Rogowskikierre

Rogowskikierre, or Rogowski coil, is an electrical measuring device used to determine alternating currents without a magnetic core. It consists of a flexible, insulated conductor wound into many turns around a non-magnetic form and placed around the conductor whose current is to be measured. The coil is typically made in a flat or curved strip that can be clipped around a busbar or cable.

Principle of operation: The Rogowskikierre senses the time rate of change of the current in the conductor. The induced voltage in the coil is proportional to the derivative di/dt of the current, with a proportionality factor determined by the mutual inductance between the coil and the conductor. To obtain the actual current waveform, the coil’s output is passed through an electronic integrator or calibrated to yield current values.

Construction and use: The coil is an air-core device, which means it has no ferromagnetic material and therefore avoids saturation and hysteresis effects. It is praised for its wide bandwidth, safety, and flexibility, allowing it to be placed around live conductors without interrupting the circuit. Proper installation, shielding, and a stable, well-calibrated integration stage are required for accurate measurements.

Advantages and limitations: Advantages include high current capability, broad frequency range, no core saturation, and non-contact measurement. Limitations include inability to sense steady direct currents, dependence on a stable integration circuit, sensitivity to offset drift and noise, and the need for precise calibration for converting output voltage to current.

Applications: Used in power systems, protection relays, laboratory current measurements, and testing of high-current or pulsed systems where a non-intrusive, wide-band sensor is advantageous. See also current sensor and current transformer.