Kun-Long Chen

A New Method for Power Current Measurement Using a Coreless Hall Effect Current Transformer

A new method for performing power current measurement is proposed; this method involves the use of Hall sensors without iron cores. A new apparatus for implementing this method, called coreless Hall-effect current transformer (HCT), has been developed. The HCT consists of four Hall sensors connected to a weighted adder. Four Hall sensors are symmetrically attached to an electric conducting cable, and the output of the sensors is connected to the weighted adder. The weighted adder performs the “average” operation, thereby obtaining the average voltage. Since the average Hall voltage is obtained, the HCT can eliminate the ambient interference. A measurement framework is designed and implemented to compare a series of waveforms obtained by HCTs with those measured by traditional current transformers (CTs) and linear CTs. Current measurement results show that an HCT can measure current with greater accuracy than traditional CTs. Moreover, in the presence of faults, HCTs do not encounter problems related to saturation that exist in traditional CTs.

New Electronic Current Transformer With a Self-Contained Power Supply

Summary form only given. Compared with traditional current transformers (CTs), electronic current transformers (ECTs) are characterized by small volume, light weight, good isolation, good linearity, and easy digitization. Hence, ECTs are one of the primary devices for signal digitization for supervising intelligent substations. We design a coreless ECT using Hall sensors as well as its mechanism and circuit configuration in order to replace traditional CTs and other CTs. The proposed ECT achieves accuracy Class 0.5 for measuring CTs and accuracy Class 5P21 for protective CTs according to IEC Standard 60044-8.

Multifunctional Coreless Hall-Effect Current Transformer for the Protection and Measurement of Power Systems

This paper presents a multifunctional coreless current transformer based on the Hall effect (multifunctional HCT), and designs its actual electronic circuit that can discriminate load and fault currents to perform both metering and protective functions. The multifunctional HCT has two primary circuits: 1) distinguishes the load current from the fault current and 2) delivers the current value using an analog multiplexer. This HCT can eliminate the 2.5±0.05 V offset voltage of commercial Hall sensors. It possesses two amplifiers with different gains. Therefore, this multifunctional HCT accurately measures power currents during the operations in measurement systems and protection systems. Using a low-pass filter, the multifunctional HCT is not only capable of reducing noise interference, but also improves the accuracy of power current measurements. The experimental results show that the multifunctional HCT can exhibit an accuracy class of 0.5 for both the measurement and protection of power systems within IEC standard 60044-8. Because the proposed multifunctional HCT does not have core and saturation problems, the accuracy class and limit can achieve the standard accuracy limit factor grade of 63.

Design of a Hall Effect Current Microsensor for Power Networks

Current transformers (CTs) are used to measure line currents in a power network for indicative and protective purposes. However, due to magnetic hysteresis in the cores, traditional CTs may saturate when they detect large fault currents. Thus, a more efficient and accurate device is required. This paper aims at designing a more economical device, a microsensor to measure power network currents. The characteristics of this new design are measured and discussed. The new component will not be saturated for fault currents as high as 40 kA and can be used directly with an intelligent protective system or a digital meter for smart metering of electric power networks if it is designed with an integrated circuit (IC) chip.

Replacing current transformers with power current microsensors based on hall ICs without iron cores

Current transformers (CTs) are adopted in power systems to measure magnitudes of currents for metering and fault protection. Since power system fault currents contain large direct current offsets, they can saturate the iron cores of the current transformers. This saturation phenomenon in iron cores will cause the protective system to make false responses. Furthermore, bulky volume of CTs also imposes restriction on their other applications. Hall integrated circuits (ICs) have high sensitivity and quick response time, and can measure a wide range of magnetic fields. Due to these attributes, this research designs a power current microsensor based on a Hall IC without an iron core. The applying Hall IC measures the magnetic field generated by a power cable and subsequently, the electric current flowing in the electric conducting cable. A measurement framework is designed and implemented to compare a series of waveforms obtained by the Hall IC with those measured by a traditional CT. This study assesses the feasibility of replacing traditional CTs with power current microsensors based on Hall ICs.

Design of a Novel Power Current Micro-Sensor for Traction Power Supply Using Two Hall ICs

This research applied the integrated circuit (IC) manufacturing technology to develop a new power current micro- sensor to replace CTs and save space in railway train sets. Two small pieces of IC chips are attached to a power cable to measure the current flowing in the cable. Measurement results show that the new power current micro-sensor can perform the same function of a CT without running into saturation problems no matter whether the cable is straight or not. Under this method, the two Hall voltages produced by the two Hall ICs will compensate for each other to raise the accuracies of the power current micro-sensors without cores in a non-straight conducting cable. According to the measuring framework developed by this study, based on LabVIEW, a series of waveforms generated by the newly designed power current micro-sensors are compared with those of traditional CTs and linear CTs. Satisfactory results show the feasibility of improving the power current micro-sensor with the new design.

Application of power current microsensors to current measurements in gas-insulated switchgears

Modern primary distribution substations often adopt SF6 gas insulated switchgears (GISs) to reduce the overall construction space. Traditional current transformers (CTs), which are generally used in GISs for current measurement, consist of magnetic cores. These cores are bulky and increase the minimum space required inside GISs. Moreover, the occurrence of faults causes saturation in traditional CTs; this leads to distortion of detected current waveforms, which in turn triggers false responses in protective systems. The recently proposed power current microsensors based on the Hall effect have many advantages over traditional CTs, including smaller volume, quicker response, and wider measurement range, and they do not face the above-mentioned saturation problem. This study assesses the feasibility of replacing traditional CTs inside GISs with power current microsensors, taking into account certain actual conditions, including: (1) the actual distance between two adjoining cables inside GISs, (2) the worst unbalanced three-phase loads allowed by typical primary distribution substations, and (3) the four most common faults occurring in primary distribution substations. Current simulation and measurement results show that power current microsensors can measure current as accurately as traditional CTs. Moreover, during faults, microsensors do not encounter problems related to saturation, which exist with traditional CTs.

New electronic current transformer with a self-contained power supply

Compared with traditional current transformers (CTs), electronic current transformers (ECTs) are characterized by small volume, light weight, good isolation, good linearity, and easy digitization. Hence, ECTs are one of the primary devices for signal digitization for supervising intelligent substations. We design a coreless ECT using Hall sensors as well as its mechanism and circuit configuration in order to replace traditional CTs and other CTs. The proposed ECT achieves Class 0.5 accuracy for measuring CTs and accuracy Class 5P21 for protective CTs according to IEC Standard 60044-8. An additional power supply is required to drive the ECT. Considering that there are no usable power supplies for special measurement environments, we use the surrounding magnetic fields induced by the cable currents as the power supply. A self-contained power supply is proposed and integrated with a backup battery power supply and a battery protection circuit to ensure that power is supplied for different operating conditions. In addition, we design a protective device to protect the back-end circuits of the self-contained power supply in case of a fault occurring in the power system.

Design of a new Hall overcurrent protection relay with instantaneous characteristics

Traditional current transformers (CTs) detect fault currents and transfer signals to overcurrent protection relays for indicative and protective purposes as a part of the protection coordination system in a power network. By characterizing the transient response to a power failure, a reliable and accurate protection relay can be achieved. In this study, we propose a new Hall overcurrent protection relay (HCO) using Hall effect CTs based on the transient exponential signatures of fault current analysis. To minimize the distortion phenomena seen in fault current measurements because of the hysteresis caused by the CTs’ iron cores, and to obtain faster tripping signals, we adapt an HCO to accurately detect nonsinusoidal fault waves and to improve protection coordination accuracy. The experimental results indicate that the HCO significantly improves the protection system’s accuracy and response speed for various power systems applications.

The wireless transmission design of a novel electronic current transformer

This study presents a novel electronic current transformer (ECT), which is based on the Hall current transformer (HCT), and a wireless transmission system. The novel ECT is aimed to be used in both measuring and protective current transformers, and the design of the wireless communication makes ECTs more flexible for current measurements at different current levels in power systems. The novel ECT can be separated into three main circuits, including sensing signal processing circuit, analog-to-digital conversion circuit, and wireless circuit. Firstly, the scale of measured current is classified into small current, middle current, or large current. Then, analog to digital converter digitize the classified signal. Finally, ZigBee device transmits the signal wirelessly to the data acquisition/monitoring system. If electric currents are detected as small or middle current levels, Irms and the reconstructing current proposed by this study will be sent to the monitoring system. Moreover, if electric current is detected as large/fault current level, an alarm will be sent immediately to monitoring system, and 10 cycles of the actual current will be sent later. Besides, LabVIEW is used to build the data acquisition/monitoring system and the measurement result shows that the percentage current error between the transmitted signal from the ECT and the original signal is below 0.15%.