• 한국초전도ㆍ저온공학회논문지
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• 제21권4호
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• pp.39-43
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• 2019

The breaking of a circuit in DC grid could pose a challenge because of the absence of zero-crossing instant for both current and voltage when a fault occurs. An additional fault current limiting function will be very helpful for reducing the burden of the DC circuit breaker by limiting the fault current to a reasonable value. In this paper, we studied the overcurrent characteristics of several HTS conductors so that we could use the selected conductors for the basic design work of a resistive type fault current limiting module as a part of the circuit breaking system. According to the short-circuit test results, we suggested and compared two different basic design parameters of the HTS fault current limiting module, which will be connected in series to the DC circuit breaker.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 C
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• pp.1363-1365
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• 1999

This paper Presents an algorithm for the computation of fault location for a transmission line by means of the voltage and current signals. It is impossible to calculate the accurate fault distance, because of the fault resistance and fault current which are unknown. All Currents in the lines are divided by the current distribution factor, so the fault current through the fault resistance can be represented by using data from one terminal of transmission line. This algorithm proposed can calculate the fault distance with only the faulty phase information.

• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.474-483
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• 2011

Solid-state fault current limiters (SSFCL) in power systems are alternative devices to limit prospective short circuit currents from reaching lower levels. Fault current limiters (FCL) can be classified into two categories: R-type (resistive) FCLs and L-type (inductive) FCLs. L-type FCL uses an inductor to limit fault level and is more efficient in suppressing voltage drop during a fault. In contrast, R-type FCL is constructed with a resistance and is more effective in consuming the acceleration energy of generators during a fault. Both functions enhance the transient stability of the power system. In the present paper, a novel SSFCL is proposed to enhance power system transient stability and power quality. The proposed SSFCL uses both functions of an L-type and R-type FCL. SSFCL consists of four diodes, one self-turn-off IGCT, a current-limiting by-pass inductor (L), and a variable resistance parallel with an inductor for improvement of power system stability and prevention of over-voltage across SSFCL. The main advantages of the proposed SSFCL are the simplicity of its structure and control, low steady-state impedance, fast response, and the existence of R-type and Ltype impedances during the fault, all of which improve power system stability and power quality. Simulations are accomplished in PSCAD/EMTDC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.148-150
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• 2002

Recently the demand for electrical power is significantly increased due to the life improvement of customers. Correspond to the result, the transmission capacity is larger, also the fault current is significantly larger. Within the methods of limiting this fault current, the methods of using the fault current limiter is on the rise. If the Superconducting Fault Current Limiter(SFCL) is applied, then the power delivery loss doesn't exist between the plural power systems, also the fault current can be reduce. But for applying the real system, it needs to investigate the effect of SFCL before appling to real power systems. Consequently, the fault of transmission with SFCL was simulated using EMTP. It was investigated to the effect of SFCL at the 345[kV] transmission fault according to compare with the case of appling SFCL and removing SFCL.

• 제어로봇시스템학회논문지
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• 제20권6호
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• pp.635-640
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• 2014

Detection and diagnosis of incipient bearing fault in an induction motor is important for the prevention of serious motor failure. This paper presents an analysis of the effect of a faulty bearing on the stator current of an induction motor. A bearing fault leads to torque oscillations which result in phase modulation of the stator current. Since the torque oscillations cause specific frequency components at the stator current spectrum to rise sharply, the bearing fault can be detected by checking out the faultrelated frequency. In this paper, a mathematical model of the load torque oscillation caused by a bearing fault is presented. The proposed model can be used to analyze the physical phenomenon of a bearing fault in an induction motor. In order to represent the bearing fault effect, the proposed model is combined with an existing model of vector-controlled induction motors. A set of simulation results demonstrate the effectiveness of the proposed model and represent that bearing fault detection using a stator current is useful for vector-controlled induction motors.

• 전기학회논문지
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• 제65권5호
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• pp.873-877
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• 2016

This paper proposed the structure that applied superconductors to the neutral line of a transformer and applied the normal conductors to the third line. The superconductor applied to the neutral line of a transformer limited the peak value of initial fault current, while the normal conductor finally limited the fault current. In order to secure the operating reliability of transformer type Superconducting Fault Current Limiter (SFCL) of previously proposed structure, we analyzed the operating characteristics according to the fault types. We tested a line-to-ground fault and a line-to-line fault. As a result of the experiment, all the faults showed that the superconductor stably limited the peak-value of initial fault current. Also, the normal conductor finally limited the fault current. Based on this research results, We thought that if the structure of inserting superconductor into the neutral line is applied to the real system, it could improve the reliability and stability of the power system.

• 대한전기학회논문지:전력기술부문A
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• 제52권2호
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• pp.121-133
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• 2003

This paper presents a fault location algorithm for a single phase-to-ground fault on 3-terminal transmission systems. The method uses only the local end voltage and current signals. Other currents used for the algorithm are estimated by current distribution factors and the local end current. Negative sequence current is used to remove the effect of load current. Five distance equations based on Kirchhoff's voltage law are established for the location algorithm which can be applied to a parallel transmission line having a teed circuit. Separating the real and imaginary parts of each distance equation, final nonlinear equations that are functions of the fault location can be obtained. The Newton-Raphson method is then applied to calculate the estimated fault location. Among the solutions, a correct fault distance is selected by the conditions of the existence of solution. With the results of extensive S/W and H/W simulation tests, it was verified that the proposed algorithm can estimate an accurate fault distance in a 154kV model system.

• 한국초전도ㆍ저온공학회논문지
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• 제16권2호
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• pp.59-63
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• 2014

HTS power cable bypass the fault current through the former to protect superconducting tapes. On the other hand, the fault current limiting (FCL) power cable can be considered to mitigate the fault current using its increased inductance and resistance. Using the increased resistance of the cable is similar to the conventional resistive fault current limiter. In case of HTS power cable, the magnetic field of HTS power cable is mostly shielded by the induced current on the shield layer during normal operation. However, quench occurs at the shield layer and its current is kept below its critical current at the fault condition. Consequently, the magnetic field starts to spread out and it generates additional inductive impedance of the cable. The inductive impedance can be enhanced more by installing materials of high magnetic susceptibility around the HTS power cable. It is a concept of SFCL power cable. In this paper, a sample SFCL power cable is suggested and experimental results are presented to investigate the effect of iron cover on the impedance generation. The tests results are analyzed to verify the generation of the inductive and resistive impedance. The analysis results suggest the possible applications of the SFCL power cable to reduce the fault current in a real grid.

• 한국전기전자재료학회논문지
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• 제23권2호
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• pp.159-163
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• 2010

The superconducting fault current limiter (SFCL) plays a role in compensating the voltage sag of the sound feeder adjacent to the fault feeder as well as the fault current limiting operation of the fault feeder. Especially, the SFCL using magnetic coupling of two coils with parallel connection has different voltage sag compensating and current limiting characteristics due to the winding direction and the inductance ratio of two coils. In this paper, the current limiting and the voltage sag compensating characteristics of a SFCL using magnetic coupling of parallel connected two coils were analyzed. Through the analysis on the experimental results considering the winding direction of two coils, the SFCL designed with the additive polarity winding was shown to have the higher limited fault current than the SFCL designed with the subtractive polarity winding. In addition, it could be confirmed that the higher fault current limitation of the SFCL could be contributed to the higher load voltage sag compensation.

• 한국초전도ㆍ저온공학회논문지
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• 제9권1호
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• pp.37-42
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• 2007

We are developing a 22.9 kV/25 MVA superconducting fault current limiting(SFCL) system for a power distribution network. A Bi-2212 bulk SFCL element, which has the merits of large current capacity and high allowable electric field during fault of the power network, was selected as a candidate for our SFCL system. In this work, we experimentally investigated important characteristics of the 190 kVA Bi-2212 SFCL element in its application to the power grid e.g. DC voltage-current characteristic, AC loss, current limiting characteristic during fault, and so on. Some experimental data related to thermal and electromagnetic behaviors were also compared with the calculated ones based on numerical method. The results show that the total AC loss at rated current of the 22.9 kV/25 MVA SFCL system, consisting of one hundred thirty five 190 kVA SFCL elements, becomes likely 763 W, which is excessively large for commercialization. Numerically calculated temperature of the SFCL element in some sections is in good agreement with the measured one during fault. Local temperature distribution in the190 kVA SFCL element is greatly influenced by non-uniform critical current along the Bi-2212 bulk SFCL element, even if its non-uniformity becomes a few percentages.