Magnetic Inrush Research Articles

Materials and Cutting Method Effects of Three Phase Transformer-Core on Magnetization Curve and Inrush Current: Simulation Approach

This paper dealt with simulation approach of the effect of type of material and cutting method of three phases transformer core on magnetization curve as well as inrush current. Different to the one of single phase transformer, flux density affected magnetization curve as well inrush current are change every cycle of three phases sources even in a same point investigated. In fact it is much more complex compared to a single phase transformer. Three kinds of material and two cutting methods were investigated in order to understand how it affect the magnetization curve as well as it inrush current. Investigation done is emphasized on simulation based on finite element method. A simple mathematical approach is also done to obtain the peak value of inrush current. The result showed that material and cutting method affect the magnetization curve and inrush current significantly. The generated inrush current in different cutting method has the difference about 6.8% while ST-37 material has the largest generated inrush current of about 9 times compared to ST-1008 and 4 times compared to ST-1010 material.

Wavelet Transforms Based Power Transformer Protection from Magnetic Inrush Current

The Power transformer is the very essential element in the power systems. For wealthy running operation of power transmission and distribution, the transformer set-up is indispensable. Otherwise, under fault situation the whole transmission system will lead to power loss. The protection is necessary for power transformers i.e. mostly against internal faults and magnetic inrush currents. Exciting magnetic inrush current will tide, when the transformer is operated without keeping load or in the Voltage recovery after the fault being separated. This work suggests to develop transient detection techniques using wavelet transform for all these faults. The wavelet transform has a benefit of representation of current and Voltage signals. Empathy of transients is very fast and precise the research proposes to expand a new wavelet method to identify inrush currents to classify it from power system disturbances. The suggested practice extract faults and inrush generated transient signals using wavelet transform process. DOI: http://dx.doi.org/10.11591/telkomnika.v14i3.7849

Discrimination of internal fault from magnetising inrush current in power transformers based on sine‐wave least‐squares curve fitting method

This study deals with a method for discrimination between magnetising inrush and internal fault currents in three-phase transformers based on sine-wave curve fitting. A sine wave is fitted to the normalised differential current by using the least-squares technique for each phase. The difference between the normalised differential currents and the fitted signals are calculated, which are hereafter named residual signals (RSs). Maximum range of the RSs variations is utilised for the definition of a simple criterion. Based on this criterion, the discrimination is realised within less than a half cycle of power frequency. In order to eliminate the impact of the current transformer (CT) saturation on the performance of the proposed technique, the currents are compensated by a CT saturation compensation algorithm in the first step. The proposed method is evaluated and compared with some well-known methods by a large number of simulation and experimental data. Furthermore, the proposed algorithm is evaluated in the case of a transformer, which is fed through a feeder with series capacitors. The results confirm that reliability, accuracy and speed response of the proposed technique is more than the other methods.

Characteristic Analysis of Ship Transformer Magnetizing Inrush Current and its Suppression Method

Medium voltage in the electric power system of ship typically is powered by a large capacity transformer for low voltage electrical apparatus. When switching on, the primary side of transformer will produce very large current, which would endanger the safe operation of power for ships. The mechanism and characteristics of magnetizing inrush current is analyzed when the transformer switches with no load. We think that the reason caused magnetizing inrush current is transformers saturation. Pre-excitation is presented through a small volume transformer magnetizing method of suppressing the inrush current of transformer and validated by simulation and experiment.

Induced Voltages Ratio-Based Algorithm for Fault Detection, and Faulted Phase and Winding Identification of a Three-Winding Power Transformer

This paper proposes an algorithm for fault detection, faulted phase and winding identification of a three-winding power transformer based on the induced voltages in the electrical power system. The ratio of the induced voltages of the primary-secondary, primary-tertiary and secondary-tertiary windings is the same as the corresponding turns ratio during normal operating conditions, magnetic inrush, and over-excitation. It differs from the turns ratio during an internal fault. For a single phase and a three-phase power transformer with wye-connected windings, the induced voltages of each pair of windings are estimated. For a three-phase power transformer with delta-connected windings, the induced voltage differences are estimated to use the line currents, because the delta winding currents are practically unavailable. Six detectors are suggested for fault detection. An additional three detectors and a rule for faulted phase and winding identification are presented as well. The proposed algorithm can not only detect an internal fault, but also identify the faulted phase and winding of a three-winding power transformer. The various test results with Electromagnetic Transients Program (EMTP)-generated data show that the proposed algorithm successfully discriminates internal faults from normal operating conditions including magnetic inrush and over-excitation. This paper concludes by implementing the algorithm into a prototype relay based on a digital signal processor.

Saturation Detection-Based Blocking Scheme for Transformer Differential Protection

This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second- and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay.

Research on the Influence of Closing Resistor inside Circuit Breaker on Magnetizing Inrush Current of UHV Transformer

Using Matlab/Simulink software established the simulation model of UHV transformer and UHV power grid.The characteristic of magnetizing inrush current for UHV transformer was obtained by simulation.The paper also analyzed the impact on differential protection from it. Closing resistor inside circuit breaker method was proposed to restrain magnetizing inrush current.The method cuts down the amplitude and accelerated the attenuation speed of it, so as to restrain it. The simulation analysis verified the effectiveness of the method.

Method to Prevent the Malfunction Caused by the Transformer Magnetizing Inrush Current using IEC 61850-based IEDs and Dynamic Performance Test using RTDS Test-bed

The digital substations are being built based on the IEC 61850 network. The cooperation and protection of power system are becoming more intelligent and reliable in the environment of digital substation. This paper proposes a novel method to prevent the malfunction caused by the Transformer Magnetizing Inrush Current(TMIC) using the IEC 61850 based data sharing between the IEDs. To protect a main transformer, the current differential protection(87T) and over-current protection(50/51) are used generally. The 87T IED applies to the second harmonic blocking method to prevent the malfunction caused by the TMIC. However, the 50/51 IED may malfunction caused by the TMIC. To solve that problem, the proposed method uses a GOOSE inter-lock signal between two IEDs. The 87T IED transmits a blocking GOOSE signal to the 50/51 IED, when the TMIC is detected. The proposed method can make a cooperation of digital substation protection system more intelligent. To verify the performance of proposed method, this paper performs the real time test using the RTDS (Real Time Digital Simulator) test-bed. Using the RTDS, the power system transients are simulated, and the TMIC is generated. The performance of proposed method is verified in real-time using that actual current signals. The reaction of simulated power system responding to the operation of IEDs can be also confirmed.

Analysis of the Soft-Start Circuit of the High Voltage Power Supply Based on PSM Technology

The power supply based on pulse step modulation technology has been widely used as the high-voltage power supply (HVPS) for additional heating systems. The topology contains numbers of converters and multisecondary transformers. For the magnetizing inrush of the transformer and charging current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. There are resistor branches series with the transformer and each converter is used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, and as a result the dissipation and electromagnetic interference inside the module are serious. In this paper, the soft-start circuit is simplified to only one resistor branch. The precharge circuits of the converters, which are connected to the secondary, are diverted from the inside of the modules to the primary winding of transformer. Since the multisecondary transformer powers up at the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft-start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2-kV power supply, contains 12 converters, with soft start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft-start circuit of 100-kV HVPS system was designed.

A new algorithm based on Clarke's Transform and Discrete Wavelet Transform for the differential protection of three-phase power transformers considering the ultra-saturation phenomenon

This paper presents, at first, a novel model for investigating the ultra-saturation phenomenon during energization of a loaded three-phase power transformer. Then a new approach is presented to control the unusual false trip of a three-phase power transformer differential protection due to ultra-saturation phenomenon based on Clarke's Transform and Discrete Wavelet Transform (DWT). In this method, the transient phenomena of a power transformer including the magnetic inrush current, the ultra-saturation phenomenon, the external faults, and the internal faults of the power transformer are simulated. To distinguish between these phenomena, appropriate criteria based on Clarke's Transform and DWT are presented using the standard deviation of coefficients and the energy coefficients. The results of this study may be used as notifications by the personnel of substation and relay manufacturers.

A correlation based method for discrimination between inrush and short circuit currents in differential protection of power transformer using Discrete Wavelet Transform: Theory, simulation and experimental validation

This paper presents a new method for discrimination between magnetic inrush current and internal fault current in the differential protection of power transformer. The proposed method is based on the Wavelet Transform and correlation coefficient. In this study Discrete Wavelet Transform is used to describe the current signal in terms of different time and frequency components. In the proposed method, the energy signals of these components are employed. In the proposed method, a statistical parameter known as correlation coefficient is used to establish a criterion for the proposed discriminative algorithm. The correlation coefficient is used for express the relationship between wavelet coefficients energy at different scales of the signal resolution. Then pattern of these relations is utilized as a measure to discriminate the inrush current from fault current. For investigation the accuracy of the proposed algorithm different cases of inrush and internal fault currents is simulated by PSCAD/EMTDC software. Also, the proposed method is tested by the gathered data from experimental test at the laboratory. Current signals obtained from the simulation as well as the results obtained from the experimental test are employed by the proposed discriminative algorithm. Analysis of the simulation and experimental results show that the proposed method accurately identifies inrush and fault currents in the distance of the power transformer protection in a time period less than quarter of power frequency cycle. In addition to the sensitivity and high reliability, the proposed method has low computation work and does not required determining the threshold for each new power system.

Hyperbolic S -transform-based method for classification of external faults, incipient faults, inrush currents and internal faults in power transformers

In this study, a hyperbolic S-transform-based method is proposed to discriminate most important transient fault currents of transformers. First, the proposed method discriminates external faults from other disturbances. Then, the S-transform is applied to differential currents. An index is suggested by using absolute deviations of the S-matrix of differential currents to discriminate internal incipient faults in addition to inrush currents and internal faults. The relay issues an alarm signal in the case of the incipient fault but restrains during the magnetising inrush current. If an internal fault is recognised, the relay will issue a trip signal. To study the robustness of the suggested method, a program is developed in the MATLAB environment. The inputs of this program are differential current signals, derived from a system modelled by EMTP software. In order to simulate the internal incipient fault along with internal turn to turn and turn to earth faults, the transformer is modelled as 8×8 RL matrices, derived by using subroutine BCTRAN in EMTP. Also, differential currents are contaminated by noise and it is shown that the suggested method is not affected by noise and it can discriminate incipient faults, inrush currents, internal faults and external faults.

Voltage compensation-type inrush current limiter for reducing power transformer inrush current

When a transformer is initially energised, its iron core is driven into saturation, which will result in high-amplitude magnetising inrush current. For lessening this transient phenomenon, a voltage compensation-type inrush current limiter (VCT-ICL) is presented in this study. The VCT-ICL can automatically insert high impedance to restrain the sudden change in line current. After completing the restriction of inrush current, the VCT-ICL freewheels, and acts as a short circuit. Thus, other than performing the restriction, the VCT-ICL has a negligible effect in the circuit and the transformer seems to connect directly with the voltage source. When a load is connected at the secondary side of the transformer, to adjust the magnitude of DC reactor current so that it is equal to or higher than the peak of line current, there is almost no distortion to the load voltage and current waveforms during the steady state. A 5 kVA single-phase power transformer is used as an example to demonstrate the performance of the proposed limiter. According to the simulated and experimental results, the feasibility of the VCT-ICL has been verified. Moreover, increasing the insulation levels of the related components in the proposed limiter allows it to be applied in high-voltage distribution transformers.

Discrimination between inrush and fault condition in transformer: a probabilistic neural network approach

In this paper, an algorithm has been developed around the theme of the conventional differential protection of the transformer. The proposed algorithm is based on probabilistic neural network (PNN) and use of the spectral energies of detail level wavelet coefficients of differential current signal for discriminating magnetising inrush and fault condition in the transformer. Performance of the proposed PNN is investigated with the conventional backpropagation feed forward (BPFF) multilayer perceptron neural network. To evaluate the developed algorithm, relaying signals for various operating condition (i.e., inrush and fault) of the transformer, are obtained from a custom-built single-phase transformer in the laboratory.

Estimation of the Separate Primary and Secondary Leakage Inductances of a Y-Δ Transformer Using Least Squares Method

This paper proposes an estimation algorithm for the separate primary and secondary leakage inductances of a three phase <TEX>$Y-\Delta$</TEX> transformer using least squares method. The voltage equations from the primary and secondary windings are combined into a differential equation to estimate the separate primary and secondary leakage inductances in order to use the line current of the delta winding. Separate primary and secondary leakage inductances are obtained by applying least squares method to the differential equation. The performance of the proposed algorithm is validated under transient states, such as magnetic inrush and overexcitation, as well as in the steady state with various cut-off frequencies of low-pass filter. The proposed technique can accurately generate separate leakage inductances both in the steady and transient states.

Protection, faulted phase and winding identification for the three-winding transformer using the increments of flux linkages

The ratio of the increments of flux linkages (RIFLs) of the primary–secondary, primary–tertiary and secondary–tertiary windings is the same as the corresponding turns ratio during normal operating conditions, magnetic inrush and over-excitation. The RIFL differs from the turns ratio during an internal fault. In this study, the authors propose an algorithm for protection, a faulted phase and winding identification for the three-winding transformer using the increments of flux linkages (IFLs). The IFLs of each pair of windings are estimated for a single-phase and a three-phase transformer with wye-connected windings. For a three-phase transformer with delta-connected windings, the differences of the IFLs are estimated to use the line currents because the delta winding currents are practically unavailable. In this study, six detectors are suggested for fault detection; three additional detectors and a rule for the faulted phase and winding identification are presented as well. The proposed algorithm can not only detect an internal fault, but also identify the faulted phase and winding of a three-winding transformer. The various test results with electromagnetic transients program (EMTP) generated data show that the proposed algorithm successfully discriminates the internal faults from normal operating conditions including magnetic inrush and over-excitation. This study concludes by implementing the proposed algorithm into a prototype relay based on a digital signal processor.

Estimation of Delta Winding Current and Its Application to a Compensated-Current-Differential Relay for a Y-Δ Transformer

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 <TEX>$Y-\Delta$</TEX> transformer. This paper describes an estimation algorithm of the delta winding current and its application to a compensated-current-differential relay for a <TEX>$Y-\Delta$</TEX> 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.

A novel technique to discriminate inrush and fault in a single-phase transformer

This paper presents an algorithm based on a combination of Discrete Wavelet Transforms (DWTs) and Feed-Forward Artificial Neural Network (FFANN) to discriminate magnetising inrush from interturn fault. Interturn faults are staged on custom-built transformer. DWT is used for feature extraction from the differential current during magnetising inrush and interturn faults and FFANN is used to discriminate magnetising inrush from interturn fault. An online algorithm is tested successfully on the custom-built transformer. It is found that the proposed method gives satisfactory results, and may be useful in the development of modern differential relay for transformer protection scheme.

Theoretical Considerations of Magnetic Hysteresis and Transformer Inrush Current

This paper presents an application of a hysteresis model that is coupled to an equivalent network for the calculation of the inrush current due to an arbitrary excitation of a transformer after a fault. The approach proposed, although using several simplifying assumptions, seems promising in order to calculate the optimal time to close the circuit after a fault.

Radial basis probabilistic neural network for differential protection of power transformer

Protection of medium- and large-power transformers has always remained an area of interest of relaying engineers. Conventionally, the protection is done making use of magnitude of various frequency components in differential current. A novel technique to distinguish between magnetising inrush and internal fault condition of a power transformer based on the difference in the current wave shape is developed. The proposed differential algorithm makes use of radial basis probabilistic neural network (RBPNN) instead of the conventional harmonic restraint-based differential relaying technique. A comparison of performance between RBPNN and heteroscedastic-type probabilistic neural network (PNN) is made. The optimal smoothing factor of heteroscedastic-type PNN is obtained by particle swarm optimisation technique. The results demonstrate the capability of RBPNN in terms of accuracy with respect to classification of differential current of the power transformer. For the verification of the developed algorithm, relaying signals for various operating conditions of the transformer, including internal faults and external faults, were obtained through PSCAD/EMTDC. The proposed algorithm has been implemented in MATLAB.