Magnetic sensor have been widely used for current measurement in diverse industries. In order to achieve a large current measurement without an iron core structure, magnetic sensors are often arranged to be a circular array for designing a new electronic current transformer (ECT). However, this ECT with a circular array of magnetic sensors usually suffers from tradeoffs between the number of sensors and measurement accuracy. This paper visualizes this tradeoff and proposes a 3-D magnetic-field model to analyze the impact of the magnetic sensor circular array position on current measurement. We develop an analytical expression of the current measurement errors to estimate the minimum number of required magnetic sensors and point out the acceptable deviations of ECT position under various accuracy classes. Based on the estimation results, we design a new circular array with eight magnetic sensors and build a three-phase current measurement system. The test results demonstrate the efficiency and robustness of the designed class-1.0 ECT, which successfully keeps accuracy class 1.0 under various position deviations in balanced or unbalanced three-phase power delivery systems.

Overhead and underground power line monitoring is an essential infrastructure for advanced operation in the smart grid. Wireless sensor networks are attractive to remote power line monitoring, due to their rare geography restrictions, simple engineering design, and flexible equipment expansion. Considering the ZigBee's characteristic of low transmission rate, almost commercial sensors adopt the high-speed communication, such as Cellular and WiFi, to implement the real-time wireless monitoring. However, among all wireless technologies, ZigBee, characterizing high security, ultra-low power consumption, reliable network, low cost, and ease of design, is widely used in many industries. This paper proposes a new ZigBee-based communication for multifunctional electronic current transformers (ECTs), which are used in overhead and underground line monitoring. To tackle ZigBee's low transmission rate, the proposed method involving a transmission strategy can make the ZigBee-based communication satisfy both measurable and protective purposes of multifunctional ECTs. Finally, the new ZigBee-based wireless communication is implemented and integrated with an ECT, which is based on the coreless Hall-effect current transformer (HCT), and the proposed ZigBee-based wireless multifunctional HCT is called ZiHCT. The measurement results show that the ZiHCT can achieve accuracy not only to Class 0.5 for measuring CTs, but also to Class 5P20 for protective CTs according to IEC standard 60044-8.

Traditional current monitoring devices (e.g. current transformers) for transmission and distribution (T&D) networks are mostly installed at substations, so real-time and accurate information on current is almost unavailable for on-site load current monitoring, imbalance assessment, and equipment maintenance. This increases the fault risk in T&D networks and degrades the reliability and quality of the power supply. To address such a situation, this study proposes an intelligent and contactless current measurement method. The proposed method uses only a small number of magnetic-field sensors and the conductor geometry specification of an overhead line obtained from utilities. The simulation results show that the proposed method can accurately calculate each phase current using only three magnetic field sensors. In addition, a scaled-down overhead line measurement system was built to test the proposed method. The experimental results verify the feasibility of the proposed contactless method for overhead-line current measurement with less than 10% maximum measurement error.

The measurement of harmonic voltage distortions in medium and high voltage systems is always regarded as a challenging task. For transmission systems, the widely used capacitor voltage transformers offer inadequate frequency responses for harmonic measurement. For distribution systems, voltage transformers are only available in limited locations. In order to provide a convenient and efficient solution for the situations above, this paper proposes a contactless method to measure voltage distortions. A small number of electric field sensors are used with partial knowledge of conductor geometry information of overhead lines. In addition, the method focuses on estimating the percentage harmonic voltage levels instead of the actual harmonic voltage values, which leads to a robust and simple measurement scheme. The proposed method has been validated by numerical simulations and experimental tests on a reduced scale model of an overhead transmission line.

Measuring the current in high-voltage direct current (HVDC) systems is always regarded as a challenging task. For transmission systems, DC current transformers or sensors are only available in substations and converter stations. In order to provide more flexibility and convenience, this paper proposes a contactless DC current sensor, which can be easily placed on-site in the environment of HVDC overhead transmission lines. The proposed method significantly improves the convenience and safety of the HVDC current measurement. Using a magnetic-field sensor array, the proposed current algorithm can optimally calculate the overhead-line currents with partially known overhead-line geometry. The simulation results in this paper demonstrate that the proposed method can accurately calculate the HVDC current. Moreover, the proposed method is validated by a reduced-scale HVDC overhead transmission line.