• Proceedings of the KIEE Conference
• /
• 2003.07a
• /
• pp.323-325
• /
• 2003

A current differential relay may maloperate for external faults with CT saturation and requires an additional method to cope with the problem. This paper proposes a current differential relaying algorithm for transmission line protection using an advanced compensation algorithm of the secondary current of CTs. The compensation algorithm is unaffected by a remanent flux. The proposed algorithm does not need an additional method for CT saturation and thus can achieve high stability for an external fault.

• Proceedings of the KIPE Conference
• /
• 2001.07a
• /
• pp.231-234
• /
• 2001

The torque of SRM depends on phase current and the derivative of inductance. But the inductance of SRM is nonlinearly changed according to rotor position angle and phase current because of saturation in magnetic circuit. Therefore this has a concern in torque ripple and speed variation, and it is difficult to control the desired torque The torque of SRM depends on phase current and the derivative of inductance. But the inductance of SRM is nonlinearly changed according to rotor position angle and phase current because of saturation in magnetic circuit, and it is difficult to control the desired torque. This paper proposes an optimization control scheme by adjusting both the turn-on and turn-off angle according to high efficiency points which are simulated by GA-Neural Network, which is used to simulate the reasonable switching angle which is nonlinearly varied with rotor speed and load.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.11 no.4
• /
• pp.340-348
• /
• 2006

This paper proposes an inrush current control technique of matching transformer for configuration of dynamic voltage restorer(DVR). The DVR system consist of PWM inverter to inject arbitrary voltage, LC low pass filter as harmonic eliminator and matching transformer for isolation. However, the matching transformer has an excess of inrush current by magnetic flux saturation in the core. Due to this inrush current, the rating of matching transformers is double for needed nominal rating for protection of DVR. Therefore, in this paper, the modeling method of magnetic flux saturation is used to analyze a magnitude of inrush current, and additional current controller is used for PWM inverter output regulation. Simulation and experimental results are provided to demonstrate the validity of the proposed control method.

• Journal of Korean Physical Therapy Science
• /
• v.10 no.1
• /
• pp.38-46
• /
• 2003

Since the current tendencies show us the increasing number of cerebral palsy children and the standard longevity, we need to find out more research about the following various problems. Therefore I have tried to figure out the difference of oxygen saturation and heart rate between before ambulation and after. Objects chosen are 17 C.P children on the process of treatment those who were able to walk and 8 normal children in Ah-San hospital, Gang-Nung. They haven't had either any operation or suffered heart disease and I measured their oxygen saturation and heart rate by using pulse-oximeter and are analyzed by SPSS (10.07 version). Results are the followings; 1. There was no difference of oxygen saturation and heart rate between pre-ambulation and post-ambulation of normal and spastic hemiplegia children. 2. There showed the significant statistic difference of oxygen saturation, heart rate between pre-ambulates and post-ambulation of normal and spastic diplegia(p<.05). 3. There was no difference of oxygen saturation, heart rate in C.P between(p>.05), but shows the significant statistic difference in heart rate(p<.05). As I compared the oxygen saturation and heart rate of spastic and normal children on between pre-ambulation and post-ambulation, theres is significant statistic difference on both items (p<.05). However there was no difference of oxygen saturation among hemiplegia, normal and diplegia children while the pulse rate showed the significant difference(p<.05). According to this clinical research, CP children's oxygen saturation and heart rate had no change between pre and post compared to normal children. But there was difference in diplegia. This is why we need to invest time to study these kinds of research about various analysis and comparison of oxygen saturation and heart rate, and furthermore making use of pulse-oxymetry in physical therapy room for the children involved would be beneficial to calculate in accuracy without any discomfort for the patient as well.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.3 no.1
• /
• pp.61-69
• /
• 1998

In this paper, discrete current control of voltage source inverters is proposed. As a current control scheme, the constant switching frequency predictive current control is adopted and implemented with DSP microprocessor system. In particular, the proposed method is for the compensation of the control lagging due to calculation delays in the microprocessor controller. In controlling the current, the inverter output voltage saturation problem is inevitable and usually affects the current control performance. So, the saturation boundary condition of the inverter output voltage and its effects on the current controal performance of the proposed current control scheme are investigated with experiment. Finally, the proposed scheme is applied to the active power filter system and some results are described for validation.

• Progress in Superconductivity and Cryogenics
• /
• v.11 no.1
• /
• pp.30-34
• /
• 2009

This paper deals with charging and persistent-current mode operating characteristics of BSCCO magnet load using high-temperature superconducting (HTS) power supply. The HTS power supply consists of two heater-triggered switches, an iron-core transformer with the primary copper winding and the secondary BSCCO solenoid, and a BSCCO magnet load. The magnet load was fabricated by double pancake winding and its inductance is about 21 mH. A hall sensor was installed at the middle of the magnet load to measure the current in the load. In order to investigate the efficient pumping characteristics, operating tests of heater-triggered switch with respect to dc heater current were carried out, and the electromagnet current was determined by considering saturation characteristics of its iron core. The saturation characteristics of charged current in the magnet load were observed with respect to various pumping periods: 12 s, 14 s, 24 s and 32 s. After charging the magnet load, the persistent current was measured. The operating characteristics of the persistent current mode were mainly determined by joint resistance and magnet load.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.905-908
• /
• 2001

The microstructure and the magnetic properties of Mn-Zn ferrite, which were power loss and saturation magnetic flux density, were investigated as the function of the process before firing. The highest initial permeability and the lowest power loss were attained to the specimen with CaO 400 ppm as a resulted from the highest solubility to SiO$_2$and the creation of liquid phase which improved sintering. The biggest grain size, the highest saturation magnetic flux density and the lowest power loss, which was resulted from that the eddy current loss increased as grain size increased but the hysteresis loss much more decreased and the hysteresis loss strongly influenced on the total power loss rather than the eddy current loss, were obtained to the Mn-Zn ferrite added 2wt% PVA. The power loss was lowest and the saturation magnetic flux density was highest in case of 1 ton/$\textrm{cm}^2$ and the grain size was not influenced.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.4 no.2
• /
• pp.50-56
• /
• 2008

The tubes in heat exchanger are typically made of copper alloy, stainless steel, carbon steel, titanium alloy material. Type-439 ferritic stainless steel is ferromagnetic material, and furnish higher heat transfer rates than austenitic stainless steels and higher resistance to corrosion-induced flaws. Ferritic stainless steel can be found in low-pressure(LP) feedwater heaters and moisture separator reheaters(MSRs) in turbine system. LP feedwater heaters generally utilize thin wall Type-439 stainless steel tubing, whereas MSRs typically employ a heavier wall tubing with integral fins. Service-induced damage can occur on the O.D(outside diameter) surface of Type-439 ferritic stainless steel tubing which is employed for MSRs tubing, and the most typical damage mechanism is vibration-induced tube-to-TSP(tube support plate) wear and fatigue cracking. The wear has been reported that occurs mainly on the OD surface. Accordingly, in this study, we have evaluated the flaw sizing capability of magnetic saturation eddy current technique using magnetic saturation probe and flawed specimen.

• Transactions on Electrical and Electronic Materials
• /
• v.18 no.2
• /
• pp.97-102
• /
• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07a
• /
• pp.392-395
• /
• 2003

For the first time, the new dual trench gate Emitter Switched Thyristor is proposed for eliminating snap-back effect which leads to a lot of serious problems of device applications. Also, the parasitic thyristor that is inherent in the conventional EST is completely eliminated in the proposed EST structure, allowing higher maximum controllable current densities for ESTs. Moreover, the new dual trench gate allows homogenous current distribution throughout device and preserves the unique feature of the gate controlled current saturation of the thyristor current. The conventional EST exhibits snap-back with the anode voltage and current density 2.73V and $354/{\S}^2$, respectively. But the proposed EST exhibits snap-back with the anode voltage and current density 0.93V and $58A/{\S}^2$, respectively. Saturation current density of the proposed EST at anode voltage 6.11V is $3797A/{\S}^2$. The characteristics of 700V forward blocking of the proposed EST obtained from two dimensional numerical simulations (MEDICI) is described and compared with that of the conventional EST.