Power Current Transformer Research Articles

Parameter Design of a Self-Generated Power Current Transformer of an Intelligent Miniature Circuit Breaker Based on COMSOL

With the deep penetration of renewable energy and power electronic equipment, the overcurrent protection of an intelligent miniature circuit breaker faces new challenges. The electronic controller of an intelligent miniature circuit breaker is typically powered by the bus current rather than the phase voltage to ensure a robust overcurrent protection response under all conditions, including severe short-circuit faults. So, the performance of the current transformer serving as an energy harvesting unit and the corresponding direct current to direct current convention circuit is one of the critical issues due to the limited volume of an intelligent miniature circuit breaker. In this research, a finite element model of a current transformer for an intelligent miniature circuit breaker is constructed by COMSOL to evaluate the impact of the core material, the core size, and the number of coil turns on the energy harvesting capability of the current transformer. Meanwhile, the relationship between the output of the power supply and its design parameters is investigated by circuit simulation. As a result, a novel type of current transformer is proposed based on well-designed parameters. Finally, experimental tests have been conducted to verify the hysteresis characteristics, output characteristics, and energy harvesting effect. The results demonstrate that the hysteresis properties of the transformer align with the simulation results. The power supply can work with a minimum current of 8 amperes, which is 23.08% better than before.

Transforming characteristics of the Rogowski coil current transformer with a digital integrator for high‐frequency signals

The Rogowski coil current transformer is widely used in intelligent substations for its rapid response, wide bandwidth measurement, and non-magnetic saturation. In most cases, it works with a digital integrator to restore the differential signal output by the coil. However, its output waveform can be deformed when transforming high-frequency signals generated in the transient process of the power system. The working process of the Rogowski coil current transformer is presented, including Rogowski coil head transferring, analogue filter filtering, analogue-to-digital converter sampling, and digital integrator restoring. The reason for the waveform deformation when transforming high-frequency signals is investigated by theoretical derivation. In order to show the waveform deformation phenomenon, an experiment is devised and the results output by the Rogowski coil transformer and low power current transformer are compared and analysed. Several measures to improve the output waveform deformation are proposed, such as increasing the sampling rate of the converter, decreasing the cut-off frequency of the filter, or replacing the digital integrator with the analogue integrator. The researches provide important guidelines for the application of the Rogowski coil current transformer with the digital integrator in the case of frequency aliasing.

Simplified Approach to Evaluate the Combined Uncertainty in Measurement Instruments for Power Systems

This paper presents the study of the propagation of the effects of uncertainties in a typical measurement system for modern power networks. Nowadays there is a strong demand from the electricity industry of simple and ready-to-use solutions for calculating uncertainty in such “new” measurement systems. To this purpose a simplified approach is presented whose results are shown to be in good agreement with those provided by conventional but more complex methods. Two applications, rather simple but very common, are considered in this paper. In the first one, the measurement of a voltage phasor is considered and the measurement chain is made by an low power instrument transformer (LPIT) and a converter used for adapting the level of signals from the LPIT to the inputs of intelligent electronic device. The second application deals with the measurement of active power of a system made by a low power voltage transformer (LPVT), a low power current transformer and a powermeter.

Experimental Investigation Into the Mechanism of 220-kV Vertical-Arrayed Double-Bundle Transmission-Line Conglutination

The mechanism of vertical-arrayed double-bundle transmission-line conglutination is studied in this paper through experiments on a laboratory-based physical model with a 230-m span. Based on the equivalence principle, the conglutination problem in real-world transmission lines has been reproduced in high-voltage and heavy-current experiments where the test circuit is compensated by a series capacitor, so that the output current is continuously adjustable by the voltage regulator and power current transformer. This paper presents, in detail, the experiments carried out, and demonstrated the threshold factors associated with the conglutination phenomenon. The investigation revealed that the number one factor contributing to transmission-line conglutination is the electromagnetic force, which, in turn, is affected by the space between the lines; initial sag and ambient temperature also play important roles. The research results with a thorough understanding of the mechanism of transmission-line conglutination can help provide an understanding of the mechanisms and will enable conduction of numerical analysis of the phenomenon.

Design and Analysis of Multi-Winding Power Current Transformer for Power Transmission Lines Inspection Robot

Special current transformer (CT) is designed to induct power from the power transmission lines for an inspection robot. Equivalent circuit is used for calculating and modelling the parameters of the current transformer. Air gap analysis is given aiming at adapting dynamic range of bar current, and calculation of the effect of air gap is provided in detail. Ratio change of current transformer is introduced by which the secondary current could be adaptive to the bus current. Simulation results show that dynamic control of length of air gap and turns of the coils could make the current transformer be adaptive to the variable bus current and be more convenient for inducing power for the power transmission lines inspection robot.

Magnetic field analysis and leakage inductance calculation in current transformers by means of 3-D integral methods

This paper presents 3D integral approach to power current transformer magnetic field and inductance calculations. A minimization of the kernel norm has been carried out for the integral equation governing the field. The software package TRACAL3, based on the integral methods for field and inductance calculations, has been developed and implemented for personal computers. The application of the 3D mathematical models has been made for the leakage field in a current transformer. The results of calculations were compared with measurement data. The comparison yields good agreement.