• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1644-1651
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• 2010

VLF $tan{\delta}$ diagnosis technology is introduced in IEEE Std 400 and proposed as evaluation criterion in an effective way of detecting water tree which mainly causes the failure of XLPE insulated cables. In order to inspect the accuracy of the VLF $tan{\delta}$ method for XLPE insulated power cables in Korean distribution system, diagnosis for 41 cables which were being serviced in the fields has been carried out and they were removed for AC breakdown voltage test after. Regarding the 41 cables, it was hard to confirm any relation between the VLF $tan{\delta}$ values and AC breakdown voltages and also water tree in the insulation was not detected. However, the other cables were failed several days after the diagnosis of the 41 cables. Water trees were found and their VLF $tan{\delta}$ values were also much higher than the criterion of IEEE standard. It has been ascertained that we need to change the IEEE criteria in order to improve the accuracy of detecting water trees by additional analyzing of field examples of failure and case studies from overseas countries and therefore amended VLF $tan{\delta}$ test voltage and evaluation criteria have been proposed.

• Geomechanics and Engineering
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• v.29 no.5
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• pp.523-533
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• 2022

Several prediction model of penetration rate (PR) of tunnel boring machines (TBMs) have been focused on applying to design stage. In construction stage, however, the expected PR and its trends are changed during tunneling owing to TBM excavation skills and the gap between the investigated and actual geological conditions. Monitoring the PR during tunneling is crucial to rescheduling the excavation plan in real-time. This study proposes a sequential prediction method applicable in the construction stage. Geological and TBM operating data are collected from Gunpo cable tunnel in Korea, and preprocessed through normalization and augmentation. The results show that the sequential prediction for 1 ring unit prediction distance (UPD) is R²≥0.79; whereas, a one-step prediction is R²≤0.30. In modeling algorithm, a gradient boosted regression tree (GBRT) outperformed a least square-based linear regression in sequential prediction method. For practical use, a simple equation between the R² and UPD is proposed. When UPD increases R² decreases exponentially; In particular, UPD at R²=0.60 is calculated as 28 rings using the equation. Such a time interval will provide enough time for decision-making. Evidently, the UPD can be adjusted depending on other project and the R² value targeted by an operator. Therefore, a calculation process for the equation between the R² and UPD is addressed.

• Journal of Forest and Environmental Science
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• v.35 no.3
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• pp.197-204
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• 2019

A tree-length harvesting system using the HAM300, which is mounted on a farm tractor prototype machine, have been recently introduced in South Korea for thinning old (>30 years) forests. However, no research has previously been conducted on the characteristics of residual stand damage associated with cable yarding systems on thinning treatment stands in South Korea. Therefore, there were assessed on the degree and quantity of residual stand damage caused by felling and yarding process to broaden the knowledge of residual stand damage on semi-mechanized skyline thinning operations. This study investigated scar size, direction, area, shape type and their distribution on the residual stand damage caused by felling and yarding operations. Damage to residual trees was generated for 7.4% and 6.9% of residual trees in felling and yarding operations, respectively. Damaged direction of scars was located in front-side (38.9%) and up-side (34.7%) for felling operations while the highest scar damage was found on down-side (44.6%) for yarding operations. Scar heights of felling damage were higher than those of yarding damage. In yarding operation, the most of the scars was located within l0m from the center of the skyline corridor. These results should be useful information for forest managers and landowners to reduce residual stand damages and retain valuable timber volume from thinning treatments.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.2
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• pp.75-80
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• 2006

In this paper, to detect and observation the void discharges pulse signal, AE signals and tree growth characteristics in case the high voltage is applied to a XLPE sample for a power cable. We also examined the partial discharge current pulse and AE signals with the increase of the applied voltage in XLPE insulation. The experimental results show that a branch-type tree grows in the presence of the voids, and a bush-type tree grows in the absence of the voids in both samples. A rate of tree growth increases abruptly in proportional to the deterioration time in the presence of the of the voids, but in the absence of the voids, a rate of tree growth decreases as time goes by and finally a breakdown occurs. The frequency band of AE signals that are generated from the partial discharges in a XLPE sample, one of solid dielectric materials, is about 1.0[MHz].

• Journal of Korean Society of Forest Science
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• v.105 no.2
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• pp.231-237
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• 2016

This research was conducted in order to examine whether the Woodgrab short-wood logging method, most widely used logging method in Korea, is more favorable than other logging methods in terms of productivity and profitability. For the comparative purposes, whole-tree logging methods with cable yarding system using a swing yarder and a tower yarder were evaluated. The productivity and the profitability of the logging operations by the machine types on a L. kaempferi stand were estimated by simulating logging processes based on bucking patterns and the results were compared. As a result, the Woodgrab short-wood logging system showed the most favorable results in terms of skidding productivity and operating cost. On the contrary, the system was the least profitable among the three logging methods. Main reason is that while the system may be beneficial in terms of operation productivity, it is restricted to produce only short logs mainly for low quality raw materials such as pulp, bolts, etc. which are sold at cheap prices.

• Journal of Korean Society of Forest Science
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• v.108 no.4
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• pp.562-573
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• 2019

In a cable yarding system, a small-scale tower yarder attached to a farm tractor wasdeveloped and used for small-diameter tree harvesting operations. Based on this design, improvement of traction performance was required for medium- and large-diameter tree harvesting operations. In this study, the mechanical transmission employed for the tower yarder was modified into ahydro-mechanical transmission system. Maximum traction forces, including tractor engine speed and hydraulic power pressure, were investigated, and comparisons were made between the mechanical and hydro-mechanical transmission systems. Six tractor engine speeds (1,200, 1,400, 1,600, 1,800, 2,000, and 2,200) and three levels of power transmission mechanism pressure (4.9, 6.9, and 8.8 MPa) were investigated in the two different transmission systems. Results showed a maximum traction force of 15,146.6 N at an engine rotation speed of 757 rpm in the current mechanical transmission system, and 36,140.0 N at anengine rotation speed of 1,575 rpm in the modified hydro-mechanical transmission system. The maximum traction forces for the hydro-mechanical transmission were 2.4 times greater than those of the mechanical transmission, and may therefore be applicable to medium and large-diameter tree harvesting operations. Thus,as a modified version of the conventional transmission system, the new hydro-mechanical transmission system may be cost-effective for use in large-scale cable yarding operations. In the future, however, it will be necessary to investigate problems that may arise from field application tests.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.3
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• pp.45-50
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• 1998

This paper presents experimental results on the application of very low frequency(VLF) voltage to replace conventional DC test as an after laying test for underground distribution cables. We carried out several tests to prove defects detecting ability of VLF test on the 5m length real cables having knife-cut or needle type defects which is made in our La.. Through this experiment we proved it is very difficult to initiate electrical tree from the defects inside of the cable insulation but once the electrical tree is initiated it grows very fast and VLF does not make new defects and expand the defect. Therefore VLF test equipment for quality inspection test of manufacture is more effective than field application for underground distribution cables.

• Journal of the military operations research society of Korea
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• v.36 no.3
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• pp.83-93
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• 2010

In this paper, we propose a new expert system for close combat in military war game model for training. Simulation logic for damage assesment is one of the main simulation functions in military war game. In Changcho 21's model which is the war game model for Republic of Korea Army corps and division, the main function of close combat's damage assessment has not been calculated by Changcho 21's model, but by COBRA which was made by US Army and has been the expert system for close combat. Results which were calculated in COBRA were sent to Changcho 21's model through a cable network. And Changcho 21's model finally calculated the value of damage assessment with the results. In this paper, we develop an new expert system for close combat using decision tree. The experimental results show that the proposed expert system has similar performance to COBRA and has less computing complexity. And it can substitute for COBRA and be applicable to battlefield.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1252-1260
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• 1999

The HFC network has a architecture of a star topology in fiber optic trunks, and tree and branch topology is used in the part of coaxial cable. It is well known that the HFC upstream channel is noisy. Ingress, common mode distortion and impulse noise exist in the upstream channel. In order to provide Quality of Service(QoS) to users with real-time data such as voice, video and interactive services, the evolving IEEE 802.14 standard for HFC networks must include an effective priority scheme. The scheme separates and resolves collisions between stations in a priority order. It is important to simulate protocols under a practical environment. The proposed algorithm in this paper is simulated with the assumption that the collision detector made certain mistake due to noises. Simulation results show that the proposed algorithm is more efficient than existing tree-based algorithm under practical environment.

• Proceedings of the KIEE Conference
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• 2008.09a
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• pp.6-8
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• 2008

배전케이블 수 트리 현상은 XLPE케이블의 고장을 초래하는 주요원인이다. 수 트리에 기인한 신호는 아주 미세하여 현장진단은 배경 잡음으로 인해 검출이 어렵다. 본 논문에서는 고주파특성이 우수한 L-C결합센서를 사용하여 방전신호를 측정하고 이를 주파수영역에서의 분석을 통해 현장에서 부분방전이 발생하기 훨씬 이전에 존재하는 미세신호(Pre-Discharge)를 검출하고 분석한 결과를 제시하였다. 케이블 내 수(水) 트리가가 존재하면 이것이 이종 절연물의 경계면 역할을 하석 서-지 임피던스의 차이로 인해 케이블 단자에서 발생하는 전기적 신호가 수 트리 지점에서 다수의 반사를 일으켜 그 잡음 수준을 높이는 역한을 하게 되는 것으로 알려져 있다. 만일 여러 개소에 수 트리가 존재하는 경우에는 그 배경잡음을 현저하게 높이는 결과를 보여주었다. 실험실에서 발생하는 미세 신호와 현장의 신호를 비교한 결과 아주 유사한 패턴이 있음이 파악되어 이 방법은 수 트리의 활선 진단이 가능함을 확인시켜 주었다.