Novel Coreless Current Sensing Systems-Design, Development and Evaluation

Abstract

Current and voltage are the two essential parameters that are frequently sensed and monitored in electrical systems like the electric power distribution systems and the condition monitoring systems, say, for large machines and ships. The tremendous advancement in the field of Internet of Things (IoT) has granted seamless access to important parameters of a system, covering a wide geographical area, such as the automatic meter reading or protection systems in a power system with the sensing nodes placed at remote locations. Also, the recent progress in data science has provided ways to effectively capture valuable information from such measured data. To realize such applications, simple, low-cost current and voltage sensors with sufficient accuracy and reliability are required. Also, they should be easy to install and maintain. Conventionally, alternating current is measured using current transformers (CTs). They are widely used for measurement and protection applications. CTs are bulky, expensive, and the output is affected due to the non-idealities of its magnetic core. Another approach, which is relatively new, involves core-less current sensors that employ highly sensitive semi-conductor based magnetic sensing elements. They have many advantages over CTs. The proposed thesis deals with the development and evaluation of new methods or schemes to improve the performance of the existing core-less current sensors.
The design and development of new non-contact and core-less current sensors/probes, that require limited access to the current carrying conductor, are presented in this research work. Since they require only limited access, they open up new applications such as measurement of current in a conductor concealed in a wall or current in a Printed Circuit Board (PCB) track. Another novel feature of the developed current sensors is that their outputs are not sensitive to the variation in the gap between the wire and sensing elements of the probe, which is a major advantage as this helps to provide reliable measurement for a long time. Furthermore, a modified version of the differential current probe, in which the sensing elements are kept on both sides of the conductor, is also presented in this thesis. This modified differential current probe significantly reduces the effect of vertical and horizontal misalignments between the conductor and the sensing elements in the output. Thus, it helps to provide precise and accurate measurement of current.
The existing core-less current sensors based on Ampere’s circuital law need 360º access to the current carrying conductor. This approach has low sensitivity to the external magnetic field, but the output is sensitive to the misalignment between the sensing element and the conductor, deviation from the circular shape of the sensor array, etc. In this work, a detailed theoretical and experimental analysis has been conducted to evaluate the contribution of each of the misalignment parameters in the final output. This study will help the engineers focus on the relevant aspects required to keep the error due to the misalignments within the desired limits. Additionally, a simple and less expensive calibration system to test and verify the current sensor, say, the conventional CT, has been designed and realized. Suitable prototypes of the sensors/probes and the calibration system have been developed and tested in the laboratory to validate their functionality and performance.