Product category: Sensors and Data Acquisition
News Release from: Power Electronic Measurements | Subject: RCTi Rogowski current transducer
Edited by the Electronicstalk Editorial Team on 7 March 2007
Transducer gets the
measure of interference
Rogowski current transducer measures small high-frequency interference currents, or low-strength higher-order harmonics in the presence of a large fundamental current
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A commonly encountered electrical engineering problem is the measurement of small high-frequency interference currents, or low-strength higher-order harmonics in the presence of a large fundamental current. However, the RCTi Rogowski current transducer from Power Electronic Measurements (PEM) has been successfully used to solve these and other typical problems in the power control and traction industries.
Traditionally in current measurement, the primary transducer (often a CT or hall effect device) has to be of sufficient size not to be saturated by the fundamental component.
This adds bulk which makes it more expensive, and in combination with the power analyser or oscilloscope, cannot provide the resolution to accurately measure small high-frequency currents.
The RCTi Rogowski transducer offers an economic solution with the coil sise specified independently of the measured current.
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The Rogowski coil does not suffer from magnetic saturation and cannot be affected or damaged by the fundamental current component.
In addition, tuning the RCTi bandwidth is a simple procedure, which attenuates the fundamental components, enhancing sensitivity to provide a larger signal-to-noise ratio at the frequencies of interest.
The RCTi also has a sufficiently high (-3dB) cutoff to measure accurately into the hundreds of kilohertz range.
Successful applications by PEM in the traction industry have included a European rail customer where the RCTi transducer was used to monitor the motor drive harmonics interfering with the pantograph.
In addition it has been applied to facilitate EMC assessment for a new national railway in the Far East where the railway signalling system passed coded messages between a trackside cable and the train antenna at tens of kilohertz.
The EMC issue concerned the traction harmonic currents in the third rail and running rails which can couple inductively into the signalling cable causing interference at the antenna.
To provide a certain signal-to-noise ratio for transmitted data, an optimised RCTi transducer was used.
This is flexible and can be easily secured around the rail track.
The low-frequency cutoff is optimised at 4.2kHz with a flat response at 10kHz but -40dB of attenuation at 1kHz.
The RCTi effectively measure small interference currents in the rail of the order of a few milliamps at tens of kilohertz, yet rejecting much larger components (of the order of amperes) from power frequency sources.
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