Three-phase modeling of 40.5-kV vacuum circuit breaker switching off shunt reactors and overvoltage suppression measure analysis

The performance of vacuum circuit breakers (VCBs) in the interruption and protection of an electric power system is highly dependent on the contact conditions; thus, the assessment of the contact conditions is essential. The field emission current has been recognized as an effective parameter with which to investigate the contact conditions both qualitatively and quantitatively. The traditional measurement method that uses the field emission current to determine the contact conditions is performed under ac voltage and requires the VCB to be dismantled, which limits the application of this method. The objective of this study is to develop a new measurement method for the contact conditions in a VCB with the field emission current during the closing operation under dc voltage. The new measurement method does not require the VCB to be dismantled and can simplify the processing of experimental data. Then, the new measurement method is applied to investigate the contact conditions during capacitive switching. The obtained result shows that the field enhancement factor $\beta $ of the contact surface oscillates up and down during the capacitive experiment, which can verify the conditioning and deconditioning effects of the inrush current on contact surfaces.

A New Measurement Method of Contact Conditions in a Vacuum Circuit Breaker With the Field Emission Current During the Closing Operation

The article is concerned with analyzing the structure and properties of the Ni–C–Ag–N coating formed on copper by the complex method combining the electroexplosive spraying of coating, its irradiation by a pulsed electron beam and a subsequent nitriding in plasma of a gas discharge of low pressure. The structural constituents of coating's surface after the electroexplosive spraying as well as after the electron-beam processing and nitriding are studied. It is shown that a coating's thickness amounts to ≈90 μm. The wear resistance of a copper sample with the deposited coating exceeds that of the copper without the coating by ≈ 1.6 times. The friction coefficient of samples with the coating (μ = 0.5) is less than that of the copper without the coating (μ = 0.679) by ≈ 1.35 times. It is established that the hardness of the coating increases as the substrate is approached and reaches the maximum value of ≈1780 MPa (the hardness of substrate is 1300 MPa). By means of micro-X-ray-spectral analysis it is detected that the main chemical element of the coating is silver, but copper, nickel, carbon and nitrogen are present in a considerably smaller quantity. It is established by the methods of diffraction electron microscopy that the main phases of the coating are solid solutions. 

Increase in properties of copper electrical contacts in formation of composite coatings based on Ni-C-Ag-N system

Switching shunt capacitor banks is a challenging task for vacuum circuit breakers (VCBs). The objective of this article is to experimentally investigate the prestrike characteristics of single-break VCBs with cup-type axial magnetic field (AMF) contacts and spiral-type transverse magnetic field (TMF) contacts under inrush current conditions in four ways. These four aspects are: the prestrike gap probability distributions, the inrush current interruption phenomena, the prestrike electric field, and the contact erosion. The contact erosion is represented by the field enhancement factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> , which is obtained by the field emission current. The experimental results show that compared with the cup-type AMF VCB, the spiral-type TMF VCB is more effective since it can reduce 47.4% of the 50% prestrike gap, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d_{50}$ </tex-math></inline-formula> , and 28.6% of the scatter in prestrike gaps, which is mainly because the spiral-type TMF VCB can effectively reduce the contact erosion caused by inrush current. The spiral-type TMF VCB can significantly reduce the occurrence probabilities of inrush current interruption. The spiral-type TMF VCB can reduce 48.6% of the 50% prestrike arc time, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{a50}$ </tex-math></inline-formula> . The 50% prestrike electric field, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{\mathrm {pre50}}$ </tex-math></inline-formula> , of the spiral-type TMF VCB is 125% higher than that of the cup-type AMF VCB. For the controlled switching of capacitor banks, the spiral-type TMF VCB is superior to the cup-type AMF VCB. 

Prestrike Characteristics of Single-Break Vacuum Circuit Breakers With Cup-Type AMF Contacts and Spiral-Type TMF Contacts Under Inrush Current Conditions

Capacitive making of vacuum circuit breakers: Double-break vacuum circuit breaker is superior to single-break vacuum circuit breaker

The prestrike phenomenon in vacuum circuit breakers (VCBs) is interesting but complicated. Previous studies mainly focus on the prestrike phenomenon in single-break VCBs. However, experimental work on prestrike characteristics of double-break VCBs cannot be found in literature. This paper aims to experimentally determine the probabilistic characteristics of prestrike gaps in a double-break VCB consisting of two commercial vacuum interrupters (VIs) in series under direct current (DC) voltages. As a benchmark, single-break prestrike gaps were measured by short-circuiting one of the VIs in a double break. The experimental results show that the 50% prestrike gap d50 of each VI in a double break, which is calculated with the complementary Weibull distribution, was significantly reduced by 25% to 72.7% compared with that in a single break. Due to the voltage-sharing effect in the double-break VCB, scatters in prestrike gaps of each VI in a double break was smaller than that in a single break. However, without the sharing-voltage effect, d50 of the low-voltage side in the double break was 65% higher than that of the same VI in the single break, which could be caused by the asynchronous property of mechanical actuators, the difference of the inherent prestrike characteristics of each VI and the unequal voltage-sharing ratio of VIs.

Experimental Investigation of the Prestrike Characteristics of a Double-Break Vacuum Circuit Breaker under DC Voltages

Controlled switching of capacitor banks is an effective way to suppress the inrush current during capacitive-making operations. The objective of this paper is to determine the influence of the prestrike characteristics of four types of vacuum circuit breakers (VCBs) combined with two types of controlled switching strategies on the suppression effect of the inrush current. The four types of VCBs are cup-type axial magnetic field (AMF) single-break VCB, spiral-type transverse magnetic field (TMF) single-break VCB, cup-type AMF double-break VCB and spiral-type TMF double-break VCB. The prestrike characteristics of the four types of VCBs are investigated by synthetic tests. The two types of controlled switching strategies are the traditional controlled switching strategy (the closing command depends on the mechanical touch instant of the two contacts in VCBs) and the novel controlled switching strategy (the closing command depends on the 50% pre-arcing time ta50 of the VCBs). The results show that the spiral-type TMF double-break VCB combined with the novel controlled switching strategy is the best choice for applying back-to-back capacitor bank controlled switching. © 2017 Elsevier Inc. All rights reserved. 

A novel controlled switching strategy of back-to-back capacitor banks considering the prestrike characteristics of vacuum circuit breakers

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Papers

Three-phase modeling of 40.5-kV vacuum circuit breaker switching off shunt reactors and overvoltage suppression measure analysis

Experimental Investigation of the Prestrike Characteristics of a Double-Break Vacuum Circuit Breaker under DC Voltages

A novel controlled switching strategy of back-to-back capacitor banks considering the prestrike characteristics of vacuum circuit breakers