The effects of forced flows at different velocities on microstructure and solute distribution during the directional solidification of Sn-10 wt% Bi alloys under a simultaneous imposition of a transverse static magneti...The effects of forced flows at different velocities on microstructure and solute distribution during the directional solidification of Sn-10 wt% Bi alloys under a simultaneous imposition of a transverse static magnetic field(TSMF) and an external direct current(DC) have been investigated experimentally and numerically. The experimental results show that the solid-liquid interface will gradually become sloping with the increase of the forced flow velocity when the thermoelectric magnetic convection(TEMC)dominates the forced flow at solidification front. However, the interface will gradually become planar as the flow velocity further increases when the electromagnetic convection(EMC) dominates the forced flow. Moreover, when the flow velocity gradually increases, the primary dendrite spacing decreases from384 to 105 μm accordingly. The simulation results show that the solute distribution at the two sides of the sample can be significantly changed by the forced flow at solidification front. The rejected solute will be unidirectionally transported to one side of the sample along the TEMC(a low-velocity forced flow),thereby causing the formation of a sloping interface. However, the rejected solute will be returned back along the EMC(a higher-velocity force flow), which results in a planar interface. Furthermore, the solute content at the two sides of the sample under the forced flows at different velocities was measured. The results are in good agreement with the simulation results, which shows that the solute content difference between the two sides of the sample reaches the maximum when a 0.5 T TSMF is applied, while the solute content difference decreases to zero with a simultaneous application of a 0.5 T TSMF and a 1.6 × 10~5 A/m^2 external DC.展开更多
For quickly clearing up a fault of distribution lines, which concerned with complex structure and operating modes, a directional comparison protection is necessary. The paper evaluated the traditional directional rela...For quickly clearing up a fault of distribution lines, which concerned with complex structure and operating modes, a directional comparison protection is necessary. The paper evaluated the traditional directional relay through modeling a typical distribution system and presented a novel negative sequence directional relay and a new directional comparison protection scheme specially designed for distribution systems. In the relay and the protection scheme, a particular negative sequence component has been constructed to solve the problem that there is no negative sequence component in a symmetrical fault case so that they could operate correctly in both asymmetrical fault and symmetrical fault. Extensive EMTP simulation studies proved that the protection schemes are able to provide fast and reliable responses for all fault conditions. In particular, they are able to give correct responses adapting to the change of system operation conditions, including the changing of system configuration, power flow direction, and source and tapped-offload conditions.展开更多
基金financially supported by the National Key Research and Development Program of China (No.2016YFB0301401)the National Natural Science Foundation of China (No.U1732276)+1 种基金the Science and Technology Commission of Shanghai Municipality (Key Project Nos.13JC1402500 and 15520711000)the Independent Research and Development Project of State Key of Advanced Special Steel,Shanghai University (Nos.SKLASS2015-Z021 and SELF-2014-02)
文摘The effects of forced flows at different velocities on microstructure and solute distribution during the directional solidification of Sn-10 wt% Bi alloys under a simultaneous imposition of a transverse static magnetic field(TSMF) and an external direct current(DC) have been investigated experimentally and numerically. The experimental results show that the solid-liquid interface will gradually become sloping with the increase of the forced flow velocity when the thermoelectric magnetic convection(TEMC)dominates the forced flow at solidification front. However, the interface will gradually become planar as the flow velocity further increases when the electromagnetic convection(EMC) dominates the forced flow. Moreover, when the flow velocity gradually increases, the primary dendrite spacing decreases from384 to 105 μm accordingly. The simulation results show that the solute distribution at the two sides of the sample can be significantly changed by the forced flow at solidification front. The rejected solute will be unidirectionally transported to one side of the sample along the TEMC(a low-velocity forced flow),thereby causing the formation of a sloping interface. However, the rejected solute will be returned back along the EMC(a higher-velocity force flow), which results in a planar interface. Furthermore, the solute content at the two sides of the sample under the forced flows at different velocities was measured. The results are in good agreement with the simulation results, which shows that the solute content difference between the two sides of the sample reaches the maximum when a 0.5 T TSMF is applied, while the solute content difference decreases to zero with a simultaneous application of a 0.5 T TSMF and a 1.6 × 10~5 A/m^2 external DC.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50077011 and 50377019) the National Basic Research Program of China ("973" Project) (Grant No. 2004CB217906)
文摘For quickly clearing up a fault of distribution lines, which concerned with complex structure and operating modes, a directional comparison protection is necessary. The paper evaluated the traditional directional relay through modeling a typical distribution system and presented a novel negative sequence directional relay and a new directional comparison protection scheme specially designed for distribution systems. In the relay and the protection scheme, a particular negative sequence component has been constructed to solve the problem that there is no negative sequence component in a symmetrical fault case so that they could operate correctly in both asymmetrical fault and symmetrical fault. Extensive EMTP simulation studies proved that the protection schemes are able to provide fast and reliable responses for all fault conditions. In particular, they are able to give correct responses adapting to the change of system operation conditions, including the changing of system configuration, power flow direction, and source and tapped-offload conditions.
