triping delay times (TDT) of OCRs and the contact opening delay times (CODT) of circuit breakers (CB) were measured and the CTI constraints in the coordination were determined according to the obtained measurements. This coordination process was transformed into an objective function (OF). This OF was solved with metaheuristic optimization algorithms. The Dandelion Optimization (DO) solution is better than spider wasp, golden jackal, zebra and dingo based optimization. Then, time multiplier setting (TMS) values are obtained from OF according to the CTI value determined according to the proposed real-time measurement and the CTI = 0.2 value frequently preferred in the literature. The performance of the relay TMS values obtained according to the proposed and classical methods was compared. Considering the power model and solution, 18.67% improvement in the operation times of the relays was achieved in Relay 2, 11.67% in Relay 3, 19.94% in Relay 4, 28.6% in Relay 6 and 23.31 % in Relay 7. The TMS value of Relay 5 is the same for the proposed and the classical method. As a result, the fast operation, reliability and selectivity of the power system were improved by ensuring correct relay coordination with the proposed method.