• Polymer(Korea)
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• v.24 no.5
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• pp.621-628
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• 2000

Microporous polypropylene (PP) membranes have the high chemical and corrosion resistance, the good mechanical properties and the thermal stability under high temperatures, but its application is restricted within narrow limits due to hydrophobicity of membranes. In order to impart permanent hydrophilicity to the PP microfiltration membrane, the radiation-induced graft of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc) containing hydrophilic functional group onto the membrane has been studied. The effect of graft conditions such as reaction time, total radiation dose, reaction temperatures, acid compositions on graft yield was investigated. Modified PP membranes were shown to cause an increase in the gas flux. Oil emulsion permeation flux of both original PP membrane and modified PP membrane was examined.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1603-1605
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• 1994

Recently, Gas Circuit Breakers are rapidly replacing Vacuum Circuit Breakers in the medium voltage switchgear. This is due to the improved performance of - GCB in interrupting capability, price, weight, size etc., while the countermeasure to suppress the switching surges of VCB has not been satisfactory. Intensive research works on the GCB have been conducted in the world widely since 1980. Nowadays it is well known that the thermal expansion type GCB can provide- better performance than puffer type in the distribution power system. KERI has conducted researches in the GCB rated at 25.8kV 25kA with Jinkwang Co. using the thermal expantion principle since 1993. In this paper, the calculated results of electric and magnetic fields for the model GCB are presented and analyzed. The effect of permanent magnet used to improve the interruption capabilty at the low current level is also investigated. The design parameters for the interrupter inspected through the short-circuit tests conducted at high power laboratory of KERI.

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.207-216
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• 2015

Amanifold is one of the essential subsea oil and gas production components to simplify the subsea production layout. It collects the production fluid from a couple of wellheads, transfers it to onshore or offshore storage platforms, and even accommodates water and gas injection flowlines. This paper presents the basic design procedure for a manifold frame structure with novel structural verification using in-house unity check codes. Loads and load cases for the design of an SIL 3 class-manifold are established from a survey of relevant industrial codes. The basic design of the manifold frame is developed based on simple load considerations such as the self weights of the manifold frame and pipeline system. In-house software with Eurocode 3 embedded, called INHA-SOLVER, makes it possible to carry out code checks on the yield and buckling unities. This paper finally proves that the new design of the manifold frame structure is effective to resist a permanent and environment load, and the in-house code is also adaptively combined with the commercial finite element code Nastran.

• The KSFM Journal of Fluid Machinery
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• v.17 no.3
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• pp.19-24
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• 2014

Development of long-term mobile energy sources for mobile robots or small-sized unmanned vehicles are actively increasing. The micro gas turbine generator (MTG) is a good candidate for this purpose because it has both of high energy density and high power density, and 500W class MTG is under development. The designed MTG can be divided into 2 main parts. One part consists of motor/ generator and compressor, and the other one consists of combustor, recuperator and turbine. 500W class MTG is designed to operate at ultra-high speed of 400,000 rpm in high turbine temperature over $700^{\circ}C$ to improve the efficiency. Because the magnetism of NdFeB permanent magnet for the motor/generator could be degraded if the temperature is over $150-200^{\circ}C$, MTG needs the thermal insulation to block the heat transfer from combustor/turbine side to motor/generator side. Moreover, the motor/generator is allocated to get the cooling effect from the rapid air flow by the compressor. This study presents the experimental results to verify whether the thermal insulator and air flow are effective enough to keep the motor/generator part in the low temperature less than $100^{\circ}C$. From the motoring test by using the high temperature test rig, it was confirmed that the motor/generator part could maintain the temperature less than $50^{\circ}C$ under the condition of 1.0 bar compressed air.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.177-186
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• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects in underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Journal of the Korean Institute of Gas
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• v.8 no.3 s.24
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• pp.1-7
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• 2004

The polyethylene pipe can use semi-permanent because of the high corrosion resistance with chemical stability. In addition to, there is the merit that is an easy to establish and to maintain. However, as the reason that it is simply degraded when the polyethylene pipe was exposed to the outside, mainly it is used to lay under the ground with low-pressure gas transportation pipe. In this study, the nondestructive evaluation method was used to maintain the integrity of the polyethylene pipe. We simulated the various defects on the polyethylene pipes, and then the AE signal occurred according to the impact test of steel ball was evaluated by the acoustic emission method. From the results, the waveform and dominant frequency could be distinguishing from the defect shapes of polyethylene pipe. Especially, in the case of notch defect, the AE signals occur different by the angle and depth of the notch.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.11-20
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• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects on underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Tribology and Lubricants
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• v.35 no.2
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• pp.123-131
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• 2019

This study characterizes the coastdown performances of two small electric motors supported on high-speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100-30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30-15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than $0.03N{\cdot}m$.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.124-128
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• 2022

NdFeB magnets have been positioned as the core materials in advanced technologies such as MRI (magnetic resonance imaging), FA (factory automation system), robot, motors, and so on based on the highest magnetic properties. To effectively improve the refined microstructure, the plastic deformation has been known as the good alternatives by the recrystallization. However, it has been regarded as being impossible because of the few slip systems in the RE-Fe-B magnets at room temperature. The purpose of this study was to investigate the possibility of control of grain refinement and magnetic anisotropy of NdFeB alloy powder by the severe plastic deformation. The NdFeB magnet powder was fabricated by gas atomization process, and the powder was pre-compacted at high temperature. The pre-compacted billets were deformed by HPT (high pressure torsion), and then the deformed billets were observed microstructure and magnetic properties. After the HPT process at room temperature, the grain size decreased with increasing because of the melted Nd-rich phase, and the anisotropy of Nd₂Fe₁₄B phase was formed after the HPT process.

• Proceedings of the KIEE Conference
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• 2008.11a
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• pp.285-286
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• 2008

The Gas Circuit Breaker for the Main Transformer of voltage, 154kV at the ist Hapcheon hydraulic power station, break down by the falling of a thunderbolt from now, let's improve the efficiency on the maintenance of generating equipment by studying about the cause and the method for this problem.