• Journal of Electrical Engineering and Technology
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• 제2권1호
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• pp.35-41
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• 2007

This paper presents the results of investigating harmonic levels on medium voltage motors at loading conditions in air separation plant. The essential results of the measurements of the medium voltage motor harmonics are summarized in the values for the total harmonic distortion (THD). Motors loading case is used to assess the current and voltage harmonic distortions. Proper system analysis is important when adding a new motor starting and controlling the equipment. With the result of the paper it is possible to suggest the most appropriate starting and control method. Two medium voltage motors of air separation unit measurement results and simulations are summarized. Both current and voltage harmonic distortions are fitted by using a linear and exponential regression model. The prediction of THD values can be used for this kind of process for future planning by utilities.

• 전기학회논문지
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• 제58권12호
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• pp.2453-2461
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• 2009

Faults caused by medium-voltage customers have been increased and enlarged their portion in total distribution faults even though we have done many efforts. In the previous paper, we suggested the fault prediction model and fault prevention method for these distribution line faults. However we can't directly apply this prediction model in the field. Because we don't have an useful program to predict those customers causing distribution line faults. This paper presents the construction method of data warehouse in ERP system and the program to find customers who cause distribution line faults in medium-voltage customer's electric facility management applying data mining techniques. We expect that this data warehouse and prediction program can effectively reduce faults resulted from medium-voltage customer facility.

• 전기학회논문지
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• 제58권10호
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• pp.1869-1880
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• 2009

Distribution line fault has been reduced gradually by the efforts on improving the quality of electrical materials and distribution system maintenance. However faults caused by medium voltage customers have been increased gradually even though we have done many efforts. The problem is that we don't know which customer will cause the fault. This paper presents the concept to find these customers using data mining techniques, which is based on accumulated fault records of medium voltage customers in the past. It also suggests the prediction model construction of medium voltage customers causing distribution line fault and methods to enhance the reliability of distribution system. We expect that we can effectively reduce faults resulted from medium voltage customers, which is 30% of total faults.

• 전력전자학회논문지
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• 제22권4호
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• pp.285-296
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• 2017

This paper proposes an improved modulation scheme for the medium voltage modular multi-level converter (MMC), which operates in the nearest level control and applies in the medium voltage direct current (MVDC) system. In the proposed modulation scheme, the offset (neutral-to-zero output) voltage is adjusted, with the phase voltage magnitude, thereby maintaining a constant value with N+1 level in the controllable modulation index (MI) range. In order to confirm the proposed scheme's validity, computer simulations for the 22.9 kV - 25 MVA MMC were performed with PSCAD/EMTDC, as well as hardware experiments for the 380 V - 10 kVA MMC. The proposed modulation scheme offers to build a constant pole voltage regardless of the MI value, and to build a phase voltage with improved total harmonic distortion (THD).

• Journal of Power Electronics
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• 제10권2호
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• pp.155-164
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• 2010

This paper presents a voltage control algorithm for a hybrid multilevel inverter based on a staged-perception of the inverter voltage vector diagram. The algorithm is applied to control a three-stage eighteen-level hybrid inverter, which has been designed with a maximum number of symmetrical levels. The inverter has a two-level main stage built using a conventional six-switch inverter and medium- and low- voltage three-level stages constructed using cascaded H-bridge cells. The distinctive feature of the proposed algorithm is its ability to avoid the undesirable high switching frequency for high- and medium- voltage stages despite the fact that the inverter's dc sources voltages are selected to maximize the number of levels by state redundancy elimination. The high- and medium- voltage stages switching algorithms have been developed to assure fundamental switching frequency operation of the high voltage stage and not more than few times this frequency for the medium voltage stage. The low voltage stage is controlled using a SVPWM to achieve the reference voltage vector exactly and to set the order of the dominant harmonics. The inverter has been constructed and the control algorithm has been implemented. Test results show that the proposed algorithm achieves the desired features and all of the major hypotheses have been verified.

• 한국전기전자재료학회논문지
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• 제18권8호
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• pp.685-689
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• 2005

In the fabrication and design of MLCCs (Multilayer Ceramic Capacitors) with Ni inner electrode for medium and high voltage, reliability and dielectric breakdown mode have been investigated. For thickness of green sheet, the relationship between the rated voltage versus the thickness of green sheet. Increasing the thickness of green sheet increases the dielectric breakdown voltage. However, a practical limit to this linear relationship occurs at 30 urn and above. As the thickness of green sheet increased, dielectric breakdown voltage and weibull coefficient is increased, but abruptly decrease at 30 urn and 36 urn. When 24 urn of green sheet thickness, weibull coefficient and dielectric breakdown voltage were 13.58 and 70 V/um respectively. The results enabling the MLCCs to demonstrate high levels of reliability at medium and high voltage.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 D
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• pp.3040-3042
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• 2005

During the last several years, interest in broad-band power line communications (PLC) has been grown over medium voltage(MV) power distribution lines as well as low voltage lines. This paper introduces a medium voltage PLC test field that is set up in the suburbs of Euiwang city in Korea. This test field could be used not only for the measurement of communication channel environment but also for internet service. This paper shows the configuration of medium voltage test field with network devices like MV signal coupler and the results of channel environment like noise and impulse response. It also shows the service performance of PLC access network through network management system.

• Journal of Power Electronics
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• 제16권6호
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• pp.2076-2084
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• 2016

In this paper, a novel scheme to eliminate common-mode voltage (CMV) is proposed for three-level neutral-point clamped (NPC) inverters. In the proposed scheme, a low-power full-bridge converter is utilized to produce compensatory voltage for CMV, which is injected into an NPC inverter through a single-phase four-winding transformer. With the proposed circuit, the power range for applications is not limited, and the maximum modulation index of the inverter is not reduced. These features are suitable for high-power medium-voltage machine drives. The effectiveness of the proposed method is verified by simulation and experimental results.

• 한국통신학회논문지
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• 제30권12A호
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• pp.1136-1146
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• 2005

본 논문에서는 전력선 통신을 위해 사용되는 고압 배전선로에서 통신신호 및 잡음신호에 의해 방사되는 방사전계강도를 계산하였다. 전력선 통신 네트워크의 2포트 등가모델 및 기본적인 전송선로 이론을 이용해 입력임피던스를 계산하였다. 그리고 계산된 입력임피던스를 이용해 전력선상 전류를 계산하고 최종적으로 방사전계강도를 계산하였다. 전력선의 특성임피던스가 매우커서 입력 단에서의 반사가 심하기 때문에 입력임피던스는 일정한 주기를 가지는 정재파 형태를 가진다. 계산된 전류 및 방사전계 또한 이러한 형태임을 알 수 있었다. 실제 측정한 결과계산 치와 측정치가 매우 유사함을 알 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1369-1374
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• 2014

Most accidents of medium-voltage cables installed in nuclear power plants result from the initial defect of internal insulators or the initial failure due to poor construction. However, as the service years of plants increase, the possibility of cable accidents is also rapidly increases. This is primarily caused by electric, mechanical, thermal, and radiation stresses. Recently, much attention is paid to the study of cable diagnoses. To date, partial discharge and Tan${\delta}$ measurements are known as reliable methods to diagnose the aging of medium-voltage cables. High frequency partial discharge measurement techniques have been widely used to diagnose cables in transmission and distribution systems. However, the on-line high frequency partial discharge technique has not been used in the nuclear power plants because of the plant shutdown risk, degraded measurement sensitivity, and application problems. In this paper, the partial discharge measurement with a portable device was tried to evaluate the integrity of the 4.16kV and 13.8kV cable lines. The test results show that the high detection sensitivity can be achieved by the high frequency partial discharge technique. The present technique is highly attractive to diagnose medium voltage cables in nuclear power plants.