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Compared with traditional current transformers (CTs), electronic current transformers (ECT) have the following advantages: (1) no saturation problem, (2) wider measurement range, (3) smaller footpr...

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.

This paper presents a head-dependent model for pump storage units (PSUs) in a power system for short-term generation scheduling over one week. A hydraulic system with upper and lower reservoirs, each having their own in and out river flows, is considered. Hydraulic conditions, as well as head effects, are explicitly modeled for both generation and pumping modes of the PSUs. The problem is solved by the branch-and-cut method to obtain a near-optimal solution. Test results of an hourly generation schedule, including comparisons of pump efficiencies, hydraulic conditions, and operating costs of the PSUs for a real power system, are presented.

Though steady-state power features such as real power ( $P$ ), reactive power ( $Q$ ), and total voltage/current harmonic distortions ( $V_{\text{THD}}/I_{\text{THD}}$ ) may contain sufficient information, adopting them directly for nonintrusive aging load monitoring (NIALM) identification process requires higher computational burden and larger memory. To effectively reduce the number of needed steady-state power features without degrading the performance of NIALM, a Hellinger distance (HD) algorithm is proposed and presented in this paper. To minimize the training time and improve recognition accuracy, a particle swarm optimization (PSO) is adopted in this paper to optimize parameters of training algorithm in artificial neural networks (ANNs). The proposed methods are used to analyze and identify the load characteristics of aging loads in residential buildings. The results show that the accuracy can be improved by using the proposed method.

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.

Traditional current transformers (CTs) suffer from DC and AC saturation and remanent magnetization in many industrial applications. Moreover, the drawbacks of traditional CTs, such as closed iron cores, bulky volume, and heavy weight, further limit the development of an intelligent power protection system. In order to compensate for these drawbacks, we proposed a novel current measurement method by using Hall sensors, which is called the Hall-effect current transformer (HCT). The existing commercial Hall sensors are electronic components, so the reliability of the HCT is normally worse than that of the traditional CT. Therefore, our study proposes a redundancy mechanism for the HCT to strengthen its reliability. With multiple sensor modules, the method has the ability to improve the accuracy of the HCT as well. Additionally, the proposed redundancy mechanism monitoring system provides a condition-based maintenance for the HCT. We verify our method with both simulations and an experimental test. The results demonstrate that the proposed HCT with a redundancy mechanism can almost achieve Class 0.2 for measuring CTs according to IEC Standard 60044-8.

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.

Compared with the traditional load monitoring system, a nonintrusive load monitoring (NILM) system is simple to install and does not need an individual sensor for each load. Accordingly, the NILM system can be applied for wide load monitoring and become a powerful energy management and measurement system. Although several NILM algorithms have been developed during the last two decades, recognition accuracy and computational efficiency remain as challenges. To minimize training time and improve recognition accuracy, particle swarm optimization is adopted in this paper to optimize parameters of training algorithms in artificial neural networks. The proposed algorithm is verified through the combination of Electromagnetic Transients Program simulations and field measurements. The results indicate that the proposed method significantly improves recognition accuracy and computational efficiency under multiple operation conditions.

Current transformers (CTs) are an indispensable equipment for power system current measurement. If a fault occurs in a power system, iron cores of CTs may face saturation problem and cause current measurement errors, resulting in false responses in protection relays. This research proposed a new current measurement technology using Hall integrated circuits (Hall ICs) symmetrically surrounding a power cable to measure the current flowing in it. This new electronic current transformer is called coreless Hall-effect current transformer (HCT). However, there is a dc offset voltage of about 2.5V existing in Hall ICs and thermal drift phenomenon of this dc offset may arise due to ambient temperature. Both are factors affecting accuracy of the HCT. This paper proposes an automatic dc offset calibration method to eliminate the dc offset voltages of Hall ICs and also uses digital filters to filter out noises to get better accuracy. This research also follows IEC 60044-8 electronic current transformer standard to perform the current accuracy test. Results show that accuracy can achieve class 0.5 for measuring CTs.

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...

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.

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.

A power-failure event occurred at the third nuclear power plant (TNPP) in Taiwan in 2001. A chain of events began at 09:36 p.m. on March 16 due to insulation failure associated with flashovers on the 345-kV transmission line. As a result, the 4.16-kV engineered safety features (ESF) buses at the TNPP experienced a loss of power for 2 h and 8 min. This accident was a class 3 emergency (e.g., a class 4 emergency will lead to an overall evacuation of local residents) based on the declared class of emergency in Taiwan. The purpose of this paper is to describe and analyze the chain of events leading to the loss of electrical power. Conclusions on the causes of the outage are drawn and modifications of the system structure are made to improve safety and reliability in a nuclear power plant.

Although steady-state power features such as real power (P), reactive power (Q), and total voltage/current harmonic distortions (VTHD/ITHD) may contain sufficient information, adopting them directly for non-intrusive aging load monitoring (NIALM) identification process requires longer computation time and larger memory. To effectively reduce the number of steady-state power features representing load aging signals without degrading performance, a Hellinger distance (HD) algorithm for extracting the power features of NIALM is proposed and presented in this paper. To minimize the training time and improve recognition accuracy, a Particle Swarm Optimization (PSO) is adopted in this paper to optimize parameters of training algorithm in Artificial Neural Networks (ANNs). The proposed methods are used to analyze and identify the load characteristics of aging loads in residential buildings. The recognition result shows that the accuracy can be improved by using the proposed method.

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.

Summary form only as given. A Le-Blanc transformer is a special winding connection transformer for the single-phase power supply of electrified railway and it has been installed in the electrified railway of Taiwan (Tairail) for more than twenty years. It is well-known that the main electrical protection of large capacity transformers is differential protection. As the special winding connection and current relationship of Le-Blanc, differential relays are not easy to apply directly without using the special turn ratio current transformers. Therefore, the purpose of this paper is to design a differential protective scheme that is built by normal turn ratio current transformers connected for Le-Blanc transformers. According to the phasor combination method, a two-relay differential protective scheme that combines the primary line currents to match the secondary line current phases of Le-Blanc is proposed in this paper. For evaluating the performance of the proposed scheme, a practical design example using the parameters of a Tairail's Le-Blanc transformer and some scaled down data of the field test system in their laboratory are also presented in this paper.

A detailed model of the R-L-fed inverting substation, for use of power flow and harmonic studies in DC electrified transit systems, has been presented in this paper. A unified Newton-Raphson method is adopted as the solution approach of the AC/DC power flows. The harmonic study is performed by the Y-bus method using the derived harmonic current injections of the converter. The Chungho Line of Taipei Rapid Transit Systems is given as a numerical example system. Effects of the application of inverting substations to the example system are investigated. The detailed converter model and the fast power flow algorithm can be easily applied to train simulators to complete a more accurate and rapid electric network solution of transit systems.

In general, conventional Optimal Power Flow(OPF) solutions utilize some optimization techniques at a single case. In the OPF solution method, all the available variables are used to solve the problem. In practical operation, such a solution is not a practical consideration because the control actions would be too many to be implemented. In this paper, sensitivity factors combined with dynamic programming technique are used to solve short term (one day) dynamic optimal power flow. A two-step real time real power dispatch method considering inconforming load change is used to solve real power dispatch, and then, the sensitivity factors are used to solve reactive power dispatch with some constraints. Finally, the dynamic programming technique is used to minimize the control actions to as little as possible. The advantages of this method are simple and easy to implement, and it would greatly enhance the operators' planning.

Parallel operation of two 6-n prepulse uncontrolled bridge rectifiers, to obtain a 12-pulse rectification, without an interphase transformer connected on the DC sides is investigated in this paper. The mechanism of interactions between the two six-pulse bridges is analyzed. As the load current varies from no-load to the complete short-circuit value, seven modes of operation are recognized. Equations describing the mean output voltage and various operating angles of the rectifier circuit are given in terms of a reactance factor. Voltage regulation and variations of the ignition angle and the commutation overlap angle for rectifiers with and without an interphase transformer are also compared.

The main electrical protection of Le-Blanc connection transformers that supply the single-phase power to the electric railway in Taiwan is the overcurrent protection. This paper presents a more complete protective scheme, the differential protection, for Le-Blanc by phasor combination method. The calculation procedure and the good mismatch results of a practical design example using the parameters of a Le-Blanc transformer of Taiwan Railway Bureau (Tairail) are described in this paper. In addition, using the normal current transformers and electromagnetic type transformer differential relays to completely construct the protective scheme is another merit of this algorithm.

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%.

The paper applies the advanced multi‐pass dynamic programming (AMPDP) to solve the weekly hydrothermal generation coordination problem with direct load control (DLC) operation. The AMPDP technique can overcome the long calculation time and large data storage problems that the conventional dynamic programming (DP) method fails to resolve for large power systems and long scheduling period. The algorithm developed in this paper finds the optimal hydrothermal coordinated generation schedule of a power system that includes 48 thermal units and 8 hydro units with direct load control during a 192 hour study period. For the energy payback phenomenon of direct load control of air conditioner, the simulation of various energy payback patterns and various controllable capacities are presented in this paper.

The paper presents a new formulation of harmonic current injection of the 6‐pulse uncontrolled bridge rectifier with commutation impedance. In cooperation with a train simulator developed earlier, the proposed harmonic source model is applied in a harmonic analysis program to comprehensively simulate the harmonic penetration in the Blue Line of Taipei Rapid Transit Systems (TRTS). Both frequency scans and harmonic distortion calculations were performed for various system component models. Simulation results indicated that both the voltage and current harmonic distortions in the Blue Line of TRTS were improved by use of 24‐pulse rectifiers. The application of further harmonic suppression schemes in traction networks to alleviate the harmonic distortions can be achieved using the simulated results.

This paper applies the sensitivity factor method to the reactive power/voltage dispatch problem and combines it with the fast Newton-Raphson economic dispatch to solve the optimal power flow problem. The advantage of this method is that it is fast and reliable. Firstly, the real power generalized generation shift distribution (GGSD) factors are used in economic dispatch to find the real power generation for every unit so that the fuel cost is minimum. During the process of solving the economic dispatch problem, the voltage magnitudes of load buses in a power system may be changed and may exceed the ranges of secure values. Therefore, reactive power sensitivity factors of bus voltage magnitudes are used to regulate the voltage magnitudes of load buses to the secure ranges. The process is repeated to find the optimal generation with all voltages staying within the secure ranges. Results show that the algorithm converges very fast. >

There are many algorithms reported in the literature to forecast the total real load of a power system. But in a power system, the local area loads (both real and reactive loads) are more helpful for dispatching center operators to schedule generation outputs. An approach to substation load (both real and reactive power) forecast by an artificial neural network (ANN) is presented in this paper Characteristic data of substation load collected continuously by the Supervisory Control and Data Acquisition (SCADA) system of the dispatch center are used for the forecast. The characteristic data include substation historical loads, ambient temperature, relative humidity, system frequency, substation voltages, shunt capacitor status and transformer tap ratios. Since the forecast is based on data acquired by SCADA, the time interval between data samples can be as short as minutes or even seconds; thus, the forecasted load model is suitable for dynamic load studies. Furthermore, the algorithm to vary the n...

Because of lower voltage levels and smaller power ratings, the R/X ratio of commutation impedance in industrial AC/DC distribution systems is usually higher than that in HVDC transmission systems. Considerable discrepancies may therefore occur in industrial AC/DC power flow results, especially the reactive power consumption of converters, if the commutation resistances of the converters are neglected. To describe the effects of commutation impedance on converter operations and to precisely relate the fundamental line current and DC output current of the converter, a detailed model of the bridge converter with commutation impedance for use of Newton-Raphson power flow studies in industrial AC/DC power systems is derived in this paper. A coal mine power system and a DC electrified transit railway system with regenerative braking function, a part of Taipei Rapid Transit Systems under planning, have been analyzed to show the improved accuracy and good convergence characteristics of the developed Newton-Raphson power flow formulation with the proposed converter model. >

The dispatch of air conditioner direct load control (DLC) using multi-pass dynamic programming (MPDP) methods is presented. The objective of this work is to schedule the control of air conditioner load by MPDP methods such that the peak load reduction and production cost saving have optimum results for the whole study period. The algorithm can quickly converge to an optimal schedule. To demonstrate the effectiveness of this approach, results of a sample study on the Taiwan Power Company power system are described in this paper. >

This paper sets up a formulation to determine the optimal contract capacities and optimal sizes of battery energy storage systems for time-of-use rate customers. The advanced multi-pass dynamic programming and expert knowledge base rules are then applied to solve this problem. Two industrial customers of the Taiwan Power Company System are used as examples to test this algorithm. Results show that the optimal sizes of battery energy storage systems and the optimal contract capacities of customers during the life cycle of battery energy storage systems can be achieved by this algorithm; therefore the maximum economic benefits of battery energy storage systems for time-of-use rate customers can be estimated. >

Comparing with the traditional load monitoring system, Non-Intrusive Load Monitoring (NILM) system is simple to install and does not need individual sensor for each load. Accordingly, the NILM system can be applied for wide load monitoring and become a powerful energy management and measurement system. Though several NILM algorithms have been developed during the last two decades, the recognition accuracy and computational efficiency remain challenges. To minimize the training time and improve recognition accuracy in Artificial Neural Networks (ANNs), a Particle Swarm Optimization (PSO) is adopted in this paper to optimize parameters of training algorithm in ANN to improve NILM accuracy. Case studies are verified through the combination of Electromagnetic Transients Program (EMTP) simulations and field measurements. The results indicate that the proposed method significantly improves the recognition accuracy and computational speed under multiple operation conditions.

In recent years, image recognition, along with improvements in image processing technology, has become a mainstream method of object inspection. The quality of images directly affects the image-recognition rate. Track monitoring systems play an important role in ensuring safety and preventing derailments of trains, on the basis of the prevailing track conditions. Therefore, the conditions of track systems are very important. In this research, a high-speed frame grabber system is designed. The triggering rate of its line scan camera can be adjusted to match the vehicle speed of the train, so that the pixels per inch of images captured by this camera are fixed. The hardware equipment of the designed system includes a line scan camera, an image acquisition card, artificial lightings, a contrast sensor, and a system on a programmable chip (SOPC) development board. An exposure time control system is designed on the basis of a field-programmable gate array (FPGA) core. The designed system can acquire clear high-speed images while the vehicle speed changes dramatically. The experimental results confirm the feasibility of using line scan cameras for railway vehicles.Copyright © 2011 by ASME

This paper develops a set of reactive power flow distribution factors, a set of voltage sensitivity factors and a set of generator reactive power participation factors for reactive power outage studies. Using these factors, the transmission branch flows, bus voltage magnitudes and adjusted outputs of reactive power sources in the post‐outage state can quickly and accurately be calculated. Also, those generators, synchronous condensers, shunt capacitors and reactive power load outages which cause violations of specific criteria can rapidly be identified. The derivation of these factors is based on the decoupled load flow characteristics and network sensitivity. For system operations, these factors can be used for security assessment either off‐line, as in the planning application, or on‐line as part of an automatic security monitoring scheme.

This paper applies a very efficient new technique, multi‐pass dynamic programming (MPDP) combined with successive approximations, to solve the weekly thermal unit commitment and hydrothermal generation scheduling problem. Conceptually, dynamic programming is suited for solving this problem, but the long computing time and the large storage memory required become unacceptable for large power systems and long scheduling periods. The MPDP technique can overcome these difficulties. Furthermore, the unit start‐up cost and pumped storage plants are considered in the hydrothermal coordination instead of only the production cost as in the previous application. The algorithm is tested on Taipower system with forty thermal units, seven conventional hydro units and one pumped storage plant. The results show that this method is suitable for practical systems.