Accurate Rogowski coil sensors
March 2010
Electrical Power & Protection
LEM has introduced the first of its AC current sensor families based on Perfect Loop Technology. After calibration, the new RT series achieves absolute accuracy of better than 0,65% – including position error – making them the first split-core Rogowski coils to be suitable for use in Class 1 power devices.
An imperfect coil structure induces an unbalanced geometry and increases sensitivity to the position of the measured conductor within the sensor, or to the proximity of external electric cables. The RT series of sensors overcomes the problem of asymmetry resulting from the discontinuity at the sensor opening, which is inherent in conventional split-core Rogowski coils. LEM engineers have invented a unique magnetic coupling technology that allows a perfect extension of the magnetic flux at the loop opening, which compensates for coil asymmetry.
The thin, light and flexible format of the RT sensors allows them to fit into applications in which traditional current transformers are typically too heavy and bulky, especially when measuring high currents. Their split-core construction allows them to be easily wrapped around the conductor without dismantling cables or shutting down operation. The benchmark accuracy of RT series sensors provides enhanced performance in current and power monitors as well as energy meters.
The 5 mm gauge RT sensors are currently available with sensing apertures with diameters of 55 or 125 mm and are supplied with a five-year guarantee.
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