Understanding the Unique Wiring of Rogowski Coils
The Rogowski coil, named after inventor Walter Rogowski, serves as a vital electrical instrument designed for measuring alternating current (AC) or high-speed current pulses. Unlike traditional methods, this coil takes the form of a toroid, featuring a helical coil of wire with a lead that traverses from one end to the center, ultimately returning to the other end. This unique configuration, known as per-lesion Rogowski, ensures both terminals are conveniently located at the same end of the coil.
Functionally, the Rogowski Coil operates as an ‘air-cored’ toroidal coil strategically positioned around a conductor. As the current generates an alternating magnetic field, it induces a voltage in the coil proportionate to the rate of change of the current. The direct output formula is Vout = M dI/dt, where ‘M’ denotes the mutual inductance of the coil, and ‘dI/dt’ signifies the rate of current change. To refine the transducer’s output, the voltages undergo electronic integration. This process ensures that the integrated output accurately reproduces the current waveform. The Rogowski coil stands as a sophisticated and efficient tool in the realm of electrical measurements, offering precision and reliability in capturing and interpreting alternating currents and high-speed pulses.
- Due to its low inductance, it can respond to rapidly changing currents up to several nanoseconds.
- It has no iron core to saturate, making it highly linear even when subjected to large currents, such as those used in electrical power transmission, welding, or pulsed power applications.
- This linearity also enables a high-current Rogowski coil to be calibrated using very small reference currents.
- No danger of secondary winding opening.
Coil and Integrator
The synergy between the coil and integrator results in an exceptionally versatile current measurement system, accommodating diverse frequencies, current levels, and conductor sizes while maintaining independence from frequency variations. With an accurate step response, it adeptly captures complex current waveforms and transients.
Linearity
The fundamental characteristic that sets the Rogowski coil measurement system apart is its inherent linearity. Unlike other systems, the coil lacks saturable components, ensuring that the output current increases in a linear fashion, directly proportional to the operating limit set by voltage breakdown. This linear behavior simplifies the calibration process for Rogowski coils, as transducers can be calibrated at any convenient current level, ensuring accuracy across all current ranges, even for substantial ones. Additionally, the integrator maintains inherent linearity until the electronics reach saturation. This linearity grants the transducers an extensive dynamic range and exceptional transient response, further enhancing their versatility and performance.
Coil Winding
With a Rogowski coil, it is important to ensure that the windings are as uniform as possible. A non-uniform winding makes the coil sensitive to magnetic pickup from adjacent conductors or other sources of magnetic field. We have developed our technology to ensure precise winding. Coils come in many styles including rigid and flexible coils, we have developed variations to meet specific needs.
Output Indication
The output from the integrator is typically a voltage waveform that reproduces the current waveform. It can be used with any type of electronic signal instrument having an input impedance greater than approximately 5kOhm such as voltmeters, oscilloscopes, transient recorders, or security systems. Other outputs are also available such as DC voltage representing RMS output, 4 – 20 mA DC output, etc.
Split Coils
Some designs of the coil can be fitted onto a conductor without the need to disconnect the conductor. Most flexible coils can be fitted in this way and it is also possible to manufacture split rigid coils. Split iron-core devices such as current transformers are subject to appreciable amplitude and phase errors if the halves are misaligned by even the slightest amount. Rogowski coils do not have this problem. Misalignment of the joining faces of the divided Rogowski coil has only a small effect on amplitude and no effect on phase.