Modified method for transformer magnetizing characteristic computation and point‐on‐wave control switching for inrush current mitigation

Abstract

Summary This paper proposes a new model for the low‐frequency transient analysis of a transformer, with a modified equation for calculation of the flux‐current characteristic representing the saturation inductance of the transformer. The model is based on the V‐I (voltage‐current) no‐load curves and uses the no‐load reactive power losses. To validate the model, it was used to simulate the no‐load magnetizing current in steady‐state condition, as well as the transient inrush current at network frequency. Evaluation was done both by comparing the simulation results obtained with the proposed model and those available in the relevant literature, and by practical measurements. The experimental results presented in this paper were obtained via a laboratory setup and a data acquisition system based on the dSPACE board 1104. Moreover, a control switching to mitigate the transient inrush current in a transformer was developed and applied experimentally in the laboratory and also in the simulations. This control strategy was performed by taking into account the residual flux at the opening instant of the related circuit breaker. A comparative study was carried out showing the validity of the proposed model and the mitigation technique.

Transformer differential protection scheme based on self‐adaptive biased characteristic curve and considering cross‐country faults

“…Magnetic inrush current flows from the source to the transformer, sometimes up to 10–15 times the full load current, leading to differential protection performance 33 . In Yahiou et al, 34 a model for the low‐frequency transient analysis of a transformer, with a modified equation for calculation of the flux‐current characteristic representing the saturation inductance of the transformer was proposed. This control strategy was performed based on the residual flux value in order to inrush current mitigation at the switching instant of the transformer.…”

Point on Wave Energization Strategy and Sequential Phase Shifting for Sympathetic Inrush Current Mitigation in Three-Phase Transformer - Measurement

“…Using Faraday's laws, the flux wave is estimated from the voltage wave, and through it the residual flux is induced when the circuit breaker is opened. To reduce the values of the currents resulting from the influence of a transformer under the transient regime on already energized transformers, or the socalled sympathetic inrush current, the method that was proposed by the authors in (Yahiou et al, 2019) was exploited in this work. It is sufficient to calculate the value of the residual flux for only one phase U, and use it as a value to calculate the optimal time to close the circuit breaker without the appearance of the sympathetic calling current, without calculating the optimal time for the other phases V and W. Therefore, by exploiting the time of the phase U, the time of the V and W phases is calculated by adding the value of the phase shift 2*π/3 and 2*π/3 respectively.…”

Inrush Current Reduction by a Point-on-wave Energization Strategy and Sequential Phase Shifting in Three-Phase Transformer

“…To measure the inrush current in a three-phase transformer, a laboratory experimental setup with an acquisition system (dSPACE card) is detailed and presented in this article. The technique presented and proposed by Yahiou et al [20,21] has exploited to reduce the three-phase transformer transient current. This technique is based on Faraday's law to estimate the magnetic flux waveform via the voltage waveform, then the value of residual flux at the de-energizing moment (the circuit breaker is open) is estimated.…”

“…This technique is based on Faraday's law to estimate the magnetic flux waveform via the voltage waveform, then the value of residual flux at the de-energizing moment (the circuit breaker is open) is estimated. The main contribution of the present work is the exploitation of the method previously proposed by Yahiou et al [20,22], using a single phase transformer, to reduce the inrush current in three-phase transformers, where the residual flux value and the optimal time to close the circuit breaker for only the first phase (U) are calculated. For the other phases (V and W), the previous calculations are used.…”