L. Kojovic

Bio: L. Kojovic is an academic researcher. The author has contributed to research in topics: Current transformer & Protective relay. The author has an hindex of 1, co-authored 1 publications receiving 72 citations.

Rogowski coils suit relay protection and measurement ~of power systems\

Abstract: Microprocessor-based technology has been accepted today in virtually all areas of electrical engineering, including power. Input signals that accurately replicate events are critical for the proper operation of microprocessor-based equipment. Therefore, current sensors are an integral element of relay protection and current measuring systems. Current transformers (CTs) have been used exclusively for protection and measurement applications in part because of their ability to produce the high power output needed by electromechanical equipment. The introduction of microprocessor-based equipment has made the high-power output of CTs unnecessary and made the use of other measurement techniques possible. One such measuring device that does not produce high-power output but offers many advantages over CTs is the Rogowski coil. This article describes Rogowski coil operational characteristics and it applications for current measurements.

PCB Rogowski coils benefit relay protection

Abstract: Innovative Rogowski coils enable the design of advanced protection systems when used with new multifunction relays and fiberoptic communication. The protection systems have faster response times to faults and can easily adjust to load and/or power system configuration changes. Since the new Rogowski coils are very accurate and do not saturate, protection levels can be set to lower fault current thresholds, reducing the stress on the protected equipment. The whole system is immune to external magnetic fields and has self-testing logic. No wiring is necessary.

Evaluation of Flexible Rogowski Coil Performances in Power Frequency Applications

Abstract: This paper investigates the effects of some influence quantities on the measurement of power frequency sinusoidal currents by means of flexible Rogowski coil sensors. The analysis is carried out through a numerical model, which is specifically developed and allows both the prediction of the circuital and coil parameter effects and the improvement of the coil design. The estimate of the measurement uncertainty associated with the on-site use of a flexible and openable Rogowski coil is finally given by assuming relatively controlled operating conditions.

Modeling and experimental verification of on-line PD detection in MV covered-conductor overhead networks

Abstract: The falling trees on covered-conductor (CC) overhead distribution lines produce partial discharges (PDs). The measurements have been taken in the laboratory and PD signal characteristics under various circumstances have been described. In this paper, an on-line single-phase PD monitoring system using Rogowski coil is simulated in EMTP-ATP. The simulation results are compared with those obtained from the laboratory measurements. The proposed model can be used to estimate the length of the practical CC lines at which PDs due to falling trees can be detected and localized; thus, deciding the number and positioning of the sensors over a particular length of the CC lines. The different noise sources have been described that cause interference with low level PD signals, which is a major challenge for on-line/on-site condition monitoring. The design aspects of the wireless sensor for this specific application are also discussed. Automatic detection of falling trees will reduce visual inspection work after storms and it will improve reliability and safety of the CC distribution system.

Calibration of on-line partial discharge measuring system using Rogowski coil in covered-conductor overhead distribution networks

Abstract: Partial discharge (PD) detection has been regarded as one of the most effective on-line predictive maintenance test and diagnostic tool for the condition monitoring of high voltage (HV) equipment. In this study, a methodology for detecting on-line PDs produced because of falling trees on the covered-conductor (CC) overhead distribution lines is introduced and calibration of PD measuring system is carried-out. The Rogowski coil is used as a PD sensor which is non-intrusive and superior to the conventional PD detectors. The experimental set-up was arranged in the HV laboratory for real-time analysis and a pulse calibrator was used to calibrate the PD measuring system. Few real-life PD measurements have been taken and it is revealed that PD magnitudes and signals bandwidth may vary under various circumstances. The calibrated on-line PD measuring system can be used to detect and measure the amount of PDs produced because of falling trees on CC lines, thus improving the reliability and safety of the distribution networks as well as reducing visual inspection work after storms.

Application of Rogowski Coils used for Protective Relaying Purposes

Abstract: This paper describes current technology and application for Rogowski coils, which serve in the role of current transformers for measuring power system currents for protective relaying or other measurement purposes. Rogowski coils have low-energy outputs. They offer a number of application advantages including compact size, light weight, and linearity (do not saturate like conventional iron-core current transformers). A forthcoming Guide PC37.235 from the IEEE PSRC will give detailed information and help for users