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With the rapid development of the power system, the fault current becomes a big problem. The current limiting measures become more and more important. The saturated-core fault current limiter(SFCL) is one of the promising methods [1]. The most serious fault in electric power system is three-phase short-circuit fault, and the fault current is more likely to exceed the circuit breaker's capacity. The use of three single-phase current limiters at the same time will need a lot of ferromagnetic material and space. A compact three-phase SFCL was proposed in [2], but it cannot limit three-phase fault current [2]. So we propose a novel structure of Economical Three-phase Saturated-core Fault Current limiter(ETSFCL). The novel structure has good clipping performance at three-phase fault conditions. Compared to three single-phase SFCLs proposed in [3], it saves a lot of ferromagnetic material and reduces the AC flux through the permanent magnet. The stability of the permanent magnet is greatly improved and the risk of demagnetization is reduced. In this paper, the operating principle of the proposed structure is explained by analyzing its equivalent magnetic circuit and electrical circuit. FEA models were established in ANSOFT to verify the its effectiveness.

In order to protect high voltage direct current(HVDC) system from destructive damage caused by large DC fault current, a HVDC system saturable core type fault current limiter(DCSFCL) is proposed previously. However, through principle investigation and simulation analysis of DCSFCL, coil inductance of DCSFCL do not have a large changing rate (CR) when a fault occurs, so clipping performance of it will not be quite satisfying. In order to increase CR and improve clipping performance of original DCSFCL, further improvements need to be carried out. In this digest, a modified three limb structure of DCSFCL(TSFCL) is proposed and equivalent magnetic and electric circuit are analyzed. Simulations carried out on ANSYS shows that clipping performance is improved by a large scale.

The start current can reach up to as high as 4–7 times of the motor's rated current when high voltage motors start directly. For super large capacity motors (voltage above 6 kV, power above 10000 kW), the direct start current could reach 5000 Ampere or more [1]. Such large start current will not only have a huge impact on the motor itself but also cause a sudden decline of the grid voltage [2], [3]. In order to resolve this issue, a novel coupled auto-transformer and magnetic control (CATMC) soft starter method was proposed in this paper. The new structure of CATMC soft starter combines the two functions of the auto-transformer and the magnetic control reactor (MCR) through ingenious electric and magnetic circuit design. Hence the start current is reduced in two ways and the structure becomes more compact and flexible.

For future high voltage direct current (HVDC) grids, the dc protection system is often considered as one of th e main challenges due to the difficulty in interrupting a large dc current and the stringent time constraint imposed by the fast rising fault current[']. Therefore, a novel DC system fault current limiter based on saturable core reactor theory (DCSFCL) was proposed previously. In order to obtain better performance of DCSFCL that is unable to be accomplished by single magnetic material, mixed magnetic materials were applied to take advantages of different magnetic materials. Furthermore, magnetic valves were also added to original DCSFCL topology, which is a good way to optimize clipping performance and reduce the usage of both magnetic materials and permanent magnets (PM). ANSYS models were built and finite element analysis were carried out to verify the feasibility of these deductions.