what's rogowski coils

Rogowski coil (Rogowski Coil), also known as a current measuring coil and a differential current sensor, is a toroidal coil evenly wound around a non-ferromagnetic material. The signal it outputs is the differential of the current with respect to time. Through a circuit that integrates the output voltage signal, the input current can be restored.

The theoretical basis for Rogowski coil to measure current is Faraday's law of electromagnetic induction and Ampère's circuital law. When the measured current passes through the center of the Rogowski coil along the axis, a corresponding changing magnetic field will be generated within the volume surrounded by the annular winding. When its cross-section is rectangular, the mutual inductance coefficient m and the self-inductance coefficient l are respectively: m = μ0nhln(b/a)/2π, l = μ0n^2hln(b/a)/2π (where h is the magnetic field strength inside the coil, b is the magnetic induction intensity inside the coil, μ0 is the vacuum permeability, n is the number of coil turns, a and b are the inner and outer diameters of the cross-section of the coil respectively, and h is the cross-sectional height).

It can be seen that when the coil is fixed, m is a constant value, and the output voltage of the coil is proportional to di/dt, that is to say, the output voltage of the Rogowski coil is proportional to the differential of the measured current.

Rogowski coil has the following characteristics:

• Suitable for current testing ranging from milliamperes to megaamperes;

• Has good linearity;

• Large bandwidth range;

• No risk of secondary open circuit;

• Strong overcurrent ability;

• Low power consumption;

• Can measure irregular conductors;

• Easy to install without damaging the conductor;

• Light weight.

Rogowski coils are often used in fields such as power systems, electronic equipment, and laboratories to measure and monitor current. For example, in semiconductor switch waveform measurement, large alternating current measurement in generator/motor drives and power supplies, pulsed power applications, high-frequency sinusoidal wave applications (such as induction heating), lightning strike measurement, and measurement of small alternating current in the case of large direct current (such as capacitor ripple), etc.

In actual use, in addition to the fixed and known frequency standard sine wave, the Rogowski coil needs to be used in conjunction with an integrator to restore the voltage signal proportional to the input primary current. In order to reduce the influence of interference, an integrator with digital output is preferred, and it should be noted that the analog connection between the integrator and the Rogowski coil should be as short as possible and a shielded wire should be used as much as possible.