Saturated Core Fault Current Limiter Research Articles

Electrical insulation of high voltage inductor with co-axial electrode at floating voltage

Inductive fault current limiters (FCLs) have several advantages, such as significant current limitation, immediate triggering and relatively low losses. Despite these advantages, saturated core FCLs have not been commercialized due to its large size and associated high costs. A major remaining challenge is to reduce the footprint of the device. In this paper, a solution to reduce the overall footprint is proposed and discussed. In arrangements of windings on a core in reactors such as FCLs, the core is conventionally grounded. The electrical insulation distance between high voltage winding and core can be reduced if the core is left at floating potential. This paper shows the results of the investigation carried out on the insulation of such a coil-core assembly. Two experiments were conducted. In the first, the behavior of the apparatus under high voltage conditions was assessed by performing power frequency and lightning impulse tests. In the second experiment, a low voltage test was conducted during which voltages of different frequencies and pulses with varying rise times were applied. A finite element simulation was also carried out for comparison and further investigation.

Dynamic core length in saturated core fault current limiters

A saturated core fault current limiter (SCFCL) is a non-linear core-reactor where the core is saturated by an external superconducting DC bias source to achieve a low core permeability at nominal AC currents. Fault current levels in the AC coils de-saturate the core and transform it to a higher permeability state, hence limiting the fault current. In this work we describe the transition between saturated and de-saturated states in three SCFCL configurations. The ‘effective core length’, Leff, of the SCFCL, defined as the length of the de-saturated AC core limb, is introduced for exploring this transition as a function of the current, I, in the AC coil. Practically, Leff allows one to see the SCFCL as an inductor with a variable core length, allowing calculations of the impedance of the SCFCL over the whole range of operating currents. The Leff(I) curve is further used to calculate the dynamics of the demagnetization factor in a SCFCL. We show that the strong change in the magnetic induction of a SCFCL at high current is the result of both increasing the effective core length and decreasing the demagnetization factor. The method and results presented here serve as an important tool for comparing between various SCFCL concepts not only by comparing their impedance values at the extreme fault and nominal current conditions but also by providing an insight into the full de-saturation process.

Increasing Energy Efficiency of Saturated-Core Fault Current Limiters With Permanent Magnets

Fault current limiters are devices that limit currents in electrical networks during a fault event, such as power lines touching or arcing due to tree branches. In this paper, two designs for small-scale saturated-core fault current limiters are discussed: one that uses DC coils to saturate the cores, and one that uses a hybrid design with DC coils and permanent magnet blocks. The hybrid design is found to meet the same performance criteria with a 50% reduction in energy consumption when compared to the DC coil only design.

Experimental Analysis of the Magnetic Flux Characteristics of Saturated Core Fault Current Limiters

A fault current limiter (FCL) is a device that is designed to reduce the impact of fault currents on electricity networks and increase the availability of such networks to consumers. One particular FCL technology that is currently attracting worldwide attention, from both researchers and commercial engineering companies, is the saturated core FCL. This device utilizes the change in permeability between the saturated and unsaturated states of a magnetic core to provide both low steady state losses and effective fault current limiting. Typically the core is saturated using an electromagnetic coil, which can be either superconducting or non-superconducting. Although there have been several studies on the electrical characteristics of this device, the transient magnetic behavior has been largely overlooked. In this paper the magnetic flux characteristics of saturated core FCLs are experimentally analyzed. The study includes the magnetic behavior during both the initial biasing of the cores and during transient fault conditions. The influence of FCL topology and alternative low-cost core materials, on the flux characteristics and overall device performance, is also discussed.

Analytical Nonlinear Reluctance Model of a Single-Phase Saturated Core Fault Current Limiter

A saturated core fault current limiter (FCL) is a device that is designed to limit the fault currents in electrical energy networks and consequently, protect existing network equipment from damage. Due to complex nonlinear magnetic properties, the performance of saturated core FCLs has largely been characterized through experimentation and finite-element analysis simulations. Although both of these techniques are quite accurate, they are time consuming and do not describe the behavior of FCLs in actual electrical networks. This has led to an increasing demand for an accurate analytical model that is suitable for transient network analyses. This paper presents the development of an analytical model of a single-phase open-core FCL, which accurately describes the nonlinear magnetic properties of the FCL through a reduced reluctance approach. The extension of this model to other saturated core FCL arrangements (such as closed core) is also discussed.

Development and Deployment of Saturated-Core Fault Current Limiters in Distribution and Transmission Substations

Zenergy Power has been developing an inductive-type of fault current limiter (FCL) for electric power grid applications. The FCL employs a magnetically saturating reactor concept which acts as a variable inductor in an electric circuit. In March 2009 Zenergy Power, with funding from the California Energy Commission and the U.S. Department of Energy (DOE), installed an FCL in the Avanti distribution circuit of Southern California Edison's Shandin substation in San Bernardino, CA. Rated at 15 kV and 1,250 amperes steady-state, the “Avanti” device is the first superconductor FCL installed in a US utility. In January 2010, the “Avanti” device successfully limited its first series of real-world faults when the circuit experienced multiple single-phase and three-phase faults. After successfully validating the performance of a new “compact” saturated-core FCL, Zenergy Power received contracts to install a 12 kV, 1,250 amperes compact FCL in the CE Electric UK grid in early 2011 and a 138 kV, 1,300 amperes FCL at the Tidd substation of American Electric Power in late 2011.

High-temperature superconducting magnet for use in saturated core FCL

A HTS magnet system used in a saturated core Fault Current Limiter (FCL) device is described. The superconducting magnet, operating in DC mode, is used in such FCL design for saturating the magnetic core and maintaining low device impedance under nominal conditions. The unique design of the FCL poses constrains on the DC HTS magnet. A model which meets all the necessary special requirements have been realized in a compact magnet design that is optimized for its electrical characteristics while minimizing its mass and volume. The coil, made of Bi-2223 tapes, has 50000 Ampere-turns required to maintain the core in a saturated state at nominal current in the limiting circuit. Unique, nonmagnetic cryostat made of Delrin was used. Cooling of the coil has been realized by two cold heads: one double-stage head that provides a cooling power of 6 W at 20 K and a single-stage head with a cooling capability of 40W at 70 K. This magnetic system has been successfully integrated and tested in a 120 kVA FCL model. The design, characteristics and tests of this magnetic system are described.

Model of HTS three-phase saturated core fault current limiter

A small (several hundred watts) model of a three phase saturated core HTS fault current limiter (FCL) was developed and tested. Iron yokes of all three phases were saturated by a single DC HTS coil. The coil comprised a 60 turns single pancake (ID 135 mm), wound after heat treatment from Bi-2223 multifilamentary tape in Ag matrix. The critical current of the pancake in liquid nitrogen was 8 A. The tests have shown that the limiting value of the AC current (at 50 Hz) can be easily adjusted in the range from 8 A to 20 A depending on the value of the DC current in the HTS coil. The optimum value of the latter is 4 A, corresponding to the 8 times increase of the differential resistance in the current limiting mode. The response time is very short (less that 1 ms). Under tests the short-circuiting event was made in one, two and all three phases. The case of short-circuiting of one phase in the three-phase FCL is especially favorable from the standpoint of the voltages induced in HTS coil compared to the one-phase FCL.

Operating principle of a high Tc superconducting saturable magnetic core fault current limiter

An electrical fault current limiter (FCL) designed with a high Tc superconducting (HTS) dc bias winding is described. The winding is prepared by using a Ag-clad (Bi,Pb)2Sr2Ca2Cu3O10+x HTS wire. The limiting behaviour of this FCL is investigated and considered with respect to operation in a 6 kV power system. The results show that the FCL limits fault currents effectively, and is a possible solution for reducing power system fault currents.

Electrical application of high T/sub c/ superconducting saturable magnetic core fault current limiter

A saturable magnetic core electrical fault current limiter (FCT) designed with a high T/sub c/ superconducting (HTS) DC bias winding is described. The HTS winding is prepared by using a Ag-clad (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub O10+x/ HTS wire. The limiting behaviour of this FCL is investigated, and its electrical application is considered in an electrical power transmission system. The results show that this FCL limits fault currents effectively and is a possible solution for reducing power system fault currents.