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Recently, the grounding system of substation has been seriously invaded by earth current generated by flourishing urban rail transit network. The invasion leads to abnormal vibration of transformer and even some electrical safety problems. This article presents a dc and harmonic current suppression system (DHSS) applied to the neutral point of transformer. The design and development of the DHSS are described in detail. The power circuit is designed as a segmented structure with dc current blocking and harmonic current suppression. The high-speed bypass protection circuit is implemented to ensure the reliable grounding of neutral point in any case. The matching control and protection system is developed. The proposed controller for suppressing harmonic current is applicable for the neutral point and meets the requirements of relay protection. The design details and difficulties are discussed. The development, commissioning, and experiment are completed in the laboratory. The developed prototype has been subjected to high current impulse tests. The performance and reliability are verified by the presented results. This prototype is running on-site in a 220 kV substation. [ABSTRACT FROM AUTHOR]

Earth current generated by the operation of urban rail transit can enter into the neutral point of grounding transformer, which will result in the deterioration of transformer operation performance and cause electrical safety problems. In this article, the neutral current for 220 kV transformers has been measured in the real power system, the characteristics of dc and harmonic current are analyzed, and a novel suppression method for the dc and harmonic current simultaneously combining an active converter with a dc blocking capacitor is proposed, which solves not only the traditional dc bias problem but also the intrusion of the harmonic current from urban rail transit. The active converter is designed to compensate harmonic voltage to suppress harmonic current, and the capacitor provides blocking for the dc current. The protection scheme in case of the high fault current of the neutral point is presented. The improved control method is designed to control the neutral current and adjust the fundamental impedance for the requirements of relay protection. The effectiveness of the proposed method is verified by the digital simulations and the laboratory experiments based on the field working conditions, and the results demonstrate the satisfying performances. [ABSTRACT FROM AUTHOR]

Based on a steady-state 3-D magnetohydrodynamic (MHD) model, the high-current vacuum arc (HCVA) under combined effect of actual magnetic field (MF) and external transverse MF (ETMF) is simulated. The actual MF is generated by cup-type axial magnetic field contact system commonly used in commercial vacuum circuit breakers. The ETMF may cause the deflection of arc column, which is the main reason of the contact deflected erosion. According to some experimental results, the electron temperature in HCVA is assumed to be uniform and equal to 3 eV. Therefore, the MHD model is simplified by neglecting the electron energy equation to improve the simulation efficiency. With the three conservation equations (mass, momentum, and energy) of ion flow coupling solved, the spatial distributions of some flow parameters can be obtained. The influence of all three components of the MF is inserted by solving the magnetic transport equations sequentially. Proper boundary conditions are set on the cathode and anode side, which separated the cathode spots mixing region and anode sheath region from computation domain, respectively. Under the influence of the ETMF, the deflection of the plasma flow can be predicted, which may be helpful to understand the mechanism of the contact deflected erosion. [ABSTRACT FROM PUBLISHER]

In this paper, a transient 3-D model of the anode activity in a high-current vacuum arc (HCVA) was established. The melting, flow, evaporation, and solidification of the anode material were included in this model. Based on this model, the thermal and flow process of the anode in an HCVA under axial magnetic fields was simulated and analyzed. Simulation results showed that the maximum anode temperature appeared near 7 ms. The maximum rotational velocity and melting radius appeared near 9 ms. This meant that the anode was still in the melting, flow, and evaporation status near current zero moment, which was easier to cause reignition of vacuum interruption. Through 3-D modeling and simulation, a more visualized anode process can be understood. In the future, unsymmetrical anode phenomena will be researched and analyzed by this 3-D model. [ABSTRACT FROM PUBLISHER]

Based on a 3-D steady magnetohydrodynamic model, the high current vacuum arc subjected to a realistic spatial magnetic field generated by the cup-type contacts was simulated. The influence of the realistic spatial magnetic field profile on plasma's rotation behavior was analyzed. The distribution of the azimuthal velocity on anode side under realistic spatial magnetic field profile was quite different from that under uniform axial magnetic field. [ABSTRACT FROM PUBLISHER]