With increasing requirements of online monitoring of Overhead Transmission Lines (OTL) in smart grids, contact-free measurement technologies have been updated these decades. However, the contactless sensors in past research are still limited to the application environment like wind deflection. This paper proposes an advanced detection approach with a novel structure to enhance the possibility of implementation and reduce cost. Three pairs of detection probes arranged in a curved pattern can collect differential voltage signals based on the principle of electric field radiation. With three-phase vector decomposition, the 9 unknown variables including voltage to be measured and status of lines (sag and wind deflection) in 9 equations can be constructed. The voltages to be measured can be calculated by solving this nonlinear equation system by iteration. Also, the position of the device installation is optimized by Particle Swarm Optimization (PSO) algorithm regarding accuracy. The whole measurement device can be easily implemented on the towers according to the distance of insulation requirement regardless of the position of lines. The simulation of level 110 kV is investigated and a model system is built to measure a lower-level voltage for verification. The results show that the proposed non-contact OTL voltage approach can reach the desired accuracy with low costs and monitor the status of lines.

The contact-free measurement of current and voltage technologies are key points to achieve online monitoring tasks in the modern power system, which are updated in these decades. However, ensuring accuracy and a convenient level of operation in the meanwhile is also a difficult task that needs to be solved in advance. Besides, there are unidealized situations in the process of application of existence measure methods. According to the principle of electric field radiation, this paper proposes a non-contact voltage measurement approach based on three pairs of dual-probes circle measurement structures to measure the voltage of transmission wire online. Compared with the other methods, firstly, in this proposed approach, the sensor structure is optimized to be simple, low-cost, and easy to install and operate. Secondly, the potential error in the measuring process caused by the other electric field in the environment is eliminated with dual probes, and the influence of unidealized situations like off-center wire can be also avoided by calculating algorithm. Third, in no matter DC (Direct Current)/AC (Alternating Current) monitoring scenarios, with the proposed structure and methodology, the accuracy can be ensured to reach the acceptance level (below 1.63 %) even when the core of the wire to be measured is in any position instead of in the center. In the final, the simulation results and circuit tests verify these advantages to encourage us to implement them in the realistic power system.

Magnetoelectric sensors based on piezoelectric/ferromagnetic composites have been investigated extensively due to their resonance-enhanced magnetoelectric coupling effect and high sensitivity for magnetic field, especially at resonant frequency. However, the sensitivity drops rapidly when the frequency drifts away from resonance, making it unsuitable for low frequency applications. Frequency modulation has been proposed as an effective method to up-convert the frequency of the desired signal into the mechanical resonance. In this work, we study the optimized amplitude and frequency of the modulation field, which improve the sensitivity at low frequency by two orders of magnitude without increasing the noise level. Magnetic field of 200 pT is detected at 10 Hz with a near-flat frequency response in the range of 1 - 100 Hz, showing promising potential for low frequency applications in smart grid and renewable energy.

For the application of high-frequency current detection in power systems, such as very fast transient current, lightning current, partial discharge pulse current, etc., current sensors with a quick response are indispensable. Here, we propose a high-frequency magnetoelectric current sensor, which consists of a PZT piezoelectric ceramic and Metglas amorphous alloy. The proposed sensor is designed to work under d₁₅ thickness-shear mode, with the resonant frequency around 1.029 MHz. Furthermore, the proposed sensor is fabricated as a high-frequency magnetoelectric current sensor. A comparative experiment is carried out between the tunnel magnetoresistance sensor and the magnetoelectric sensor, in the aspect of high-frequency current detection up to 3 MHz. Our experimental results demonstrate that the d₁₅ thickness-shear mode magnetoelectric sensor has great potential for high-frequency current detection in smart grids.

In order to improve the measurement accuracy of high impulse current, this paper presents the system composition, performance improvement and, traceability method of a 100kA impulse current measuring system. Since the scale factor of the measuring system can be determined by the product of the scale factor of the components such as the shunt and the digital recorder, a method of component quantity traceability is proposed. Based on a shunt with rated current of 100 kA, a stable measuring system is developed. In addition, a reference impulse current calibrator and a step current generator for traceability are developed, so that the impulse scale factor of the shunt considering skin effect can be accurately calibrated. A single influence quantity independent quantification method was proposed. The influence of measurement error of 100kA impulse current measuring system is analyzed quantitatively. Based on the high current test results and theoretical analysis, the measurement uncertainty components of peak current and time parameters are evaluated. The expanded uncertainty of the scale factor and time parameters were 0.4% ( k = 2) and 0.8% ( k = 2) respectively. Evaluation results demonstrate that the developed measuring system can accurately reproduce and measure the high exponential lightning impulse current.

The load current of the new power system has significant characteristics on a wide dynamic range, which poses challenges to current sensing technologies. This paper proposes a magnetic-sensitive element based on NdFeB/Lead Zirconate Titanate (PZT) magnetoelectric composite materials, and further develops a magnetoelectric coupling current sensor. The sensor operates in torque mode, enabling the detection of both wide dynamic range alternating currents and weak alternating currents. Experimental studies show that the sensor achieved a power-frequency current detection sensitivity of 15.56 mV/A, a linear range of (0–120) A, and a detection limit of 153 μA. The results indicate that the sensor exhibits high sensitivity in alternating current (AC) current detection, and at power frequency, possesses both a wide dynamic range and the capability to detect weak currents. Therefore, it shows great application potential in scenarios such as wide dynamic range AC current measurement and weak current detection in power systems.