• International Journal of Air-Conditioning and Refrigeration
• /
• 제12권3호
• /
• pp.148-157
• /
• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^{2}s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C\;to\;15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations un-derpredict the low mass flux and overpredict the high mass flux data.

• 조명전기설비학회논문지
• /
• 제26권2호
• /
• pp.92-98
• /
• 2012

As the increasing of non-linear load, filter is coming to be high gradually in order to reduce the harmonic which occurs from the power conversion. The maintenance of passive filter is easier than active filter and it has been widely used in the industrial site. This passive filter is connected with condenser and reactor by series and parallel and it is installed at the front of nonlinear load. The breakdown of passive filter occurs frequently at the reactor side rather than capacitor. So the breakdown cause close examination is necessary. In this paper, we analyzed that the electric stress of reactor which is considered magnetization saturation at the passive filter. We confirm that the reduction of harmonics and the electric stress of reactor is influenced by the linear and non-linear element of reactor.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1991년도 하계학술대회 논문집
• /
• pp.247-250
• /
• 1991

In this paper, we have investigated the poling conditons depending upon the electric field and temperature for PZT ceramics with various stoichiometry prepared by wet direct method, and $MnO_2$ dopant. The electric field required for saturation polarization was plotted against temperature $(1,000/T^{\circ}K)$ so that the required field could be estimated at any given temperature by measuring the charge displaced during poling. From this curve it should be possible to predict the field required to produce maximum domain switching at temperature below the Curie temperature, when $MnO_2$ dopant was added to the PZT ceramics, the electric field required for saturation polarization was lowered than that of undoped PZT samples.

• 조명전기설비학회논문지
• /
• 제26권8호
• /
• pp.65-70
• /
• 2012

Induction motor is the most widely used to obtain the driving force in the industrial site. Induction motor generates a high current at startup. Most of starting currents are often more than five times of rated current. This high starting current can cause problems such as the voltage drop in the system. In order to solve these problems, if the motor capacity is large, generally we use reactor starting method rather than direct on line starting method. When a high startup current passes through reactor, reactor can serve as a nonlinear elements. In this study, we analyzed that the current, torque and power of the induction motor are different from the change of linear and nonlinear components of the reactor magnetic field.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.649-655
• /
• 2010

Unsaturated compressive tests are performed to evaluate the effect of matric suction on the strength and the deformation characteristics for statically compacted natural kaolin in Korea. Under different conditions of the initial degree of saturation in kaolin, the relationship between suction and the degree of saturation at failure can be expressed by unique soil-water characteristic curve. These results demonstrate that the newly established constant water content type unsaturated shear strength test equipment can be used for estimating the relationship between suction and the compressive strength.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 A
• /
• pp.213-215
• /
• 2002

This paper proposes an advanced compensating algorithm of the secondary current of CTs. The exiting compensating algorithm for the current transformers calculates magnetic flux using the magnetization curve. In such a case, it is difficult to compensate for distorted secondary current when a remanent flux exists in a core at the beginning of the calculation. To make up for the drawback in the existing compensating algorithm, the algorithm detects the instant of saturation using difference of the secondary current and estimates flux at the instant of the beginning of the first saturation. After that, the algorithm calculates flux and compensates for distorted secondary current.

• Journal of Electrical Engineering and Technology
• /
• 제1권4호
• /
• pp.482-489
• /
• 2006

This paper presents the generalized dynamic modeling of self-excited induction generator (SEIG) using state-space approach. The proposed dynamic model consists of induction generator; self-excitation capacitance and load model are expressed in stationary d-q reference frame with the actual saturation curve of the machine. An artificial neural network model is implemented to estimate the machine magnetizing inductance based on the knowledge of magnetizing current. The dynamic performance of SEIG is investigated under no load, with the load, perturbation of load, short circuit at stator terminals, and variation of prime mover speed, variation of capacitance value by considering the effect of main and cross-flux saturation. During voltage buildup the variation in magnetizing inductance is taken into consideration. The performance of SEIG system under various conditions as mentioned above is simulated using MATLAB/SIMULINK and the simulation results demonstrates the feasibility of the proposed system.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 B
• /
• pp.628-630
• /
• 1995

CT saturation may cause protective relays to malfunction. The conventional method to deal with the problem is overdimensioning of the core so that CTs can carry up to 20 times the rated current without exceeding 10 % ratio correction. However, this not only reduces the sensitivity of relays, but also increases the CT core size. This paper presents a technique of estimating the secondary current corresponding to the CT ratio under CT saturation using the magnetization curve. The proposed algorithm can improve the sensitivity of relays to low level faults and minimize the instability of relays for external faults.

• 대한전기학회논문지:전력기술부문A
• /
• 제52권3호
• /
• pp.158-164
• /
• 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.

• 대한전기학회논문지
• /
• 제45권4호
• /
• pp.501-510
• /
• 1996

The gas-turbine generator of Seo-Incheon combined-cycle plant was tested for derivation of a model for dynamic analysis. Load rejection and AVR step test was performed to get the dynamic response of generator. The parameters of generator/control system model were determined by these measured data. No-load saturation test was performed for the saturation characteristics of the generator under steady state. V-curve test was also performed so as to find exact generator parameters. Q-axis parameters of generator was derived by measuring power angle. AVR and governor constants have been tuned by their oscillatory period and setting time characteristics. The derived parameters of generator control system is verified by one-machine infinite bus system simulation. (author). 7 refs., 20 figs., 5 tabs.