what is called Rogowski coil

First, what is called Rogowski coil

 The Rogowski coil is a toroidal coil that is evenly wound around a non-ferromagnetic material. The output signal is the differential of current versus time. The input current can be truly restored by a circuit that integrates the output voltage signal. The coil has the characteristics of real-time measurement of current, fast response and no saturation, and is suitable for AC, especially high-frequency and high-current measurement.

Rogowski coils (Rogowski coils) are also called current measuring coils and differential current sensors, which are mainly used to measure AC current. The working principle of the Rogowski coil is that the coil bobbin surrounds the conductor to be tested, and the magnetic field around the conductor changes with the current in the conductor. The enameled wire on the skeleton induces an electromotive force. According to mathematical derivation, the electromotive force is proportional to the derivative of the current in the conductor, and the proportional coefficient is related to the number of turns of the coil, the cross-section of the skeleton, the magnetic permeability, and the like, and the electric current in the conductor can be restored by integrating the electromotive force. A complete Rogowski coil current measurement system should include a coil and an integrator. Let's take a look at the coil and integrator to give you a detailed understanding of how Roche's coil works.

Second, Roche coil working principle
 
The Rogowski coil is a hollow-annular coil that is flexible and rigid and can be placed directly on the conductor to be measured to measure AC current. The basic principles of its design are shown in the figure above:

The theoretical basis for measuring the current of the Rogowski coil is Faraday's law of electromagnetic induction and the ampere-loop law. When the measured current passes through the center of the Rogowski coil along the axis, a correspondingly changing magnetic field is generated in the volume enclosed by the toroidal winding, and the intensity is H. The loop law is:

∮H·dl=I(t)
From B=μH, e(t)=dΦ/dt, Ф=N∫B·dS, e(t)=M·di/dt,
When the cross section is rectangular, the mutual inductance M and the self-inductance coefficient L are respectively:
M=μ0Nhln(b/a)/2π
L=μ0N^2hln(b/a)/2π

In the above formula, H is the magnetic field strength inside the coil, B is the magnetic induction intensity inside the coil, μ is the vacuum permeability, N is the number of turns of the coil, and e(t) is the induced voltage a and b at both ends of the coil. The inner and outer diameter of the section, h is the height of the section. It can be seen that when the coil is fixed, M is a fixed value, and the output voltage of the coil is proportional to di/dt.

For more information,please contact us at sales@xfullstar.com