• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1270-1272
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• 2005

This paper presents a method to reduce the back-emf THD(Total Harmonic Distortion) for the Concentric winding type Interior Permanent Magnet Synchronous Motor(CIPMSM). In the CIPMSM, many design variables and their complicated combinations must be considered to reduce the back-emf THD, but it requires a lot of time and efforts. Therefore, this paper suggests the optimized solution with two simple design parameters using MINITAB software.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.72-77
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• 2015

When connecting 6 lead wires from stator windings to the terminals of 3 phase induction motors for Y or ${\triangle}$ connection, it is feared that the polarities of windings could be reversed each other if the wire tags are lost or erased, resulting in inadmissibly high current to motors in case of starting. To protect motors against such situations, some test procedures are necessary during wire connection which need to be easy ways to electricians without particular tools except a general multi-tester and with less time-consuming in the field. This study focuses on a test measure to satisfy these requirements which is able to provide them a convenient procedure for winding polarity discrimination considering the field condition. Here, the proposed measure utilizes the residual magnetism of the rotor and checks the indication of voltage or current at windings which are induced by the residual flux of rotor when rotating it by hands with 3 stator windings connected in the form of I connection. Principle characteristics and experiment results for this method are analyzed in the view of the effectiveness and applicability for the winding polarity discrimination.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.255-263
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• 2010

The compensated-current-differential relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. Delta winding current is necessary to obtain the modified differential current for a $Y-\Delta$ transformer. This paper describes an estimation algorithm of the delta winding current and its application to a compensated-current-differential relay for a $Y-\Delta$ transformer. Prior to saturation, the core-loss current is calculated and used to modify the differential current. When the core first enters saturation, the initial value of the core flux is obtained by inserting the modified differential current into the magnetization curve. This flux value is used to derive the magnetizing current and consequently the modified differential current. The operating performance of the proposed relay was compared against a conventional current differential relay with harmonic blocking. Test results indicate that the proposed relay remained stable during severe magnetic inrush and over-excitation, and its operating time is significantly faster than a conventional relay. The relay is unaffected by the level of remanent flux and does not require an additional restraining or blocking signal to maintain stability. This paper concludes by implementing the proposed algorithm into a prototype relay based on a digital signal processor.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.341-344
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• 2003

This paper proposes a tree-winding transformer protective relaying algorithm based on the ratio of increment of flux linkages (RIFL). The RIFL of the two windings is equal to the turns ratio for all operating conditions except an internal faults. For a single-phase transformer and three-phase transformer containing the wye-connected windings, the increments of flux linkages are calculated. for a three-phase transformer containing the delta-connected windings, the difference of the increments of flux linkages between the two phases are calculated using the line currents, because the winding currents are practically unavailable. Their ratios are compared with the turns ratio. The results of various tests show that the algorithm successfully discriminates internal faults from normal operation conditions such as magnetic inrush, overexcitation and external faults. The algorithm can not only detect internal winding faults, but reduce the operating time of a relay.

• Journal of Electrical Engineering and Technology
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• v.4 no.3
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• pp.370-376
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• 2009

The influence of magnetic saturation on electromagnetic field distribution in both a permanent-magnet direct-current (PMDC) motor and a field-winding (wound-field) direct-current (FWDC) motor, with the same output mechanical power, has been studied. In this paper, an approximate analytical method and time-stepping Finite Element Method (FEM) are used for prediction of Back-EMF and electromagnetic torque. No-load and rotor-lucked conditions, according to experimental measurements, and the FEM and analytical method studies of the motors have been considered. A sensitivity analysis has also been successfully accomplished on the major design parameters that affect motor performance. At last, these two DC motors are compared, in spite of their differences, on the basis of measured output characteristics.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.229-230
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• 2007

We investigated the quench characteristics of a superconducting element, two superconducting elements in order to increase the current capacity of flux lock type SFCL. The flux-lock type SFCL consisted of the transformer with a primary winding and a secondary winding connected in parallel, and the superconducting element was connected with secondary winding in series. The applied voltage at that time was 160 ${\sqrt{3}}$. We found that the parallel connection between the superconducting elements increased the power capacity and let quench characteristics improve through their mutual linkage.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.11
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• pp.512-515
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• 2003

This paper is to investigate how partial discharge pulse signal can flow in 6.6㎸ motor stator windings. Pulse propagation is experimentally analyzed in stator windings using a variety of frequency-domain techniques. The experiments were performed on two stator windings in the laboratory. Spectrum analyzer(9KHz to 3㎓) with tracking generator(100kHz to 3㎓) was used. Sweep time of the tracking generator was looms. The frequency spectrum of the response signal was detected by active FET probe(1㎓). The active FET probe has a flat amplitude response up to 1㎓ without high frequency attenuation. The stator winding acts as a low-pass filter below 600KHz, the high-frequency components being highly declined. The resonance peaks show about 1.1MHz and 2MHz in low frequency of No. 1 and No. 2 stator windings, respectively. This low-frequency range indicates that attenuation is low. The peaks of partial discharge magnitude show about 900MHz, 1.6MHz in No. 1 stator winding and about 800KHz, 1.4MHz in No. 2 stator winding.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1616-1618
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• 2001

In recent the on-line partial discharge (PD) measurement using sensors, such as EMC, SSC, RTD and RFCT, as an indicator of stator winding insulation condition has been developed. RFCT sensor was placed arounding a grounding lead of surge capacitor to detecting PD. Trend of PD magnitude/phase angle/pulse number over time are useful parameter to diagnosis aging state. We have developed Radio Frequency Current Transformer(RFCT) sensor which is suitable for PD diagnostic measurement in 6.6kV rotating machines. In this paper, we describe the characteristics of RFCT sensor, such as frequency and PD magnitude using 6.6 kV model stator winding in Lab.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.86-88
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• 2004

In this paper, optimal stator slot shape of 3-phase inverter-fed induction motor is designed to reduce stator core and winding losses. For the analysis, the F.E.M on 1 phase band periodic condition in stator is coupled with harmonic equivalent circuit. For the optimal design, the conjugate gradient method is used as an optimizing algorithm. The stator core and winding losses are reduced by the design method. The results are verified by those of the time-step finite element analysis.