What is the disadvantage of Rogowski coil?

Accurate current measurement is critical for many applications, from industrial process control to smart homes. There are several ways to measure current, but each has advantages and disadvantages. One of the less common types of current sensors is the Rogowski coil, however, I also find it one of the most interesting.

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A Rogowski coil is a current transformer that measures alternating current in electrical systems. It consists of a flexible coil of wire wrapped around a current-carrying conductor and produces an output voltage proportional to the rate of change of current. This method makes it an ideal option for measuring high-frequency currents, typically having a response from tens of kilohertz to a megahertz or more. 

One of the key features of the Rogowski coil is its wide frequency range and fast response. As the output voltage is proportional to the rate of change of current, a Rogowski coil can accurately measure high-frequency currents without sacrificing accuracy. In addition, because the coil is flexible and does not have a ferromagnetic core, it does not have the inductive reactance present in other current sensors. Due to this low inductance, the coil does not introduce significant phase shifts or other errors into the current measurement. As a result, it can also respond quickly to changes in current, making it suitable for use in dynamic systems such as precision current control loops or safety protection. 

In addition to its wide frequency response and low inductance, the Rogowski coil also has high linearity. The coil's linearity means that the output voltage is directly proportional to the rate of current change. 

Despite the advantages, the disadvantages of a Rogowski coil also need to be considered. Flexible Rogowski coils can be more challenging to install and calibrate than other current sensors because they need to be carefully wrapped around the wire for accurate measurement. However, this can also be an advantage, as the Rogowski coil does not need to make a complete loop, so the current sense coil can be inserted into an existing installation. Not all Rogowski coils are flexible; for example, I have several from Pulse Electronics, which are supplied in a hard plastic housing.

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Another disadvantage of the Rogowski coil is that it is more sensitive to external electromagnetic fields than other current sensors. Because it does not have a ferromagnetic core, it can be affected by external magnetic fields, which can cause measurement errors. This susceptibility to electromagnetic fields may require the coil to be shielded to make accurate measurements.

The most commonly stated disadvantage of a Rogwoski coil is the need for an external integrator. As a result, the coil cannot be used without some external components. However, there are single-chip integrator options, and pre-packaged coils such as the ones I have include the integrator inside the component body, making them extremely easy to use.

The Rogowski coil is a valuable tool for measuring AC currents in various applications. Its wide frequency range, low inductance, high linearity, and fast response time make it an ideal choice for many applications. However, its complexity and sensitivity to external electromagnetic fields must be considered when deciding if it is the right choice for a particular application.

Articles and Papers

This page collects together both relevant and historical literature about the working of Rogowski coils and associated equipment.

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