 |
 |
 |
|
Abstract and Manuscript Management System - Abstract Detail |
|
| Main Menu | Abstracts | |
| Speaker: | |
| Title: | |
| Topic Group: | |
| E-mail: | |
| Co-Authors: | |
| Abstract: |
It has been almost a century since coils uniformly wound on air-cores - Rogowski coils - have been described [1]. During that period they found a number of applications in power systems for current sensing, such as protective relaying, measurements of high currents, impulse currents, transient currents, and other current sensing purposes. Over the last two decades there have been significant developments related to current measurements using Rogowski-coil based systems. They have been in part related to innovations in design of the coils themselves with introduction of special materials, machining techniques [2], and various two- or three-dimensional printed circuit board structures [3]. The introduction of electronic devices for the load reduction, linearization and other error reducing techniques, device coding, parameter retention, digitization of output signals and communication to local data acquisition systems represents another area of developments [4]. Rogowski coils have a number of comparative advantages with respect to current transformers [5]. They are still considered to have, in general, somewhat less stringent accuracy requirements than current transformers. This view, however, may be justified only for current transformers of accuracy class better than 0.1. Rogowski coil applications in electric utilities have usually very demanding performance requirements. For example, when an extended operating current range required of Rogowski coils is taken into consideration, their linearity requirements get much closer to those of current transformers operating within their nominal current range. Additional requirements for long term stability, immunity to: external electromagnetic fields, temperature change, noise in the presence of small signal levels that represent the first derivative of the current being sensed, change of physical position with respect to the current conductor, etc. aggravate the situation. Having in mind that the calibration systems should have uncertainties at least four, and preferably ten times smaller that those of device under calibration makes calibrations and determination of uncertainties related to these calibrations of Rogowski coils challenging. This paper will discuss determination of uncertainties related to a calibration of Rogowski coils using digital sampling and current comparator based techniques. It will attempt to estimate the limits that are attainable by using these techniques for high-accuracy calibrations at national laboratories. References 1. W. Rogowski, W. Steinhaus, “Die Messung der magnetischen Spannung,” Arch. Electrotechn., I, 1912, pp.141-50. 2. J. D. Ramboz, “Machinable Rogowski Coil, Design, and Calibration,” IEEE Trans. Instr. Meas., Vol.45, No.2, June 2006, pp. 939 - 943. 3. C. Qing, L. Hong-bin, Z. Ming-ming, L. Yan-bin, “Desing and Characteristics of Two Rogowski Coils Based on Printed Circuit Board,”. IEEE Trans. Instr. Meas., Vol.55, No.3, Apr. 1996, pp. 511- 515. 4. D. Destefan, J. D. Ramboz, S. Weiss, “Rogowski Coil Based Systems to Support Utility and Power Industry Current Measurement Needs,”. National Conference of Standards Laboratories (NCSL) International 2007 Workshop and Symposium, 2007, Saint Paul, MN, 19 pp. 5. Lj. A. Kojovic, “Comparative Performance Characteristics of Current Transformers and Rogowski Coils used for Protective Relaying Purposes,” IEEE PES General Meeting, Tampa, FL, 2007. |
|
NCSL International © 1996-2008 All Content. September 05, 2008 12:27 PM |