The concepts and focuses of two hot topics in the field of energy, namely integrated energy system and energy internet are summarized and analyzed.Typical research in the areas of integrated energy system and Energy Internet is reviewed.The research concerns and technologies of these two concepts are then outlined respectively.The differences and similarities of these two concepts and their future development are discussed.

A Brief Review to Integrated Energy System and Energy Internet 综合能源系统与能源互联网简述

DC power relay is a key electromechanical component widely used in electrical vehicles, photovoltaics, as well as more-electric aircrafts for energy managing, power conversion, and distribution. As the voltage and current increase due to relay switches, arc discharge becomes an unavoidable and significant issue during the operation of the dc high-power relay. Bridge-type contact and external permanent magnets are spontaneously employed in its arc chamber to accelerate the quenching of arc. In this paper, the complicated arc discharge plasma in a dc power relay has been investigated by using both experimental and numerical approaches. Initially, arc dwell and arc restriking characteristics during the arc motion phase are presented by analyzing the voltage and current waveforms and arc images acquired in carefully designed breaking experiments. The arc driven by a transverse magnetic field with a variety of flux densities and the influence of flux densities on arc voltage and dwell are preliminarily discussed based on the experimental results. Then, to reveal the arc physics and to determine the influence of transverse magnetic field on arc motion characteristics, a simplified model based on the magnetohydrodynamic (MHD) theory is built and three cases with different magnetic field are calculated. The simulated arc behaviors including distributions of the temperature and current density are presented. The mechanism underlying the influence of transverse magnetic field on the arc motion is analyzed according to arc root transfer and arc voltage variation. In addition, to understand the formation of the arc restriking, the critical breakdown electric-field strength inside the arc gap is also calculated based on streamer breakdown theory. The parameters in the space occupied by earlier arcs, as predicted by the MHD simulations, are used in the breakdown calculation. Results show that the critical breakdown voltage reduces remarkably along with growth of the operating voltage and breaking current, and the arc dwell time can be reduced by strengthening the external magnetic field within a reasonable extent.

Investigation on Arc Dwell and Restriking Characteristics in DC High-Power Relay

Arc Length of Break Arcs Magnetically Blown-out at Arc Extinction

The research on the heat source characteristics and the equivalent heat source of the arc in gaps

To obtain the dielectric recovery characteristics of 126 kV SF6 circuit breaker in repeatedly breaking and closing processes, we established an SF6 double-temperature arc plasma model due to the fact that ionizing is inadequate when current is small, and then used it in flow field calculation. According to the actual burning losses of the breakers, we also established mathematical models of electric field and flow field. In the light of the gas breakdown criterion in the streamer theory, we researched the breakers' dielectric recovery characteristic curves as well as the influences of contact wear on them. Furthermore, taking the extrusion and attrition of static contact attributed to moving arc contact into consideration, we analyzed the effect of burning loss on the electric field distribution in interrupter through three-dimensional electric field simulations. Results illustrate that contact burning loss obviously impacts critical breakdown voltage. It is obtained that, for a pair of contact spaced by 67 mm, compared with non-burning loss condition, when burning loss angle θ is 60°, the critical breakdown voltage is reduced by 180%. Plus the electric field distortion gets more severe with increasing θ: when θ is 80°, the electric field intensity at a point on static arc contact could reach 8.91 times as much as that of non-burning loss condition. Thereby, we proposed some methods to deal with the influences brought by contact burning loss on the dielectric recovery characteristics.

Dielectric Recovery Characteristics of SF_6 Circuit Breaker Considering Contact Burning Loss

The importance of high-power relays used to interrupt dc current has been significantly growing recently. In their arc chambers filled with nitrogen or its mixtures, bridge-type contacts with permanent magnets are major measures widely used for arc extinguish. Arc dwelling for a short duration after arc ignition, until its voltage increases rapidly, plays a crucial role in contact erosion. In this paper, arc dwelling time in a nitrogen environment during the entire bridge-type contacts interruption process of a resistive dc circuit is studied both experimentally and numerically. A multiphysics model coupled with the fluid flow, the temperature, the current density, as well as the E- and M-fields was built based on the magnetohydrodynamics theory for the arc chamber. The model was solved in COMSOL. The external resistive electric circuit was connected to the model, and the electric field in the arc was solved by adopting a floating potential. The detailed arc dwelling process is presented and preliminarily discussed according to the calculated temperature and current density distribution sequences. The calculated arc voltage shows good agreement with experimental results. Furthermore, the influence mechanism of breaking velocity on arc dwelling is analyzed by arc voltage. In this sense, the arc dwelling time could be shortened by increasing the breaking velocity within the reasonable extent.

Simulation of Arc Dwelling Behavior During Bridge-Type Contacts Opening Process for High-Power Relay

Arc plasma jet flow in the air was investigated under a bridge-type contacts in a DC 270 V resistive circuit. We characterized the arc plasma jet flow appearance at different currents by using high-speed photography, and two polished contacts were used to search for the relationship between roughness and plasma jet flow. Then, to make the nature of arc plasma jet flow phenomena clear, a simplified model based on magnetohydrodynamic (MHD) theory was established and calculated. The simulated DC arc plasma was presented with the temperature distribution and the current density distribution. Furthermore, the calculated arc flow velocity field showed that the circular vortex was an embodiment of the arc plasma jet flow progress. The combined action of volume force and contact surface was the main reason of the arc jet flow.

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Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts

Eutectic salts assisted synthesis of MOF-derived porous carbon as Pt–Sn catalyst support for ethanol oxidation reaction

Bridge-type contacts co-operated with permanent magnet are widely used in 270V/200A DC power relays. The permanent magnet helps to drive the arc out of contact gaps as soon as possible, and also helps to bend and quench the arc rapidly. Arc dwell stage is the first stage between arc ignition and the arc root moves out of the gap. This paper is focused on numerical investigation of dwell stage behaviors in bridge-type contacts in a 270V/200A DC power relay. A 2-D nitrogen arc model based on magneto-hydrodynamics theory is built and calculated. Basic dwell stage parameters are described by a set of coupled equations, including Navier-Stokes equation, energy equations and Maxwell equations. By adopting a floating potential, the voltage drop between movable contact and stationary contacts is solved. The detailed dwell stage behaviors are presented and preliminarily discussed according to the calculated temperature and arc current density distributions. Furthermore, experiments are carried out to validate the simulation results. The simulated arc voltage shows good agreement with that of acquired by experiments.

Kai Bo

Papers

Investigation on Arc Dwell and Restriking Characteristics in DC High-Power Relay

Simulation of Arc Dwelling Behavior During Bridge-Type Contacts Opening Process for High-Power Relay

Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts

Eutectic salts assisted synthesis of MOF-derived porous carbon as Pt–Sn catalyst support for ethanol oxidation reaction

Simulation on dwell stage of arcs in bridge type contacts for high-voltage DC relay