Rogowski Coils

Rogowski coils are used for measuring alternating current.
They work by sensing magnetic field caused by the current without the need
to make an electrical contact with the conductor. These coils have been used in
various forms for detecting and measuring electrical currents for decades but it is
only in recent years that their potential is being realized on a commercial scale.

They operate on a simple principle. An 'air cored' coil is placed round the conductor
in a toroidal fashion so that the alternating magnetic field produced by the current
induces a voltage in the coil. The coil is effectively a mutual inductance coupled to the
conductor being measured and the voltage output is proportional to the rate of change
of current. To complete the transducer this voltage is integrated electronically to provide
an output that reproduces the current waveform. This combination of coil and integrator
provides a system where the output is independent of frequency, which has an accurate
phase response, and which can measure complex current waveforms.

The output from the integrator can be used with any form of electronic indicating device
such as a voltmeter, oscilloscope, protection system or metering equipment.
The coils are wound either on a flexible former that is subsequently wrapped round the
conductor to be measured or on a rigid toroidal former.

Rogowski Coils
Two forms of transducer coil have been developed. One is Rigid Toroid design which
can be used for high precision measurements and some forms of permanent installation.
This has an accuracy and stabilty comparible to a class AL current transformer but
without the current-range limitations.
A clip-on version of the rigid toroid can be produced with similar specifications.
The alternative form of the transducer is the Flexible Coil. This is less sensitive and
less accurate than the rigid form but is extremely compact and versatile.