Korea Electrotechnology Research Institute Research Articles

Vibration analysis of a permanent magnet synchronous motor by a pole/slot combination

A sixteen-pole eighteen-slot (16p/18s) permanent magnet synchronous motor (PMSM) developed in Korea Electrotechnology Research Institute (KERI) for a vertical articulated robot is chosen as a reference model, and other two pole/slot combinations (20p/18s, 20p/24s) are together compared in terms of electrical and mechanical performance. Radial force density varying in time and space is decomposed through Fast Fourier Transform (FFT), and vibration is calculated from the harmonics of radial force. The vibration of 20p/24s is best due to its mode of 4 among the three pole/slot combinations. Additionally, the variation of radial force density with respect to torque is compared between 16p/18s and 20p/18s. Despite the same number of slots in both motors, the slope of 20p/18s is greater than that of 16p/18s in radial force density due to the different number of poles. As a result, the vibration of 20p/18s is worse than that of 16p/18s.

Qualification of Fe0.95Co0.05Si2 as a reference material for high temperature measurement of the thermoelectric power factor

Precise characterization of thermoelectric (TE) materials is mandatory for a meaningful validation of scientific results, focusing on traceable determination of the Seebeck coefficient (S), the electric (σ) and thermal (κ) conductivity. These properties form the thermoelectric figure of merit zT = (S2σ/κ)T, which is used for assessment of TE conversion efficiency with respect to the absolute temperature T. The level of metrological standardization is characterized to date by available reference samples for the Seebeck coefficient, publications on best practice measurement approaches, and accomplished international round robin (RR) campaigns on transport property measurements.We report on the qualification of β-Fe0.95Co0.05Si2 (FeSi2) as the first semiconducting high temperature reference material for the TE power factor (PF = S2σ), which is currently developed by the German Aerospace Center (DLR) and the Physikalisch-Technische Bundesanstalt (PTB). The relation between the size of FeSi2 compacts obtained by current-assisted short time sintering and the resulting functional homogeneity of the material is presented, which is studied by spatially resolved Seebeck coefficient measurements at room temperature. Data from temperature dependent characterization of the PF is provided to assess functional stability and homogeneity under integral measurement conditions. The outcome of certification measurements at PTB report on individual uncertainty contributions as the base for a later testimony of FeSi2 as a metrological reference for the PF. Integral measurements have been expanded to further comparative test results obtained by the Korea Electrotechnology Research Institute (KERI), the Indian Institute of Technology Bombay (IITB), and the Netzsch Gerätebau GmbH. The findings give evidence of an excellent homogeneity, reproducibility and stability with low standard deviations for S and σ far below typical measurement uncertainties, which effectively demonstrates the suitability of FeSi2 as a future reference material for TE metrology at elevated temperatures up to 1000 K.

First Russian 220 kV Superconducting Fault Current Limiter (SFCL) For Application in City Grid

The superconducting fault current limiter (SFCL) for a nominal voltage of 220 kV and a rated current of 1200 A was developed by SuperOx company to be applied in high voltage substation in Moscow, Russia. The device is a three-phase dead-tank apparatus and is equipped with a closed-cycle cryocooling system. Liquid nitrogen serves simultaneously as a cooling and an insulating media. The device makes use of about 25 km of 12 mm wide high-performance 2G HTS wire with uniform properties along the length. High-voltage tests of the device were performed at Korea Electrotechnology Research Institute (KERI) in accordance with the IEEE C37.302-2015 test guide and Russian national standards for high voltage electrical equipment. The installation of the SFCL at substation in parallel with the existing air core reactors was completed in 2019. Since then, the device is in a daily operation. Over this period, SFCL has fully confirmed its design specifications including transmitting over 80 million kWh to customers and experiencing three fault current events.

Examination on the Effectiveness of an Image Processing Technology for the Visibility Enhancement of Firefighters in Fire

In the case of fire, it is important to enhance the visibility of firefighters for emergency activities (for example, fire extinguishment, rescue, and first-aid). In the present study, an image processing technology for visibility enhancement developed by the Korea Electrotechnology Research Institute was used to improve the visibility of firefighters. Image processing technology for visibility enhancement is a technology that combines Multi-Scale Retinex and smoke concentration equalization processing. To examine the effectiveness of the image processing technology in thick smoke conditions, the visibility was classified depending on the smoke generation in an enclosed compartment. In addition, comparative before and after evaluation of image processing technology was performed quantitatively. The visibility was divided into seven levels depending on the recognizable distance of each number plate. Thus, the visibility was improved from a maximum of four levels. Additionally, an in-depth interview was conducted with field crews who are the consumers of this technology; a view of more than 3.5 m was required to use this technology in fire fields.

Electrical and Mechanical Characteristics of a High-Speed Motor for Electric Turbochargers in Relation to Eccentricity

As the demand for eco-friendly, high-efficiency transportation technologies increase due to climate change, a high-speed electric motor, a key component of an electric turbocharger, has been developed that can reduce emissions and increase fuel efficiency. Korea Electrotechnology Research Institute with Keyyang Precision Co., Ltd., developed a high-speed surface-mounted permanent magnet synchronous motor. It operates at a power of 3 kW at 100,000 rpm and is intended to fit 1600 cc diesel vehicles. In this paper, the electrical and mechanical characteristics of the high-speed motor were reviewed in consideration of the effect of eccentricity among the various causes that affect vibration. It was confirmed that eccentricity affected the distribution of the electromagnetic force and inductance of the winding due to the uneven air-gap. Additional vibration was generated at the half of pole passing frequency (1666.67 Hz). Diagnosing the presence or absence of eccentricity when driving a motor takes a great deal of time and cost because the load is separated or the motor is diagnosed through disassembly and measurement. The characteristics of eccentricity identified in this paper can be checked using a relatively simple method when diagnosing the presence or absence of actual eccentricity.

Evaluation of Electromechanical Properties in Multiple HTS Layered Conductors at 77 K

High engineering critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ) is demanded in high-performance large-scale applications such as power cables, high-magnetic-field magnets, accelerators, and fusion reactors. In developing high current capacity and low vulnerability under a high magnetic field, high-temperature superconducting (HTS) rare-earth barium copper oxide coated conductors (CCs) have undergone various trials, and CC tape characteristics have ultimately been greatly improved. The Korea Electrotechnology Research Institute recently developed a “multiple HTS layers on one substrate” (MHOS) conductor that can carry high critical current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , based on the number of superconducting layers deposited on one substrate. The superconducting layers in a MHOS conductor are much thicker than in a single-layered CC tape, possibly affecting the degradation behaviors of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> under a mechanical load. To ensure the performance and reliability of MHOS conductors, it is necessary to evaluate the strain/stress response of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . In this study, the electromechanical properties of MHOS conductors were investigated using the uniaxial tension test method as well as the single-sided bending test at 77 K and self-field and at 0.5 T using a pair of neodymium permanent magnets.

Design of a Novel Inductive Type Fault Current Limiting HTS Power Cable

In a power system, fault currents are on the rise and are becoming a common problem. Moreover, several methods for the restriction of fault currents can lead to the instability of power system. In the Republic of Korea, the Korea Electrotechnology Research Institute is carrying out the development of a 154 kV class high temperature superconductor (HTS) cable with a fault current limiting function since May 2017. In this project, a novel inductive type fault current limiting (IFCL) HTS power cable is proposed. This paper presents the design of an IFCL-HTS cable for a transmission system, whose principle is based on change in the distribution of magnetic fields around the cable using a quench of HTS shield layer. The results of the design and simulation for performance prediction are discussed in detail.

Investigation of Human and Model Observer Performance of Mass Detection in a Prototype Digital Breast Tomosynthesis System

Task-based assessment of image quality using a theoretical observer model has recently gained attention in medical imaging fields. Observer models whose performance can suitably match that of a human observer under various imaging conditions have been considered a key concept for virtual clinical studies. This work focused on experimental study in which a prototype digital breast tomosynthesis (DBT) system, developed by the Korea Electrotechnology Research Institute, was used to compare the task-based Fourier metrics of a detectability index with the performance of human observers. Different angular ranges of ±7°, ±10.5°, ±14°, ±17.5°, ±21°, and ±24.5° were used to detect four different sizes of spheroidal masses with the same 15-projection samplings. A total of 16 human observers participated in the study. Human observer performance was measured using four-alternative forced choice (4AFC) tests for different detection tasks, including detecting spheroidal masses. To determine the task-based detectability index (d′), the non-prewhitening matched filter observer was calculated by analyzing the task function, local spatial resolution, and local noise of spheroidal masses. The percentage of signals correctly detected (Pc) with the 4AFC tests was then compared with the detectability index for tasks presented in 2D slices (dslice′2). The average Pc for 16 human observers was 0.87 (range = 0.56–1). Results showed that Pc decreased as the angular range increased from ±7° to ±24.5° with different mass sizes. Our result also showed that the performance of the task-based theoretical model observer could reasonably estimate d′ for all inserted lesions of different sizes and acquired under different conditions, while presenting a trend similar to those of the human observers. Consequently, our study is expected to contribute to quantitative imaging performance analysis under various DBT imaging acquisition parameters.

Impact of Smart HTS Transmission Cable to Protection Systems of the Power Grid in South Korea

In South Korea, Korea Electrotechnology Research Institute (KERI) has developed a 154 kV smart High Temperature Superconducting (HTS) cable system with fault current limiting function since May 2017. This project is funded by the Ministry of Trade, Industry, and Energy of Republic of Korea. It is very important to design the protective relay system for a successful application of the smart HTS cable system to a practical power grid. In general, the smart HTS cable can have a negative impact on the protective coordination in power transmission system because of the variable impedance of the cable. This paper reviews some protection problems which can be caused by the application of the 154 kV smart HTS cable to power transmission systems in Korea and proposes a protection scheme for a test power system. And then we conduct a basic study to find solutions for the problems using an electromagnetic transient program, PSCAD/EMTDC.

Development and HIL Testing of a Protection System for the Application of 154-kV SFCL in South Korea

In South Korea, a 154-kV single-phase superconducting fault current limiter (SFCL) system was developed and installed at the Gochang power test center of Korea Electric Power Corporation in 2016. Korea Electrotechnology Research Institute proposed a novel protection algorithm for the application of 154-kV SFCLs to a real power system and designed a protection scheme of the Gochang power test center. This paper verified the protection scheme using the hardware in the loop testing that a commercial protective relay system with the novel algorithm is tested by real time digital simulator.

The novel short circuit withstand test configuration for ITER VS1 power transformer

The ITER (International Thermonuclear Experimental Reactor) Coil power supplies will be installed to provide controlled DC power to the superconducting tokamak magnets for plasma operation. The short circuit withstand test is required to the ITER power supply for safety. Among several ITER coil power supplies, VS1 power supply is to dedicate plasma vertical stabilization (VS). In accordance with IEC standards, the single phase input voltage which is different from the three phase input voltage could be used for the short circuit withstand. To satisfy the electromagnetic force deviation of IEC standard, we propose a novel short circuit withstand test method using the single phase voltage. The short circuit withstand test of VS1 power transformer is successfully performed by the proposed method in the KERI (Korea Electrotechnology Research Institute).

Multiphysics analysis of a high speed PMSM for electric turbo charger

The ETC (Electric Turbo Charger) consists of high speed PMSM, ball or air foil bearings, impeller and controller. KERI (Korea Electrotechnology Research Institute) is developing a high speed surface permanent magnet (SPM) type of synchronous motor and a Pulsed Width Modulation (PWM)-driven inverter . This system operates at a power density of 3 kW/kg at 100,000 rpm and is intended to fit the 1,600 cc diesel vehicles to reduce turbo-lag within 0.5 s. The design and analysis of the PMSM for the ETC has been developed successfully considering the several losses and current overload rates using transient computational fluid dynamics (CFD).

Design and Experimental Validation of a High-Speed Electric Turbocharger Motor Considering Variation of the &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${\boldsymbol{L}}/{\boldsymbol{D}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Ratio

The commercialized electric turbocharger (ETC) made by Valeo includes a high-speed switched reluctance motor (SRM), ball bearings, impeller, and controller. SRMs are generally very noisy and have low efficiency (70%) at high speed. No ETC has yet been commercialized that includes a permanent magnet (PM) motor. The Korea Electrotechnology Research Institute, Changwon, South Korea, is developing a high-speed surface PM type of synchronous motor and a pulse width modulation-driven inverter. This system operates at a power density of 3 kW/kg at 100000 r/min and is intended to fit 1600 cc diesel vehicles to reduce turbolag to within 0.5 s. The design and analysis of the PM synchronous motor (PMSM) for the ETC have been successful by considering the electric and mechanical performance using multiphysics analysis. Validation by experiment was performed and matched within 1% error in terms of the efficiency. Design, analysis, and experiments with the PMSM for ETC applications were conducted successfully by utilizing an action–reaction torque sensor and the resistance load test method.

Effective detective quantum efficiency of two detectors in a prototype digital breast tomosynthesis

Digital breast tomosynthesis (DBT) system is a novel imaging modality that strongly depends on the detector performance. The effective detective quantum efficiency (eDQE) is a newly accepted system of performance analysis metric that solves the disadvantages of conventional DQE evaluations, which do not consider clinical operating conditions. To evaluate the eDQE, we used the direct-conversion based Anrad detector and the indirect-conversion based Dexela detector. Our aim is to study the performance of such detectors when they are mounted on a prototype DBT system. The prototype DBT system consists of a CsI(Tl) scintillator/CMOS-based flat panel digital detector and an a-Se based direct conversion detector developed by the Korea Electrotechnology Research Institute (KERI). The performance of the two detectors was compared on the basis of scatter fraction, transmission factor, effective modulation transfer function (eMTF), and effective normalized noise power spectrum (eNNPS). As a result, the Dexela detector is characterized by a decreasing eNNPS trend as the spatial frequency increases, whereas the Anrad eNNPS looks almost independent of the spatial frequency. The eMTF was found to be higher in the Anrad detector compared to that in the Dexela one for all frequencies. The eDQE values at 1 cycle/mm (low frequency) were 0.11 and 0.17 for the Anrad and Dexela detectors, respectively, and the values of the spatial frequency feDQE(0.1), corresponding to eDQE = 0.1, were 1.25 and 2.81 cycles/mm for the Anrad and Dexela detectors, respectively. The Dexela detector also presented a higher contrast-to-noise ratios (CNRs) for all different sizes of μCa groups, thus demonstrating overall better eDQE results in imaging performance compared to the Anrad detector.

Protection Scheme of a 154-kV SFCL Test Transmission Line at the KEPCO Power Testing Center

This paper presents the design of a protection scheme of a short 154-kV test line with a 154-kV superconducting fault current limiter (SFCL) in the Gochang Power Test Center of Korea Electric Power Corporation. The scheme includes a new protection algorithm proposed by Korea Electrotechnology Research Institute for protecting the SFCL system. The protection scheme is verified by protective coordination simulations on a Gochang power system using PSCAD/EMTDC program in this paper.

Effects of the pole-slot combination on the PMSM of an integrated motor propulsor for an unmanned underwater vehicle considering its electric performance, noise and vibration

The integrated motor propulsor (IMP) is a new unmanned underwater vehicle (UUV) propulsion apparatus. The IMP consists of a rim-driven motor, a fluid hydrodynamic bearing, and a propulsor. KERI (Korea Electrotechnology Research Institute) is developing a surface permanent magnet (SPM) type of synch ronous motor and a PWM-driven inverter. This system operates at a power density of 50HP (37 kW) at 1,000 rpm and is intended to fit the IMP system. The optimum design of the PMSM for the IMP has been developed successfully considering the pole-slot combination, electric performance, and the noise and vibration characteristics using multi-physics analyses and statistical design of experiments (DOE). A back-to-back performance test rig was proposed and considered for operation in a water tank. The acoustic field in a water tank of an optimum model was compared with that in an air condition considering the FSI (fluid structure interaction) dynamics.

Characterizing X-ray detectors for prototype digital breast tomosynthesis systems

The digital breast tomosynthesis (DBT) system is a newly developed 3-D imaging technique that overcomes the tissue superposition problems of conventional mammography. Therefore, it produces fewer false positives. In DBT system, several parameters are involved in image acquisition, including geometric components. A series of projections should be acquired at low exposure. This makes the system strongly dependent on the detector's characteristic performance. This study compares two types of x-ray detectors developed by the Korea Electrotechnology Research Institute (KERI). The first prototype DBT system has a CsI (Tl) scintillator/CMOS based flat panel digital detector (2923 MAM, Dexela Ltd.), with a pixel size of 0.0748 mm. The second uses a-Se based direct conversion full field detector (AXS 2430, analogic) with a pixel size of 0.085 mm. The geometry of both systems is same, with a focal spot 665.8 mm from the detector, and a center of rotation 33 mm above the detector surface. The systems were compared with regard to modulation transfer function (MTF), normalized noise power spectrum (NNPS), detective quantum efficiency (DQE) and a new metric, the relative object detectability (ROD). The ROD quantifies the relative performance of each detector at detecting specified objects. The system response function demonstrated excellent linearity (R2>0.99). The CMOS-based detector had a high sensitivity, while the Anrad detector had a large dynamic range. The higher MTF and noise power spectrum (NPS) values were measured using an Anrad detector. The maximum DQE value of the Dexela detector was higher than that of the Anrad detector with a low exposure level, considering one projection exposure for tomosynthesis. Overall, the Dexela detector performed better than did the Anrad detector with regard to the simulated Al wires, spheres, test objects of ROD with low exposure level. In this study, we compared the newly developed prototype DBT system with two different types of x-ray detectors for commercial DBT systems. Our findings suggest that the Dexela detector can be applied to the DBT system with regard to its high imaging performance.

부분방전검출 신뢰도 향상을 위한 UHF 센서개선 및 성능검증

GIS(Gas Insulated Switchgear) is important power apparatus which have strong dielectric strength, supply electric power and is a part of the power system. Most substation type is configured as GIS. Recently, because of continuous increasement of GIS demand resulted from high quality & big capacity of electric power, the necessity of the preventive & diagnosis system is being expanded gradually. GIS partial discharge occurred on the UHF band is detected effectively by the method to IEC 60270 that recommend to be able to detect the apparent minimum discharge, 5 pC. Additionally, the UHF sensor should be installed to detect PD signal if Partial discharge signal, 5 pC occur in every part of GIS. Currently PD diagnosis system applying UHF sensor for GIS with various voltage level like 154 kV, 345 kV, 765 kV have been operated. And it is necessary to measure and analyze insulation breakdown phenomenon of inside GIS exactly. In this paper, we proposed Fat-dipole patch UHF sensor that is developed and more sensitive, excellent wide-range characteristic than the exising UHF sensor. And we performed KERI (Korea Electrotechnology Research Institute) reference test, which showed the excellent result for the all tests.

Erratum for: Food inspection system using terahertz imaging

In the above-mentioned article, which appeared in Microwave and Optical Technology Letters, Volume 56#5, DOI 28303, the authors neglected to add the Acknowledgement listed below: This work was supported by the Joint Research Project of the Korea Research Council for Industrial Science and Technology (ISTK), South Korea. Also, this research was supported by Korea Food Research Institute (KFRI), Korea Electrotechnology Research Institute (KERI) and Modern Hightech Co. LTD., South Korea. The authors regret any confusion that resulted from the omission of this information.

Progress in research and development for REBCO coated conductors by reactive co-evaporation

This paper reviews recent progress in research and development (R&D) of reactive co-evaporation for high performance REBCO coated conductors in Korea. Two types of reactive co-evaporation methods were developed for the deposition of SmBCO and GdBCO superconducting layers respectively on the IBAD (Ion Beam Assisted Deposition)-MgO template in the Korean coated conductor project. Batch type reactive co-evaporation equipment and its processing were developed for SmBCO coated conductors at Korea Electrotechnology Research Institute (KERI) in conjunction with the Korea Advanced Institute of Science and Technology (KAIST), and a very high critical current exceeding 1,000 A/cm at 77 K in the self field was achieved through the optimization of deposition parameters. Reel-to-reel type reactive co-evaporation processing with a high conversion rate was also developed, while long length GdBCO coated conductors have been routinely produced by SuNAM Co. The minimum critical current of 422 A/cm-w at 77 K in self field was confirmed for 1 km-long GdBCO tape.