• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.4
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• pp.214-220
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• 2004

This paper describes a busbar current differential relay in conjunction with a current transformer(CT) compensating algorithm irrespective of the level of the remanent flux. The compensating algorithm detects the start of first saturation if the third-difference function of the current exceeds the threshold; it estimates the core flux at the first saturation start by inserting the negative value of the third-difference function of the current into the magnetization curve; thereafter, it calculates the core flux during the fault and compensates the distorted current using the magnetization curve. The algorithm estimates the correct secondary current irrespective of the level of the remanent flux and needs no saturation point of the magnetization curve. The proposed relay can improve not only security of the relay on an external fault with CT saturation but sensitivity of the relay on an internal fault; the relay can improve the operating speed on n internal fault with CT saturation. This paper concludes by implementing the relay into a digital signal processor based prototype relay.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.4
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• pp.214-214
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• 2004

This paper describes a busbar current differential relay in conjunction with a current transformer(CT) compensating algorithm irrespective of the level of the remanent flux. The compensating algorithm detects the start of first saturation if the third-difference function of the current exceeds the threshold; it estimates the core flux at the first saturation start by inserting the negative value of the third-difference function of the current into the magnetization curve; thereafter, it calculates the core flux during the fault and compensates the distorted current using the magnetization curve. The algorithm estimates the correct secondary current irrespective of the level of the remanent flux and needs no saturation point of the magnetization curve. The proposed relay can improve not only security of the relay on an external fault with CT saturation but sensitivity of the relay on an internal fault; the relay can improve the operating speed on n internal fault with CT saturation. This paper concludes by implementing the relay into a digital signal processor based prototype relay.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1407-1409
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• 1999

Distance relay is being used for transmission line protection. Recently, current differential relay is used with high reliability in power system. This kind of relay is reported that it has a reliable detection ability, even so high impedance faults take place in transmission line. Therefore it is expected to use and expand widely in many utilities. Tripping of the relay is decided according to the difference between differential and restraint current. However the tripping criterion can be changed by the manufacturers. This paper presents an operational scheme of current differential relay for transmission line protection with graphical model. It is developed for educational purpose for students interesting in power system and protection engineer in utility. MATLAB is used to establish the models.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.6
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• pp.671-676
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• 2015

Cooperative networks eliminate shadow area using relay and enhance communication performance by creating virtual multi input multi output (MIMO) system. In this paper, we analyze the performance of cooperative networks which use coherent modulation scheme in source-relay nodes and differential modulation scheme in relay-destination nodes depending on the relay location. We consider the performance analysis of systems with and without the direct transmission between source and destination node where the direct transmission adopts differential modulation scheme. In addition, the performance of the system with fully differential modulation scheme is compared with the system using partially differential modulation scheme. The performance of system is based on the symbol error rate between source and destination node.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.329-331
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• 2003

PROSET2000 that is integrated protective management system had developed and used in order to automate the setting process of protective relays in transmission system protection. PROSET2000 have database for relay setting and automated for relay setting program within. This paper proposed PCM current differential relay setting program point of Object Oriented Programming paradigm using Unified Modeling Language about additional relay in PROSET2000. Nevertheless each relay uses same current differential but setting method is different. This paper discribed different thing about setting method of each relay and evaluated more effective and corrective relay setting program using UML.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.262-265
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• 2003

During magnetic inrush or over-excitation saturation of the core in a transformer draws a large exciting current. This can cause mal-operation of a differential relay. This paper proposes a modified current differential relay for transformer protection. In order to cope with the remanent flux at the beginning. the start of saturation of the core is detected and the core flux at the instant is estimated by inserting the differential current into a magnetization curve. Then, this core flux value can be used to calculate the core flux. The proposed relay calculates the core-loss current from the induced voltage and the core-loss resistance; the relay calculates the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss current and the magnetizing current from the conventional differential current. The proposed technique not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the speed of the conventional relay.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1801-1806
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• 2012

This paper presents a simple and practical method which enables to prevent malfunction of protection relay due to differential current caused by one end CT saturation in case of external fault. This method uses difference of magnitude(instantaneous value) between the both end current just before the occurrence of differential current without a separate method to CT staturation detection. One end CT saturation is simulated by current transformer model using type-96 component and the presented method is verified by using EMTP MODELS with respect to internal and external fault with one end CT staturation. The presented method distinguished rightly bewteen external and internal fault with one end CT saturation. This information can be used to prevent malfunction of current differential protection relay in case of external fault. And this method is not affected by sampling rate and has no calculation burden, so it will be applicable to differential current protection relay with ease.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.8-13
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• 2011

A percentage current differential relay is widely used for transformer protection. Because many percentage current differential relays recently use modified methods instead of conventional methods for deciding the operating characteristics of the large current region, in this paper, the operating region of a percentage current differential relay is analyzed in input-output current domain instead of operating-restraint current domain. An effective method to set the operating region when a CT is saturated is proposed with a series of investigations comparing a conventional method with the proposed modified method. The performance of the proposed method is evaluated for internal and external faults of a power transformer having the voltage rating of 345/154kV. EMTP-RV is used for the relaying data collection.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.3
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• pp.226-233
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• 1999

Protective relay for transformer operates in general by comparing with the differential current and the restraint current. These kinds of currents are changed on magnitude and phasor during the fault according to winding type and vector group. This paper presents the differential and restraint currents and operational principle of differential protective relay for two-winding and three-winding transformer with graphical mode. It is developed using MATLAB for and educational purpose on engineer related in power system and protection in university and power utility including large factory.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.6
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• pp.99-105
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• 2014

Power transformers are applied throughout the power system to connect systems of different voltage to one another. Since a ratio differential relay offers high sensitivity in detection of internal faults in power transformers, it is widely used in the main protection system. The use of nonlinear devices such as rectifiers and other devices utilizing solid state switching have been increased in industry during recent years. For nonlinear loads, the load current is not proportional to the instantaneous voltage. This situation creates harmonic distortion on the system. The harmonic could differential relay misoperation if not recognized. This paper aims at analyzing and probing into the influences of harmonics on a ratio differential relay for power transformer protection.