• 전기학회논문지
• /
• 제60권1호
• /
• pp.8-13
• /
• 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.

• Journal of Electrical Engineering and Technology
• /
• 제12권2호
• /
• pp.665-673
• /
• 2017

This paper proposes a field weakening control method for operating an induction motor with a variable DC input voltage condition. In the variable DC voltage condition such as a battery, the field weakening method are required for the maximum output power. The conventional field weakening control methods can be used for operating the induction motor over the rated speed in a constant DC-link voltage condition. However, the conventional methods for operating the motor with the variable DC voltage is not suitable for the maximum output power. To overcome this problem, this paper proposes the optimized field weakening control method to extend the operating range of the induction motor with a rated power in a limited thermal and a wide DC input voltage conditions. The optimized d-axis and q-axis current equations are derived according to the field weakening region I and II to extend the operating region. The experimental results are presented to verify the effectiveness of the proposed method.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 B
• /
• pp.709-711
• /
• 1999

In this paper, Fuzzy Logic Controller was Designed for the Degree control of Arago's disk system. Arago's disk system is an application of Arago's disk phenomenon which is the operating principle of induction motor. Since the Arago's disk system varies to stable region. maginally stable region, unstable region according to the degree of bar respectively, it is a sutable system which can be evaluate an efficiency of the system. While an existing controller which was designed using linearized system modeling could control the system on only one operating point, fuzzy logic controller has the advantage in showing good response for multi-operating points because it does not need system modeling.

• 한국통신학회논문지
• /
• 제28권3A호
• /
• pp.185-191
• /
• 2003

본 논문에서는 문턱 전압의 감소에 의해 넓은 동작 영역을 갖는 새로운 구조의 트랜지스터를 제안하였다. 문턱 전압을 감소시키기 위해 제안된 복합 트랜지스터Ⅰ은 P형 폴디드(P-type folded) 복합 트랜지스터를 이용하였고, 복합 트랜지스터Ⅱ는 제너 다이오드를 이용하였다. 제안된 트랜지스터가 전류원에 의해 동작 영역이 제한되는 현상을 고찰하여 검증하였으며, 제안된 회로들은 0.25㎛ CMOS n-well 공정 파라미터를 이용하여 2.5V 공급 전압하에서 Hspice 시뮬레이션을 통해 그 특성을 검증하였다.

• Journal of Power Electronics
• /
• 제19권3호
• /
• pp.761-770
• /
• 2019

This paper proposes a hybrid phase windings excitation method for improving the efficiency of a 7-phase brushless DC (BLDC) motor in the electric propulsion system of a ship. The electrical losses of a BLDC motor system depend on the operating region and the number of excited phase windings (2-phase, 4-phase or general 6-phase windings). In this paper the operating region and torque/speed characteristics according to the motor rotation speed and propeller load are analyzed for a number of excitation methods. In addition, it analyzes the electrical losses of the system under each of the excitation methods in the entire operating region of the motor. In every sampling time, the proposed control method calculates the electrical loss of the system for each of the excitation methods and operates a 7-phase BLDC motor by selecting the excitation method that results a decreased electrical loss at the operating speed. The usefulness of the proposed control algorithm is verified through experimental results.

• 한국멀티미디어학회논문지
• /
• 제6권1호
• /
• pp.78-88
• /
• 2003

본 논문에서는 연산 영역 가변 알고리즘을 적용한 MPEG-4 부호화 기반의 적응적 오류 은닉 (error concealment) 기법을 제안하였다. 이 알고리즘에서는 손실 블록을 그의 주변 정보를 이용하여 이들을 평탄블록 (flat block) 및 에지 블록 (edge block)으로 분류한다. 즉, 손실된 블록의 주변 블록들에 대해서 블록 경계 영역의 인접 화소들의 차를 이용하여 평탄 블록을 분류하고, 평탄 블록으로 분류되지 않은 블록들에 대해서는 인접 화소의 차가 정해진 임계값을 넘어서는 개수에 따라 가변적인 연산 영역 (variable operating region, VOR)을 설정한 후, Sobel 연산자를 적용하여 우세 에지 방향 성분을 추정한다. 이렇게 분류된 각 블록에 대하여 적응적 오류 은닉을 수행한다. 평탄 블록에 대해서는 시각적 성능 향상을 위해 평균값을 기반으로 한 가중치에 따른 양선형 보간(mean based weighted bilinear interpolation, MWBLI) 방법을 적용하고, 에지 블록에 대해서는 8가지 방향에 대하여 경계 픽셀을 이용한 방향성 보간 (boundary directional interpolation, BDI) 방법을 적용하여 오류 은닉을 수행한다. 모의 실험 결과를 통하여 제안한 방법이 객관적 화질 및 주관적 화질 측면에서 기존의 방법보다 그 성능이 우수함을 확인하였다.

• 한국유체기계학회 논문집
• /
• 제14권4호
• /
• pp.19-24
• /
• 2011

An experimental study was conducted to examine the effectiveness of a suction-blowing fan that could not only remove polluted air by suction but also create the air-curtain by blowing. In order to create the air-curtain, rotors were installed on the surface of the shroud. These blows fresh air into the polluted region. The fresh air is spouted backward 45o on the basis of the axial direction using a double-ducted bellmouth. In the same suction operating condition, the suction region was extended by increasing the blowing velocity. However, the increasing rate of suction region was reduced when the blowing velocity was increased steadily. Thus, an efficient blowing velocity should be determined depending on the suction operating condition. In addition, the blowing requires additional input power. In a fixed suction operating condition, the input power was linearly increased in proportion to the blowing flowrate. When the suction-blowing fan was operated in the same input power as the suction fan, the suction region was increased more than 30% based on the 0.6m/sec velocity.

• 동력기계공학회지
• /
• 제13권2호
• /
• pp.30-35
• /
• 2009

Numerical Calculations for dimensionless pressure drop (friction factor times Reynolds number) have been obtained for fully developed laminar flow of MPL(Modified Power Law) fluid in isosceles triangle pipes. The solutions are valid for Pseudoplastic fluids over a wide range from Newtonian behavior at low shear rates through transition region to power law behavior at higher shear rates. The analysis identified a dimensionless shear rate parameter which for a given set of operating conditions specifies where in the shear rate range a particular system is operating, i.e., Newtonian, transition or power law region. The numerical calculation data of the dimensionless pressure drop for the Newtonian and power law regions are compared with previously published asymptotic results presenting within 0.16 % in Newtonian region and 2.98 % in power law region.

• 한국소음진동공학회논문집
• /
• 제20권5호
• /
• pp.502-509
• /
• 2010

A test facility which can simultaneously measure turbocharger operating condition variables and vibro-acoustic emission in the situations that are quite similar to real internal combustion engine operating conditions has been introduced. Using this facility, a new method sweeping from full open throttle to deep surge region along constant speed curves can be utilized instead of the stationary method that has been traditionally used to obtain turbocharger compressor maps. Data covering an extensive range of the compressor performance map have been collected and analyzed. An experimental study is performed to define a noise diagram that correlates vibro-acoustic measurements to aerothermodynamic operating conditions. An instrumentation set in the facility allows the automatic definition of the operating point on the turbine and compressor map of the turbocharger. Also, radiated sound pressure and casing vibration data corresponding to the point are obtained by a microphone in the vicinity of the compressor casing and an accelerometer on the casing. The major source(s) of noise at specific operating point on the map can be easily identified with these maps. Also, acoustic characteristics of a given turbocharger at the vicinity of the surge as well as in the surge are also defined. Finally, the possibility to define mild surge region of a turbocharger using vibro-acoustic measurements is studied.

• 한국콘텐츠학회논문지
• /
• 제12권3호
• /
• pp.181-189
• /
• 2012

본 연구는 수도권 소재 문화예술회관의 지역별 운영주체별 효율성을 분석한 것이다. 최근 문화산업의 중요성은 커지고 있다. 또한 지역문화산업의 근간으로 문화예술회관의 중요성이 부각되었다. 따라서 문화 산업의 활성화를 위해 문화예술회관의 운영상에 효율성을 재고하여야 한다. 문화예술회관을 객관적으로 분석하기 위해 공공기관 효율성 분석도구인 DEA를 이용하였으며, 이는 운영효율성에 초점을 맞춘 것이다. 분석 결과에 따라 서울, 인천, 경기도의 효율성을 확인할 수 있었다. 또한 직접운영기관, 공단운영기관, 재단법인기관, 민간위탁기관의 효율성이 나타내는 특징을 확인 할 수 있었다. 지역별로 살펴보면 서울과 경기도 소재의 기관이 효율적으로 운영되는 것을 알 수 있다. 반면, 인천 소재의 문화예술회관은 효율적이지 않았다. 운영주체별로 살펴보면, 직접운영기관과 공단운영기관은 효율적으로 운영되었다. 반면에, 재단법인기관과 민간위탁기관은 상대적으로 비효율적으로 운영되었다.