|
A Rogowski coil, named after Walter Rogowski, is an electrical device for measuring alternating current (AC) or high speed current pulses. It consists of a helical coil of wire with the lead from one end returning through the centre of the coil to the other end, so that both terminals are at the same end of the coil. The whole assembly is then wrapped around the straight conductor whose current is to be measured. There is no metal (iron) core. The winding density, the diameter of the coil and the rigidity of the winding are critical for preserving immunity to external fields and low sensitivity to the positioning of the measured conductor.〔John G. Webster, Halit Eren (ed.), ''Measurement, Instrumentation, and Sensors Handbook, Second Edition: Electromagnetic, Optical, Radiation, Chemical, and Biomedical Measurement'', CRC Press, 2014, ISBN 1-439-84891-2, pp. 16-6 to 16-7. 〕〔Klaus Schon, ''High Impulse Voltage and Current Measurement Techniques: Fundamentals – Measuring Instruments – Measuring Methods'', Springer Science & Business Media, 2013, ISBN 3-319-00378-X, p. 193.〕 Since the voltage that is induced in the coil is proportional to the rate of change (derivative) of current in the straight conductor, the output of the Rogowski coil is usually connected to an electrical (or electronic) integrator circuit to provide an output signal that is proportional to the current. Single-chip signal processors with built-in analog to digital converters are often used for this purpose.〔 ==Advantages== This type of coil has advantages over other types of current transformers. * It is not a closed loop, because the second terminal is passed back through the center of the toroid core (commonly a plastic or rubber tube) and connected along the first terminal. This allows the coil to be open-ended and flexible, allowing it to be wrapped around a live conductor without disturbing it. However, positioning of the measured conductor is important in that case: It has been shown that, with flexible sensors, the effect of the position on the accuracy ranges from 1 to 3%. Another technique uses two rigid winding halves with a precise locking mechanism.〔 * Due to its low inductance, it can respond to fast-changing currents, down to several nanoseconds.〔Slawomir Tumanski, ''Handbook of Magnetic Measurements'', CRC Press, 2011, ISBN 1-439-82952-7, p. 175.〕 * Because it has no iron core to saturate, it is highly linear even when subjected to large currents, such as those used in electric power transmission, welding, or pulsed power applications.〔 This linearity also enables a high-current Rogowski coil to be calibrated using much smaller reference currents.〔 * No danger of opening the secondary winding.〔 * Lower construction costs.〔 * Temperature compensation is simple.〔 * Conventional current transformers require an increase of the number of secondary turns, in order to keep the output current constant. Therefore, a Rogowski coil for large current is smaller than an equivalent rating current transformer.〔Stephen A. Dyer, ''Wiley Survey of Instrumentation and Measurement'', John Wiley & Sons, 2004, ISBN 0-471-22165-1, p. 265.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rogowski coil」の詳細全文を読む スポンサード リンク
|