Studie av implementering av Rogowski-spolar för växelströmsmätning i ABB:s optiska strömgivare

Sammanfattning: ABB HVDC is a manufacturer of optical current transducers (OCTs) are used which are used to measure alternating currents in high voltage applications. The sensor used today is based on a current transformer and measures alternating currents between 100 and 4000 A. With the current transformer there are disadvantages due to its core of magnetic material which saturates at high currents. As the core goes into saturation, the number of different variants of current transducers increases re-garding rated currents, measurement requirements and behavior in short-circuit currents and transients. Due to such a limitation, there is the need for an alternative solution. The Rogowski coil is just like the current transformer based on Faraday's law of in-duction. Instead of several different variants, a solution with Rogowski coils can be varied with different measuring ranges of the sensor electronics. Therefore, the possibility of implementing a Rogowski coil in an OCT is being investigated. An OCT consists partly of the sensor itself but also an electronics unit and an optical in-terface unit (OIU). Since the signal from a Rogowski coil is proportional to the derivative of the current in the measurement object, a type of integrator is needed to recreate the signal. The possibility of having either an analog or digital integrator exists, but a digital can bring benefits such as reduced delivery time. By utilizing existing circuits on the OIU, a digital integrator could be implemented. In the work, an integrator function has been created in Matlab to recreate the signal. A scale factor was determined to minimize the amplitude difference between reference sensors and the Rogowski sig-nal. The work shows that current measurement with the Rogowski coil where the fre-quency is varied results in an amplitude difference between the reference sensor and the Rogowski coil. The amplitude difference has a linear trend and could be offset by a frequency coefficient. The work also discusses proposals for further tests that should be performed to identify how different factors affect a current measurement.