• 한국전기전자재료학회논문지
• /
• 제22권12호
• /
• pp.1073-1077
• /
• 2009

The iron core, which comprises the superconducting fault current limiter (SFCL) using magnetic coupling of coils, can be operated in the saturation region, especially at the initial fault period. This operation of the iron core in the saturation region deteriorates the fault current limiting operation of the SFCL. To solve the saturation problem of the SFCL using magnetic coupling of coils, the iron core with two magnetic paths, which has an air-gap in one of them, was adopted. In this paper, the hysteresis characteristics of SFCL using magnetic coupling of coils, which were wound in the iron core with two magnetic paths, were analyzed. Through comparative analysis on the hysteresis characteristics of the iron core comprising SFCL, the hysteresis characteristics of the iron core with two magnetic paths were confirmed to be kept in the non-saturation region during the fault period and thus, the effective fault current limiting operation of the SFCL using the magnetic coupling of coils could be performed.

• Journal of Magnetics
• /
• 제17권4호
• /
• pp.280-284
• /
• 2012

This paper presents a method for evaluating interior permanent magnet synchronous motor (IPMSM) performance over the entire operation region. Using a d-q axis equivalent circuit model consisting of motor parameters such as the permanent magnetic flux, copper resistance, core loss resistance, and d-q axis inductance, a conventional mathematical model of an IPMSM has been developed. It is well understood that in IPMSMs, magnetic operating conditions cause cross saturation and that the iron loss resistance - upon which core losses depend - changes according to the motor speed; for the sake of convenience, however, d-q axis machine models usually neglect the influence of magnetic cross saturation and assume that the iron loss resistance is constant. This paper proposes an analysis method based on considering a magnetic cross saturation and estimating a core loss resistance that changes with the operating conditions and speed. The proposed method is then verified by means of a comparison between the computed and the experimental results.

• 전기학회논문지
• /
• 제56권1호
• /
• pp.66-70
• /
• 2007

For the design to prevent the saturation of the iron core and the effective fault current limitation, the analysis for the operation of the flux-lock type superconducting fault current limiter (SFCL) with consideration for the hysteresis characteristics of the iron core is required. In this paper, the hysteresis characteristics of the flux-lock reactor, which is an essential component of the flux-lock type SFCL, were investigated. Under normal condition, the hysteresis loss of the iron core in the flux-lock type SFCL does not happen due to its winding structure. From the equivalent circuit for the flux-lock type SFCL and the fault current limiting experiments, the hysteresis curves could be drawn. From the analysis for both the hysteresis curves and the fault current limiting characteristics due to the number of turns for the 1st and 2nd windings, the increase of the number of turns in the 2nd winding of the flux-lock type SFCL had a role to prevent the iron core from saturation.

• Transactions on Electrical and Electronic Materials
• /
• 제18권2호
• /
• pp.97-102
• /
• 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.

• 조명전기설비학회논문지
• /
• 제25권2호
• /
• pp.137-142
• /
• 2011

In this paper, the fault current limiting and the hysteresys characteristics of a superconducting fault current limiter (SFCL) using magnetic coupling of two coils on the iron core with an air-gap were analyzed. The introduction of the air-gap in the SFCL with magnetically coupled two coils can suppress the saturation of the iron-core and, on the other hand, make the limiting impedance of the SFCL decreased, which results from the increase of the exciting current. To analyze the effect of the aig-gap on the fault current limiting characteristics of the SFCL, the hysteresys curves of the iron core comprising the SFCL were derived from the short-circuit experiment and the variation in the voltage-current trace of the SFCL during the fault period was analyzed. Through the comparison with the current limiting characteristics of the SFCL without air-gap, the air-gap could be confirmed to contribute to the suppression of the iron core's saturation through the increase of the SFCL's burden from the short-circuit current.

• 대한전기학회논문지
• /
• 제45권4호
• /
• pp.490-500
• /
• 1996

The conventional method to deal with current transformer (CT) Saturation is over dimensioning 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 as some errors may still be present in the secondary current when a severe fault occurs, but also increases the CT size. This paper presents an algorithm for compensating the distorted secondary current of iron-cored CTs under CT saturation using the magnetization (flux-current : .lambda.-i) curve and its performance is examined for fault currents encountered on a typical 345[kV] Korean transmission system, under a variety of different system and fault conditions. In addition, the results of hardware implementation of the algorithm using a TMS320C10 digital signal processor are also presented. The proposed algorithm can improve the sensitivity of relays to low level internal faults, maximize the stability of relays for external faults, and reduce the required CT core cross-section significantly. (author). refs., figs.

• Journal of Power Electronics
• /
• 제10권2호
• /
• pp.176-180
• /
• 2010

This paper deals with a control method to reduce the torque ripple of a permanent magnet synchronous motor (PMSM) for electric power steering (EPS) systems. Such an application requires a very low torque ripple in order to maintain a good steering feel. However, because of spatial limitations, it cannot help having a partial saturation in the iron core of the PMSM for an EPS system, and this saturation results in a significant torque ripple. Thus, this paper analyzes the torque ripple caused by the magnetic saturation of a PMSM and proposes a method with respect to inductance measurement to verify the partial saturation. In addition, it is shown that a compensation current is needed in order to minimize the torque ripple when a PMSM is driven in the high torque region. The estimation process of the current and the torque ripple decreased by the current are presented and verified with test results.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2003년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.89-91
• /
• 2003

For the design to prevent the saturation of iron core and the effective fault current limitation, the analysis for the operation of the flux-lock type superconducting fault current limiter (SFCL) with consideration for the hysteresis characteristics of iron core is required. In this paper, the hysteresis characteristics of flux-lock reactor, which is an essential component of flux-lock type SFCL, was investigated. The hysteresis loss of iron core in flux-lock type SFCL does not happen due to its winding's structure especially in the normal state. From the equivalent circuit for the flux-lock type SFCL and the fault current limiting experiments, the hysteresis curves could be drawn. Through the analysis for both the hysteresis curves and the fault current limiting characteristics due to the number of turns for the 1st and 2nd winding, the increase of the number of turns in the 2nd winding of the flux-lock type SFCL had a role to prevent the iron core from saturation.

• 대한전기학회논문지:전력기술부문A
• /
• 제48권2호
• /
• pp.119-126
• /
• 1999

Current transformer (CT) saturation may cause a variety of protective relays to malfunction. The conventional CT is designed that it can carry up to 20 times the rated current without exceeding 10% ratio error. However, the possibility of CT saturation still remains if the fault current contains substantial amounts of ac and/or dc components. This paper presents a design method of iron-cored CTs for use with protective relays to prevent CT saturation. The proposed design method determines the core cross section of the CT; it employs the transient dimensioning factor to consider relay's operating time (duty cycle) and dc component as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider the biggest fault current. The method designs the cross section of CTs in cases of reclosure and no reclosure.

• Bulletin of the Korean Chemical Society
• /
• 제28권12호
• /
• pp.2279-2282
• /
• 2007

Highly crystalline, uniform Fe nanoparticles were successfully synthesized and encapsulated in zirconia shell using sol-gel process. Two different approaches have been employed for the coating of Fe nanoparticle with zirconia. The thickness of zirconia shell can be readily controlled by altering molar ratio of Fe nanoparticle core to zirconia precursor in the first case where as reaction time was found to be most effective parameter to controlled the shell thickness in the second method. The structure and magnetic properties of the ZrO2-coated Fe nanoparticles were studied. TEM and HRTEM images show a typical core/shell structure in which spherical α-iron crystal sized of ~25 nm is surrounded by amorphous ZrO2 coating layer. TGA study showed an evidence of weight loss of less than 2% over the temperature range of 50-500 °C. The nanoparticles are basically in ferromagnetic state and their magnetic properties depend strongly on annealing temperature. The thermal treatment carried out in as-prepared sample resulted in reduction of coercivity and an increase in saturation magnetization. X-ray diffraction experiments on the samples after annealing at 400-600 °C indicate that the size of the Fe@ZrO2 particles is increased slightly with increasing annealing temperature, indicating the ZrO2 coating layer is effective to interrupt growing of iron particle according to heat treatment.