City Research Online

Mathematical Modelling and Design of Current Sensors in Non-Conventional Instrument Transformers

Nikolic, B. (2023). Mathematical Modelling and Design of Current Sensors in Non-Conventional Instrument Transformers. (Unpublished Doctoral thesis, City, University of London)


This research brings a novel approach for current measurement using magnetic shape memory (MSM) smart alloys. The non-conventional instrument transformer (NCIT) proposed in this research uses the property of these alloys that their shape changes when exposed to a magnetic field.

It has been shown that it is possible to measure alternating currents (a.c.) in high voltage overhead transmission lines by correlating the magnetic field produced by the current to shape changes in an MSM-based sensor. Methodologies for finite element modelling of the proposed NCIT have been developed. The developed methodology and obtained results are validated by comparing them to the results obtained through an experiment done by a manufacturer of MSM materials.

5M Ni-Mn-Ga MSM crystals with Type I twin boundaries and a load of 0.5 N/mm2 were identified as the most suitable type of MSM materials for this application. The combination of a very long fatigue life, with relatively low twinning stress, makes them the most prospective for use in MSM-based current sensors.

The main characteristics of overhead transmission lines are described as well as the types of conductors typically used. This analysis brought us to the conclusion that special attention in this research should be given to ACSR and AAAC conductors, more specifically to 528-Al1/69- ST1A conductor (old code MOOSE) and 996-AL5 (old code REDWOOD). Additionally, the latest trends in the development of overhead transmission lines are discussed, as well as international standards which are relevant to these types of lines.

These conductors were modelled in finite element (FE) package ANSYS APDL, together with the MSM element and the magnetic circuit, and included into a single finite element model. This approach allows us to take into account significant changes that take place within an MSM element during its elongation. Based on this, we were able to determine both the bottom and upper limits of the measurement range, optimise the NCIT for transmission lines, and propose several designs of the NCIT. Finally, this allowed relating the current inside the conductor to the voltage at the output of the LVDT.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QA Mathematics
T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Nikolic Thesis 2023 PDF-A.pdf]
Text - Accepted Version
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