• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.236-240
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• 2014

Induction motor requires a rotating magnetic for rotation. Current required to generate the rotating magnetic field is magnetizing current. This magnetizing current is associated with the reactive power. This reactive power must be supplied from source side. Therefore, the power factor of the induction motor is low. So, the capacitor is installed on the motor terminals to compensate for the low power factor. Power supply company has recommended to maintain a high power factor to the customer. If the capacitor current is greater than the magnetizing current of the motor, there is a possibility that the self-excitation occurs. So it is necessary to calculate the optimal capacity capacitor current does not exceed the magnetizing current. In this study, we first compute the no-load current and the reactive power of the induction motor and then calculates the limit of the maximum power factor without causing self-excitation.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.156-158
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• 2002

In this paper, we analyze about voltage sag effect at load side during fault according to change of power system condition. through the case studies, we find that there is no close connection between substation bus transfer and voltage sag during fault. however, we find that other feeder connecting with the faulted transmission is directly affected by fault type and magnitude, therefore, the main subject can be divided into the utility and customer side countermeasures, utilities concentrate their effort to prevent the faults and to modify the fault clearing practice in power system. however, the faults in power system can never be completely eliminated. therefore, customer side solutions usually involve the power conditioning equipment for sensitive loads aiso, we investigate that the several methods to reduce the number and severity of voltage sag and to dull the sensitivity of equipment for voltage sag have developed. moreover, about SEMI, the industry association for the semiconductor two voltage sag immunity standards.(SEMI F47, SEMI F42) The simulation is accomplished by PSS/E 26.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.5
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• pp.841-846
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• 2010

Reliability in electrical power system refers to normal operation for schedule time in some system that action consists. It means that if there is no contingency of electric power supply decrease or load curtailment, reliability of the system is high. In this paper, a method for evaluation of transmission capability is proposed considering reliability standards. Deterministic and probabilistic methods for evaluation of transmission capability has been studied. These researches considered uncertainty of system components or N-1 contingency only. However, the proposed method can inform customers and system operators more suitable transmission capability. Well-being method using state probabilities of system components proves to be a more effective method in this paper comparing with calculation of LOLE(Loss of Load Expectation). The length of calculation is shorter but it can give more practical information to the exact system operators. Well-being method is applied to IEEE-RTS 24bus system to evaluate reliability in case study. The result is compared with a existing way to evaluate reliability with LOLE and it shows that transmission capability connected with adjacent networks. This paper informs system operators and power suppliers of reliable information for operating power system.

• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.247-251
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• 2003

The developments of the hybrid energy are necessary since the future alternative energies that have no pollution and no limitation are restricted. Currently power generation system of MW scale has been developed. However, even photovoltaic system cannot always generate stable output with ever-changing weather condition. In this paper, sub power generator for hybrid system(photovoltaic 500[W], wind power generation 400[W]) was suggested. Sub power Generator that uses elastic energy of spiral spring to photovoltaic system was also added for the present system. In an experiment, when output of photovoltaic system gets lower than 24[V] (charging voltage), power was continuously supplied to load through the inverter by charging energy obtained from generating rotary energy of spiral spring operates In DC generator. Also, control algorithm of sub power generator is used genetic algorithm(GA).

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.185-187
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• 2000

Fault current is flowed into 154/23kV M. Tr when line-to-ground fault occurs in power system. NGR(Neutral Grounded Reactor) is set up in order to prevent M.Tr fault by limiting magnitude of fault currents. Here, disconnection of NGR causes voltage increase by L-C resonance and line-to-ground fault in an unearthed system results in voltage increase at healthy phases. So Over Voltage Ground Relay(OVGR) is used for tripping M.Tr. Also, buses at second phases of M.Trs are all connected with section circuit breakers closed for the purpose of parallel operation and load shedding. In case of speciality buses are comprised of power cable in part for GIS connection. When no-load charged cable or bus is open by a section CB, unbalanced voltage charged on the bus is induced. Also discrepant opening time for circuit breakers on different phases gives rise to unbalanced zero sequence voltage. It was observed that this zero sequence voltage detected in the 22.9kV P.T (Potential Transformer for bus) mal-operated 59GT and tripped M.Tr. The zero sequence voltage of which vanishing time is longer than relay operating time came out by EMTDC simulation. Also, it was shown that the voltage waves of actual test are similar to those of simulation. On the basis of above results, R-C circuit complement on the relay without any effect on a power system made operating time of the relay longer than vanishing time of distorted waves. Consequently, operating time of the relay was delayed and magnitude of distorted waves was decreased by increasing time constant of the relay.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.467-472
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• 2005

Load/Unload(L/UL) technology includes the benefits, that is, increased areal density, reduced power consumption and improved shock resistance contrary to contact start stop(CSS). It has been widely used in portable hard disk drive and will become the key technology for developing the small form factor hard disk drive. The main objectives of L/UL are no slider disk contact or no media damage. For realizing those, we must consider many design parameters in L/UL systems. In this paper, we focus on the effect of the ramp profile. We can find out the lateral velocities in L/UL process through experiments and simulations for force of voice coil motor and friction force on ramp. And then, we will gain the optimal design of ramp slope to maintain the minimum clearance of suspension dimple and slider with FE model. In special, after finding the point at which air bearing breaks and designing the ramp, we will identify the results for improving unload performance.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.204-209
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• 2005

Load/Unload(L/UL) technology includes the benefits, that is, increased areal density, reduced power consumption and improved shock resistance contrary to contact-start-stop(CSS). It has been widely used in portable hard disk drive and will become the key technology far developing the small form factor hard disk drive. The main object of L/UL is no slider-disk contact or no media damage. For realizing those, we must consider many design parameters in L/UL system. In this paper, we focus on lift-off force. The 'lift-off' force, defined as the minimum air bearing force, is another very important indicator of unloading performance. A large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. To minimize 'lift-off' force we optimizes the slider and suspension using the integrated optimization frame, which automatically integrates the analysis with the optimization and effectively implements the repetitive works between them. In particular, this study is carried out the optimal design considering the process of modes tracking through the entire optimization processes. As a result, we yield the equation which can easily find a lift-off force and structural optimization for suspension.

• Journal of the Korean Society of Combustion
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• v.19 no.3
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• pp.1-7
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• 2014

Experimental study has been carried out to understand combustion characteristics of a swirl-stabilized premixed gas turbine combustor for power generation. $NO_x$ and CO emissions, extinction limit, pressure loss, and temperature distribution were measured for various operating conditions. Results show that, with increasing inlet air temperature, $NO_x$ is increased due to a higher adiabatic flame temperature while CO is increased or decreased for low or high A/F ratio regime, respectively. depending on the flame location. With decreasing load from the design condition, $NO_x$ is decreased as thermal load is reduced. With further decreasing load, however, $NO_x$ is increased due to a longer residence time. CO is decreased and then increased with decreasing load. Flame extinction limit is extended with increasing inlet air temperature as the recirculation strength is enhanced.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.6
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• pp.257-266
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• 2015

There is no polynomial-time algorithm that can be obtain the optimal solution for economic load dispatch problem with non-convex fuel cost functions. Therefore, electrical field uses quadratic fuel cost function unavoidably. This paper proposes a valve-point optimization (VPO) algorithm for economic load dispatch problem with non-convex fuel cost functions. This algorithm sets the initial values to maximum powers $P_i{\leftarrow}P_i^{max}$ for each generator. It then reduces the generation power of generator i with an average power cost of $_{max}\bar{c}_i$ to a valve point power $P_{ik}$. The proposed algorithm has been found to perform better than the extant heuristic methods when applied to 13 and 40-generator benchmark data. This paper consequently proves that the optimal solution to economic load dispatch problem with non-convex fuel cost functions converges to the valve-point power of each generator.

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.83-88
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• 2004

As the electric system is getting larger to meet the increasing demand for electric power, the rating of power apparatus is becoming inevitably higher in its working voltage and larger in its capacity. According to KEPCO reports, power transformers in the KEPCO system have undergone troubles such as winding short insulation breakdowns every year since 1981. the cause of this troubles were high one line grounding fault currents in KEPCO systems that had direct grounding systems. KEPCO has installed the NGR(neutral grounding reactor) to lower this fault current and reduced winding short insulation breakdowns in power transformers. But when a circuit breaker opened a no load bus, some trips of circuit breakers for protecting transformer have occurred by mal-operation of 59GT(overvoltage ground relay) that detect disconnection of NGR. Therefore, in this paper, we analyzed the cause and examined the effect of time delav circuit to prevent wrong operation of 59GT.