Research and progress in developing key technologies for practical saturated iron-core superconducting fault current limiters

Abstract

Saturated iron-core superconducting fault current limiter is one of the various types of superconducting fault current limiters studied in recent years. The principle was first proposed by Raju’s group in the early 1980’s, which utilizes the intrinsic property of a magnetic core, i.e. change in magnetic permeability at different magnetization states, resulting in the change in impedance of the coil wound around it. There have been some technical difficulties for it to satisfy the utility’s requirement in functional capacity, safety, and reliability, which prevents this kind of device from practical application. This article introduces our progresses in solving these technical difficulties in last ten years. These progresses include: ensuring a deep and stable saturation of the iron-core’s working section by cross-sectional area variation of the core in a loose coupling structure, paving the way for high voltage grid applications; adopting a fast switching mechanism for the DC bias circuit to avoid high induced voltage during fault current limiting, protecting the device from damaging and enhancing its operation safety; by meas of the combination of high power mode and low power mode in magnetization and the use of varistor energy release unit, shortening the device’s recovery time to satisfy the grid re-closure requirement; taking on the three phases in one configuration to optimize the iron-core structure, reducing the size and the weight of the device and lowering the costs of manufacture, transportation and installation; eliminating the problem of induced eddy current and large coupling current on a metal oil-tank by using separated fiber glass oil-tanks. These new technologies make a saturated iron-core superconducting fault current limiter an ideal short-circuit fault current limiting device, a superior choice particularly for high voltage power grids.