What is the purpose and construction of a Rogowski coil in high current measurement applications?

A Rogowski coil is an electrical device used to measure alternating current (AC) or high-speed current pulses. It is particularly well-suited for high current measurement applications where traditional current transformers (CTs) might saturate or be impractical to install. The purpose of a Rogowski coil is to provide an accurate and non-intrusive measurement of current flowing through a conductor, without the risk of saturation or the need for a direct electrical connection. Its construction is relatively simple. It consists of a helical coil of wire wound on a non-magnetic core (often air). The coil is typically flexible, allowing it to be easily wrapped around the current-carrying conductor. The coil's two ends are connected to an integrator circuit. The integrator circuit is essential because the output voltage of the Rogowski coil is proportional to the rate of change of the current (di/dt), not the current itself. The integrator converts this signal into a voltage proportional to the current. When the Rogowski coil is placed around a conductor carrying AC current, the changing magnetic field produced by the current induces a voltage in the coil. This induced voltage is proportional to the rate of change of the current. The integrator circuit then processes this voltage to produce an output voltage that is proportional to the actual current flowing through the conductor. Rogowski coils offer several advantages over traditional CTs. They do not saturate, even at very high currents. They are lightweight and flexible, making them easy to install in tight spaces. They can measure a wide range of frequencies, from very low frequencies (e.g., 50/60 Hz) to high frequencies (e.g., kHz or MHz). They provide electrical isolation between the current-carrying conductor and the measurement circuit. However, they also have some disadvantages. They require an integrator circuit, which adds complexity and cost to the measurement system. They are more susceptible to noise than CTs. They may require calibration to ensure accuracy. Despite these limitations, Rogowski coils are widely used in high current measurement applications, such as power system monitoring, welding equipment, and motor drives, due to their accuracy, flexibility, and immunity to saturation.