• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.3
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• pp.158-164
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• 2003

This paper proposes a percentage current differential relaying algorithm for bus protection using an advanced compensating algorithm of the secondary current of current transformers (CTs). The compensating algorithm estimates the core flux at the start of the first saturation based on the value of the second-difference of the secondary current. Then, it calculates the core flux and compensates distorted currents using the magnetization curve. The algorithm Is unaffected by a remanent flux. The simulation results indicate that the proposed algorithm can discriminate internal faults from external faults when the CT saturates. This paper concludes by implementing the algorithm into a TMS320C6701 digital signal processor. The results of hardware implementation are also satisfactory. The proposed algorithm can improve not only stability of the relay in the case of an external fault but sensitivity of the relay in the case of an internal fault.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.308-310
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• 2003

This paper proposes a percentage current differential relaying algorithm for bus protection with a compensation algorithm of a CT. The compensating algorithm estimates the core flux at the start of the first saturation based on the value of the third-difference of the secondary current. It calculates the core flux and compensates distorted currents in accordance with the magnetization curve. The test results indicate that the algorithm can discriminate internal faults from external faults when the CT saturates. It can improve not only stability of the relay in the case of an external fault but sensitivity of the relay in the case of an internal fault.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.8-13
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• 2011

A percentage current differential relay is widely used for transformer protection. Because many percentage current differential relays recently use modified methods instead of conventional methods for deciding the operating characteristics of the large current region, in this paper, the operating region of a percentage current differential relay is analyzed in input-output current domain instead of operating-restraint current domain. An effective method to set the operating region when a CT is saturated is proposed with a series of investigations comparing a conventional method with the proposed modified method. The performance of the proposed method is evaluated for internal and external faults of a power transformer having the voltage rating of 345/154kV. EMTP-RV is used for the relaying data collection.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.157.2-157
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• 2001

This paper describes the synergism of Artificial Neural Network and Fuzzy Logic based approach to improve the reliability of transformer differential protection, the conventional transformer differential protection commonly used a harmonic restraint principle to prevent a tripping from inrush current during initial transformer´s energization but such a principle can not performs the best optimization on tripping time. Furthermore, in some cases there may be false operation such as during CT saturation, high DC offset or harmonic containing in the line. Therefore an artificial neural network and fuzzy logic has been proposed to improve reliability of the transformer protection relay. By using EMTP-ATP the power transformer is modeled, all currents flowing ...

• Geosystem Engineering
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• v.21 no.6
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• pp.344-351
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• 2018

It is reported that the flooding rate in low permeability sandstones is low and the oil recovery is hard to increase after water breakthrough. Understanding characteristics of waterflood is hence important for the recovery improvement. In this work, flooding tests on low permeability sandstones were conducted. The corresponding flooding characteristics were investigated by means of CT scanning and Nuclear Magnetic Resonance. Effects of irreducible water and different rates were also discussed in detail. Experimental results reveal a piston-like displacement at a low rate in low permeability samples. The saturation profile is steep and almost vertical to the forward direction. The results at a low rate confirm that once water broke through, increasing the flooding rate or flooding time can hardly reduce the remaining oil inside the sample. It is probably due to the high pore-throat ratio proven by rate-controlled mercury. Results also confirm that the presence of initial water enhanced sweep efficiency substantially. On one hand, because water had previously occupied the small pores, the subsequent oil can only invade relatively large pores and became more movable. On the other hand, stable collars can not form due to the steep front, which may suppress the snap-off.

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.85-91
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• 2018

Computed tomography, which obtains section images from reconstruction process using projection images, has been applied to various fields. The spatial resolution of the reconstructed image depends on the device used in CT system, the object, and the reconstruction process. In this paper, we investigates the effect of the number of projection images and the pixel size of the detector on the spatial resolution of the reconstructed image under the parallel beam geometry. The reconstruction program was written in Visual C++, and the matrix size of the reconstructed image was $512{\times}512$. The numerical bar phantom was constructed and the Min-Max method was introduced to evaluate the spatial resolution on the reconstructed image. When the number of projections used in reconstruction process was small, artifact like streak appeared and Min-Max was also low. The Min-Max showed upper saturation when the number of projections is increased. If the pixel size of the detector is reduced to 50% of the pixel size of the reconstructed image, the reconstructed image was perfectly recovered as the original phantom and the Min-Max decreased as increasing the detector pixel size. This study will be useful in determining the detector and the accuracy of rotation stage needed to achieve the spatial resolution required in the CT system.

• The Korean Journal of Nuclear Medicine Technology
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• v.12 no.3
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• pp.214-221
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• 2008

Purpose: We make a qualitative analysis of whether Fusion SPECT/CT can find lesion's anatomical sites better than existing SPECT or not, and we want to show the usefulness of SPECT/CT through finding out effects of CT attenuation correction on SPECT images. Materials and Method: 1. The evaluation of fusion images: This study comprised patients who was tested $^{131}I$-MIBG, Bone, $^{111}In$-Octreotide, Meckel's diverticulum, Parathyroid MIBI with Precedence 16 or Symbia T2 from 2008 Jan to Aug. We compared SPECT/CT image with non fusion image and make a qualitative analysis. 2. The evaluation of attenuation correction: We classified 38 patients who was tested 201Tl myocardial exam with Symbia T2 into 5 sections by using Cedars Sinai' QPS program - Ant, Inf, Lat, Septum, Apex. And we showed each section's perfusion states by percentage. We compared the each section's perfusion-states differences between CT AC and Non AC by average${\pm}$standard deviation. Results: 1. The evaluation of fusion images : In high energy $^{131}I$ cases, it was hard to grasp exact anatomical lesions due to difference between regions and surrounding lesions' uptake level. After combining with CT, we could grabs anatomical lesion more exactly. And in meckel's diverticulum case or to find lesions around bowels or organs with $^{111}In$ cases, it demonstrates its superiority. Bone SPECT/CT images help to distinguish between disk spaces certainly and give correct results. 2. The evaluation of attenuation correction: There is no significant difference statistically in Ant and Lat (p>0.05), but there is a meaningful difference in Inferior, Apex and Septum (p<0.05). AC perfusion at inferior wall in the 5 sections of myocardium: The perfusion difference between Non AC perfusion image ($68.58{\pm}7.55$) and CT corrected perfusion image ($76.84{\pm}6.52$) was the largest by $8.26{\pm}4.95$ (p<0.01, t=10.29). Conclusion: Nuclear medicine physicians can identify not only molecular image which shows functional activity of lesions but also anatomical location information of lesions with more accuracy using the combination of SPECT and CT systems. Of course this combination helps nuclear medicine physician find out the abnormal parts. Moreover combined data sets help separate between normal group and abnormal group in complicated body part. So clinicians can carry out diagnosis and treatment planning at the same time with a single test image. In addition, when we examine a myocardium in thorax where attenuation can occur easily, we can trust perfusion more in a certain region in SPECT test because CT provides the capability for accurate attenuation correction. In these reasons, we think we can prove the justice after treatment fusion image.

• The Korean Journal of Food And Nutrition
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• v.11 no.1
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• pp.6-10
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• 1998

It was determined to effects on cold test(CT) and smoke point (SP) of deodorizing temperature(DT) in corn oil. Increase of DT was induced to decrease of CT in deodorized oil, which was against the winterized oil inleted. Especially, the decrease of CT in deodorized oil was sharply at more than 26$0^{\circ}C$, this phenomenon was supposed to according the increase of total saturation degree as well as SU2, S2U, and S3 type triglyceride content. On the other hand, SP was showed the highest value as 242$^{\circ}C$ at DT as 24$0^{\circ}C$, the value was decreased to 235~238$^{\circ}C$ at DT as 245~27$0^{\circ}C$. This phenomenon was appeared in inverse proportion to the acid value of sample oils. Accordingly, high temperature deodorizing proved to be a very undesirable effect between general physicochemical characteristics, fatty acid composition and CT, SP etc.

• Journal of Trauma and Injury
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• v.33 no.2
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• pp.88-95
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• 2020

Purpose: The present study will identify risk factors for aspiration in severe trauma patients by comparing patients who showed a sign of aspiration lung disease on chest computed tomography (CT) and those who did not. Methods: We conducted a retrospective review of the Korean Trauma Data Bank between January 2014 and December 2019 in a single regional trauma center. The inclusion criteria were patients aged ≥18 years with chest CT, and who had an Injury Severity Score ≥16. Patients with Abbreviated Injury Scale (AIS)-chest score ≥1 and lack of medical records were excluded. General characteristics and patient status were analyzed. Results: 425 patients were included in the final analysis. There were 48 patients showing aspiration on CT (11.2%) and 377 patients showing no aspiration (88.7%). Aspiration group showed more endotracheal intubation in the ER (p=0.000) and a significantly higher proportion of severe Glasgow Coma Scale (GCS) (p=0.000) patients than the non-aspiration group. In AIS as well, the median AIS head score was higher in the aspiration group (p=0.046). Median oxygen saturation was significantly lower in the aspiration group (p=0.002). In a logistic regression analysis, relative to the GCS mild group, the moderate group showed an odds ratio (OR) for aspiration of 2.976 (CI, 1.024-8.647), and the severe group showed an OR of 5.073 (CI, 2.442-10.539). Conclusions: Poor mental state and head injury increase the risk of aspiration. To confirm for aspiration, it would be useful to perform chest CT for severe trauma patients with a head injury.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.55-59
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• 1991

The temperature-dependent magnetization curves of amorphous Fe-Co-(Nd, Sm, Gd, Tb)-B alloys were measured using a vibrating sample magnetometer from 77 K up to 900 K. The spin wave stiffness constants and the range of the exchange interaction were calculated from the saturation magnetization values at 0 K. Curie temperatures and the Bloch coefficients estimated from the saturation magnetization curves. The low temperature dependence of magnetization is in good agreement with Bloch relation, $M_{s}(T)=M_{s}(O)(1-BT^{3/2}-CT^{5/2})$. The spin wave stiffness constant and the range of exchange interaction are decreased by substitution of heavy rare earth (Tb, Gd).