Curved Trapezoidal Magnetic Flux Concentrator Design for Current Measurement of Multi-Core Power Cable With Magnetic Sensing

Abstract

Operating current of a multi-core power cable can be monitored by sensing the magnetic fields around the cable surface. Magnetic flux concentrators (MFCs) are typically installed to collect the magnetic flux lines and amplify the magnetic field signals for magnetic sensors that are sandwiched by pairs of MFCs. However, installing a series of conventional planar MFCs around the circular cable surface would form a polygonal structure, adversely aggregating the magnetic flux lines at the corners of the polygon. In this paper, a curved MFC structure was developed to overcome the problem. First, a simple curved structure (i.e., curved strip-shaped MFCs) was derived to accommodate magnetic sensors around the cable surface. Then, it was modified into the trapezoidal shape for further improving the amplification ratio after studying the influence of MFC thickness, aspect ratio, and end-to-end ratio. The saturation effect and frequency response of MFCs were also studied. The effectiveness of the curved trapezoidal MFCs compared to the strip-shaped ones was validated experimentally, in which the average amplification ratio of the trapezoidal MFCs (5.12) was substantially larger than that of the strip-shaped MFCs (1.46). The curved trapezoidal MFCs not only eliminate the magnetic field aggregation at the polygon corners but also fit compactly the round geometry of the cable compactly. More importantly, enhancing the magnetic field signals for the magnetic sensors can potentially improve the system ability to sense the weak magnetic field variations from slight current changes. The high-order harmonics can also be potentially restored because the curved trapezoidal MFCs have a good frequency response.