Abstract
In this paper, a DC fault short circuit was conducted to analyze the DC fault current limiting characteristics of a flux-coupling type superconducting fault current limiter (SFCL) that has two coils connected in series via one iron core. Similar to the AC power system, the flux-coupling type SFCL in a DC system, which has the two coils connected with each other in series and the secondary coil connected with the superconducting element in parallel, remains in the superconducting state before a short-circuit accident occurs. This results in magnetic flux getting generated by the two windings connected in series offsetting each other and the induced voltage at the two windings remaining at zero. However, in the event of a short-circuit accident on the DC line, a resistance is generated on the superconducting element, so that the magnetic flux generated at the two windings no longer offsets each other. Therefore, a voltage is induced on the two windings, and the fault current is limited accordingly. As a result of configuring a DC short-circuit device and experimenting with this SFCL, we could confirm the DC fault current limiting effect of a flux-coupling type SFCL with two windings connected in series. In addition, we could establish performance conditions of the flux-coupling type SFCL in a DC system by inferring the fault current, operating current, and limited impedance equations according to the connection direction of the flux-coupling type SFCL with two windings connected in series and by analyzing fault current limiting degree, power burden, magnetic flux, and energy consumption for each element composing the SFCL.
Highlights
The increase in power demand and power supply facilities in DC systems, as well as AC systems, has increased the fault current of the system, and in an increasing number of places, the short-circuit capacity of existing circuit breakers is exceeded
We built a flux-coupling type superconducting fault current limiter (SFCL) prototype connected in series between two coils to limit the DC fault current in a DC system and constructed a DC simulated short-circuit accident device for an experiment
We compared the characteristics of the fault current limiting and the power burden before and after DC failure according to the winding direction of the two coils
Summary
The increase in power demand and power supply facilities in DC systems, as well as AC systems, has increased the fault current of the system, and in an increasing number of places, the short-circuit capacity of existing circuit breakers is exceeded. The topics of some published papers have been limited to evaluating optimization and economic feasibility and focus on deriving impedance values without considering the recovery characteristics of SFCL [33–39] They analyze DC current-limiting factors focusing on simulations rather than experiments to present applications [40–44]. In this paper, we intended to analyze the fault current-limiting effect of a flux-coupling type SFCL that has two coils connected in series via one iron core for inducting simultaneous quenching to reach a uniform power burden on the superconducting elements that make up flux-coupling type SFCL in a DC system when its capacity is increased. We intended to measure the quench of superconducting elements from a simulated DC short-circuit experiment and to compare and analyze the current and voltage relationships of flux-coupling type SFCL and the changes in various characteristics of each winding before and after the fault.
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