• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.53 no.7
• /
• pp.382-388
• /
• 2004

The most widely used primary protection for the internal fault detection of power transformers is current percentage differential relaying(PDR). However, the harmonic components could be decreased by magnetizing inrush when there have been changes to the material of iron core or its design methodology. The higher the capacitance of high voltage status and underground distribution, the more differential current includes the second harmonic component during occurrence of an internal fault. Therefore, the conventional harmonic restraint methods need modification. This paper proposes an advanced protective relaying algorithm by fluxt-differential current slope characteristic and trend of voltage and differential current. To evaluate the performance of proposed algorithm, we have made comparative studies of PDR fuzzy relaying, and DWT relaying. The paper is constructed power system model including power transformer, utilizing the WatATP99, and data collection is made through simulation of various internal faults and inrush. As the results of test. the new proposed algorithm was proven to be faster and more reliable.

• Proceedings of the KIEE Conference
• /
• 2002.11b
• /
• pp.274-276
• /
• 2002

This paper proposes a current differential relaying algorithm for power transformers using the third difference function of a differential current. The algorithm observes the instants when the wave-shape of the differential current is changed due to the change of the magnetization inductance. If the value of the third difference is bigger than the threshold, the output of a current differential relay is blocked for a cycle. In the cases of magnetic inrush and overexcitation, the blocking signal is maintained: however, for internal faults, reset in a cycle. The test results clearly show that the algorithm successfully distinguishes internal faults from magnetizing inrush.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.8 no.5
• /
• pp.72-82
• /
• 1998

Power transformer protective relay should block the tripping during magnetizing imrush and rapidly operate the tripping during internal faults. But traditional approaches maloperate in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmounic component. To enhance the fault detection sensitivities of conventional technuques, flux-differential current derivative curve by fuzzy theory approaches is used. This paper deals with fuzzy logic based protective relaying for power transformer. The proposed fuzzy based relaying algorithm consisits of flux-differential current derivative curve, harmonics restraint, and precentage differential characteristic curv. The proposed relaying was tested with relaying signals obtained from Salford EMTP simulation package and showed a fast and accurate trip operation.

• Proceedings of the KIEE Conference
• /
• 2003.07a
• /
• pp.320-322
• /
• 2003

This paper describes a current differential relaying algorithm for a three-phase transformer considering the nonlinear magnetization characteristics of the core. The iron-loss current is obtained from the calculated induced voltage and the core-loss resistance. The magnetizing current is calculated from the estimated core flux and the magnetization curve. The proposed algorithm uses the modified differential current, which is obtained by subtracting the iron-loss current and the magnetizing current from the conventional differential current. The various test results show that the algorithm can discriminate internal fault from magnetic inrush, overexcitation and an external fault.

• Proceedings of the KIEE Conference
• /
• 2004.07e
• /
• pp.92-95
• /
• 2004

Power transformer is an important apparatus in transforming and delivering the power in a power system. It shows less accident ratio than other system apparatus, but once the accident occurs, it causes long-term operation stoppage and economic loss. It brings high bad spillover effects. Therefore, the role of protective relaying, which is to prevent internal fault a power transformer is highly important. This study proposed advanced algorithm that can clearly determine internal fault of the power transformer and magnetizing inrush, through numerical analysis by using the terminal voltage and input output current.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.55 no.3
• /
• pp.95-101
• /
• 2006

This paper proposes a modified current differential relay for $Y-{\Delta}$ transformer protection. The 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. A method to estimate the circulating component of the delta winding current is proposed. To cope with the remanent flux, before saturation, the core-loss current is calculated and used to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Test results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation, because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay does not require additional restraining signal and thus cause time delay of the relay.

• Proceedings of the KIEE Conference
• /
• 2002.07a
• /
• pp.16-18
• /
• 2002

This paper proposes a difference-blocked current differential relaying algorithm for power transformers. The proposed algorithm observes that the shape of the differential current is changed using the difference. If the change is detected, output of current differential relay is blocked for a certain time. In this way, the algorithm distinguishes internal faults from magnetizing inrush. The proposed algorithm uses only currents and is unaffected by the remanent flux.

• Proceedings of the KIEE Conference
• /
• 2003.07a
• /
• pp.268-270
• /
• 2003

This paper proposes a software design and hardware implementation of Intelligent Electronic Device(IED) for power transformer. The relaying algorithm is based on DFT. The protection functions implemented include RDR with a second harmonic restraint for magnetizing inrush, OCR, OCGR, OVR, and UVR etc. The main board of IED is based on the TMS32C32 Processor. The IED was tested with relaying signals obtained for EMTP simulation package.

• Proceedings of the KIEE Conference
• /
• 2003.11a
• /
• pp.210-212
• /
• 2003

Conventional PDC relaying with 2nd harmonic restraint makes some doubt in reliability. It can contain second harmonic component to a large extent even during internal fault, and shows a tendency of relative reduction because of the advancement of transformer's core material. It is, therefore, necessary to develop a new algorithm as well as a new technique for the effective and accurate discrimination. This paper deals with advanced algorithm, fuzzy logic based relaying by using flux differential, and a new fault detection criterion logic scheme by using wavelet transform. To comparative analysis of proposed techniques, the paper constructs power system model including power transformer, utilizing the EMTP, and collects data through simulation of various internal faults and magnetizing inrush.

• Proceedings of the KIEE Conference
• /
• 2004.11b
• /
• pp.217-219
• /
• 2004

The second harmonic component could be decreased by magnetizing inrush when there have been changes to the material of the iron core or its design methodology. The higher the capacitance of the high voltage status and underground distribution, the more the differential current includes the second harmonic during the occurrence of an internal fault. Therefore, the conventional second harmonic-restrained RDR needs modification. This paper describes an advanced numerical algorithm that utilizes terminal voltage, differential current harmonics, harmonic ratio, and flux-differential current slope. Based on the results of testing with WatATP99 simulation data, the proposed algorithm was proven to be faster and more reliable.