• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
• /
• pp.299-302
• /
• 2002

The second harmonic component is commonly used for blocking differential relay in Power transformers. However it is difficult to distinguish between inrush and internal winding fault with differential current protective relaying. This paper proposed a new method using nuro-fuzzy. The used data in nuro-fuzzy algorithm are 3-phase primary voltage and fundamental harmonic of differential current. Various states of transformer are simulated using BCTRAN and HYSDAT of EMTP. As a result of applying the algorithm in various cases, the correct discrimination between internal winding fault and inrush performed.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2003년도 하계학술대회 논문집 A
• /
• pp.552-554
• /
• 2003

The second harmonic component is commonly used for blocking differential relay in power transformers. However, it is difficult to distinguish between inrush and internal winding fault with differential current protective relaying. This paper proposed a new method using Nuro-Fuzzy System based on HCM(Hard C-Means). The proposed system is more objective and systematic than existing model. The data used in input are 3-phase primary voltage and fundamental harmonic of differential current. Various states of transformer are simulated using BCTRAN and HYSDAT of EMTP. As a result of the application of algorithm in various cases, the exact discrimination between internal winding fault and inrush is performed.

• 대한전기학회논문지:전력기술부문A
• /
• 제54권5호
• /
• pp.242-250
• /
• 2005

This paper proposes a new protective relaying algorithm using Neuro-Fuzzy and wavelet transform. To organize advanced nuero-fuzzy algorithm, it is important to select target data reflecting various transformer transient states. These data are made of changing-rates of Dl coefficient and RSM value within half cycle after fault occurrence. Subsequently, advanced neuro-fuzzy algorithm is obtained by converging the target data. As a result of applying the advanced neuro-fuzzy algorithm, discrimination between internal fault and inrush is correctly distinguished within 1/2 after fault occurrence. Accordingly, it is evaluated that the proposed algorithm can effectively protect a transformer by correcting discrimination between winding fault and inrushing state.

• Journal of Electrical Engineering and Technology
• /
• 제5권2호
• /
• pp.255-263
• /
• 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.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1996년도 하계학술대회 논문집 B
• /
• pp.671-673
• /
• 1996

Simulation methods using EMTP to analyze power transformer transient characteristics and their interesting results are presented in this paper. Because of the transformer saturation including initial inrush, the conventional current differential relay with harmonic restraint module does not provide a clear distinction between internal faults and other conditions. Providing the bases to develop a new relaying concept for power transformer protection, transformer nonlinear transient characteristics are analyzed.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 B
• /
• pp.744-746
• /
• 2002

In this paper the method to limit inrush currents for unloaded transformers is proposed by controlling the opening instant in order to predetermine the residual flux. For the purpose of verifying the performance of the proposed method the test circuit with a single phase transformer is established and the effect of the controlled method is studied. With the basis of the obtained results the controlled method for three phase transformers with a wye-delta winding is also proposed. The analysis studies using EMTP(Electro-Magnetic Transient Program) are carried out in order to reveal its effectiveness.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2001년도 하계학술대회 논문집 A
• /
• pp.35-37
• /
• 2001

The four fuzzy criteria to distinguish the internal fault from the inrush for the power transformer protection have been identified. They are based on the wave shape, terminal voltage, fundamental and second harmonic component of differential current. A systemetic way to determine the associated fuzzy membership function is also proposed.

• 산업기술연구
• /
• 제14권
• /
• pp.89-100
• /
• 1994

The effects of transient inrush currents on the dynamic characteristics of percentage differential relays are studied when the power transformers are reenergized. An algorithm of estimation the nonlinear magnetic property of power transformer and current trnasformer core are developed. Using this method, we can analyze the effect of inrush currents on the trip region of the percentage differential relays corresponding to the variation of the phase angle and the residual magnetism at the instant of switch closing. Test results are used to verify the availibility of the proposed algorithm. Finally a case study is performed to the 110 MVA main transformer in hydraulic power station.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.559-560
• /
• 2007

In the case of the transformers including the delta winding such as a three-phase Y-Y-$\Delta$ transformer, a delta winding current flows in the delta windings. The delta winding current of a three-phase Y-Y-$\Delta$ transformer is decomposed into a non-circulating current and a circulating current. The former can be estimated directly from the line currents, but the latter can not. This paper proposes an estimation method for a circulating current of a Y-Y-$\Delta$ Transformer. A first order differential equation for the circulating current is derived by applying the Kirchhoff's voltage law on the loop of the delta side. The circulating current can be estimated by solving the differential equation. Various test results indicate the algorithm can estimate the circulating current accurately even under over-excitation and magnetic inrush.

• 전기학회논문지
• /
• 제56권11호
• /
• pp.1873-1878
• /
• 2007

Current differential relays may maloperate during magnetic inrush and over-excitation because a significant differential current is produced. To prevent maloperation, the relays adopt some harmonic components included in the differential current. The harmonic restraints may increase the security of a relay but cause the operating time delay of a relay when an internal fault occurs. Moreover, the operating time delay is more increased if a current transformer (CT) is saturated. This paper describes a current differential relaying algorithm for power transformer protection with a compensating algorithm for the secondary current of a CT. The comparative study was conducted with and without the compensating algorithm. The performance of the proposed algorithm was investigated when the measurement CT (C400) and the protection CT (C400) are used. The proposed algorithm can compensate the distorted current of a CT and thus reduce the operating time delay of the relay significantly for an internal fault with CT saturation.