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How does the Rogowski Coil Work?
Similar to AC current transformers in how the voltage is induced in a secondary coil and that its proportional to the current flow within the conductor.
The difference between Rogowski coils and AC current transformers is in the core. The main difference between an AC current transformer and a Rogowski coil is the air core is used in a Rogowski coil, whereas in a CT a steel core is used.
When current passes through the conductor, it will create a magnetic field is created when current passes through the inductor and as a result of the intersection with a magnetic field, the voltage is induced between the terminals of a Rogowski coil.
What is a Rogowski Coil?
Rogowski Coils are electrical devices used for measuring alternating AC current. The Rogowski Coil is named after the German physicist Walter Rogowski. Output signals from a Rogowski CT is fed to transducers used for measuring which then give standardised AC current of max. 1 A at the output. Rogowski Current Transformers are flexible and measures current for power metering and analysis of power quality. They are ideal solutions when space is limited and when needing a rope-style CT to physically wrap around a irregular shaped conductor or wire.
They are used for current measurement of AC currents. Mostly for retrospective installation in existing systems but often on power rails or power cables. Rogowski coils separate making installation around the primary conductor is possible. The output signal coil and fed to a measurement transducer. The Rope CT has flexible sensor coils that wrap easily around the conductor carrying the current. A Rogowski can measure up to a couple thousand amperes of large currents without increasing transducer size.
An important property of the Rogowski coil is that it is inherently linear. As the coil does not contain saturable components. Also the output increases linearly in proportion to the current up to the operating limit determined by voltage breakdown. Rogowski coils are easy to calibrate due to linearity as transducers can be calibrated at any convenient current level. The calibration will be accurate for all currents including very large ones. Also, because of the Rogowski Coils linearity, the transducers have a broad dynamic range and great transient responses.
Flexibility –They have a flexible lightweight clip-around sensor coil that is easy to wrap around a current-carrying conductor. Making them easily inserted into components that are hard to reach in a circuit.
Lower cost – The Rogowski coil is usually cheaper than a hall effect sensor or transformer.
Non-intrusive or lossless measurement — The Rogowski coil has a fast signal response and very linear signal voltage due to drawing very little current from the DUT by low insertion impedance.
AC Current Only – Rogowski Coils will not handle DC current. Only AC.
Sensitivity – Compared to a current transformer the Rogowski coil has a lower sensitivity from not having a high permeability magnetic core.
Alike an AC current transformer the Rogowski coil has a voltage induced into a secondary coil which is proportional to the current flow through an isolated conductor. Although, Rogowski coils can measure large currents without saturation due to its “air” core that is non-magnetic. The air core is designed to enable a faster signal response and a very linear signal voltage by having a lower insertion impedance. Compared to the hall effect sensor/current transformer the Rogowski coil is very cost effective. Making Rogowski coils the most ideal measuring tool for up to thousands of amperes of AC current.
Three Phase Rogowski Coils
The RCS-5A is an example of a three phase rogowski coil set. Its alternative to standard 5A current transformers and offers the ability to choose from several different amp input ratings, allowing flexibility in working fields.
- Rated input from 500, 1000, 2500, and 5000 amps
- Output of 5A (Three Phase Set)
- Linearity 0.5%
- Overall Accuracy 1.0%
- Custom diameters, and other parameters are available
- UL Listed