Valerio Rossi

Test Results on 500 kVA-Class

The growth in generation and the increased interconnection of electrical grids lead to higher fault currents and therefore there is a considerable interest in fault current limiter (FCL) devices. In this work, we refer on the results of electrical testing on resistive-type superconducting FCL prototypes made by Ni-sheathed MgB2, developed in the framework of the Italian Project LIMSAT. This is the first time ever that short circuit testing results are reported on MgB2-based FCL prototypes at 27 K, cooled by a liquid neon bath. The time evolution of limited current and voltage across SFCL prototypes are reported and analysed. Critical aspects associated to the fault event such as the steep HTS tape temperature rise and electrical insulation at cryogenic temperature are also discussed.

{\rm MgB}_{2}

Since 2009, Ricerca sul Sistema Energetico S.p.A. has been involved in the development of a resistive-type superconducting fault current limiter (SFCL) for MV applications to be installed in the A2A Reti Elettriche S.p.A. distribution grid in the Milan area. The project started with simulations, design, and testing activities for a single-phase device; this first step paved the way for developing, testing, and live-grid installation at the hosting utility site of the final three-phase SFCL prototype. The result of this research activity is a resistive-type 9 kV/3.4 MVA SFCL device, based on first-generation (1G) BSCCO tapes, nowadays permanently installed as a single-feeder fault protection. This device is the first SFCL successfully installed in Italy. In this paper, we report on installation of the three-phase device and field-testing activity. The next step of the R&D activity will consist in the design of a three-phase SFCL demonstrator 9 kV/15.6 MVA to be installed at the same substation in an incoming feeder to limit the contribution of this feeder to the total short-circuit current of the network. This application is very demanding in terms of SFCL reliability and availability, but also the most interesting one for the A2A hosting utility needs.

-Based Fault Current Limiter Prototypes

The first Italian Superconducting Fault Current Limiter 9 kV/3.4 MVA was developed and lab tested by Ricerca sul Sistema Energetico S.p.A. and then installed in the Milan distribution grid belonging to A2A Reti Elettriche S.p.A. This resistive-type SFCL device was operational since March 2012 and hence has been field tested for more than two years, providing a large amount of experimental data with a significant experience gaining. Some preliminary results were already presented; however, this paper reports on the main outcomes of the field testing activity including the effective short-circuit current limitation provided by this SFCL prototype during a severe real three-phase short-circuit event in the Milan distribution grid. The SFCL device showed to behave as expected, promptly limiting the short-circuit current by a factor of about 2. This is the first SFCL limiting action in Italy and one of the very first worldwide. Further to this first successful installation, the hosting utility A2A agreed to install in the same substation a new SFCL device protecting four different feeders, therefore implying a SFCL upgrading up to 15.6 MVA. Therefore, this paper also anticipates the key steps towards the development of the upgraded SFCL prototype to be commissioned in early 2015.

Live-Grid Installation and Field Testing of the First Italian Superconducting Fault Current Limiter

The Superconducting Fault Current Limiter (SFCL) is a device of particular interest to electricity companies since it is aimed to maintain fault current levels on electricity networks to acceptable values, i.e. within electrical component design limits. The use of high temperature superconductors (HTS) allows the fabrication of effective SFCL devices with different configurations. In this work, we report on simulations and electrical testing of resistive-type SFCL prototypes. Short-circuit testing of several HTS windings has been carried out at CESI facility. Prospective symmetrical and asymmetrical fault currents 40 times larger than the nominal current value have been applied for 40-160 ms on single-phase devices. As a result, the prospective peak short-circuit current of 4,5 kA has been effectively reduced to 300 A-800 A depending of applied voltage. Time evolution of limited current, voltage across SFCL prototypes, dissipated energy and heating phenomena are reported and discussed.

Live Grid Field-Testing Final Results of the First Italian Superconducting Fault Current Limiter and Severe 3-Phase Fault Experience

Ricerca sul Sistema Energetico-RSE S.p.A. has recently accomplished a more than two-year-long in-field activity on the first Italian superconducting fault current limiter (SFCL). In order to carry out the in-field activity, a 9-kV/3.4-MVA SFCL device was installed as single feeder protection inside the Milan MV distribution grid; further to this first success, the development of a new device to be installed in the same substation, but as a transformer protection, has been already initiated. After having briefly summarized the final result of the in-field activity on the 9-kV/3.4-MVA device, this paper is mainly focused on the new 9-kV/15.6-MVA upgraded device: in particular, the first small-scale HTS winding prototypes will be described and the power tests implemented to validate their performances will be discussed. The test results allowed to identify the best layout, consisting in two parallel-connected coaxially arranged 2G windings, each made of two layers anti-inductively wound on a fiberglass cylinder, and each featuring a total 2G tape amount of 96 m. The actual research plan foresees to install the upgraded device in the live grid in 2016.

Simulations and electrical testing of superconducting fault current limiter prototypes

In the framework of the development of High Temperature Superconducting (HTS)-based solutions for modern power grids, Ricerca sul Sistema Energetico - RSE S.p.A. has gained a significant experience in design, testing, and installation of superconducting fault current limiters (SFCLs). After having successfully demonstrated the techno-economic feasibility of the first Italian three-phase BSCCO-based SFCL (9 kV/3.4 MVA) inside the distribution grid of A2A Reti Elettriche S.p.A. in the Milano area, RSE has initiated the development of a new upgraded three-phase SFCL, whose rated power has been enhanced in order to meet the utilitys needs. Unlike the first prototype, the new SFCL device (9 kV/15.6 MVA) is YBCO-based: this choice allows reducing the needed tape length and cooling power, saving at the same time a significant amount of operational costs. The first phase was already assembled and tested in 2015, whereas the second phase was tested in February 2016. This paper will show the last outcomes from characterizations and short-circuit tests. Along with the SFCL project, RSE has also been focusing on superconducting cables and, in the framework of the European Project Best Paths, it has been involved in DEMO5, that is dedicated to the development of a HTS DC cable in MgB2 (10 kA/3.2GW). Taking the cue from the DEMO5 requirements, RSE has initiated a parallel research activity that is focused on studying the thermo-fluid dynamic behavior of cryogenic coolants flowing in forced convection regime inside the flexible cryostat. This paper will present the first simulation results and will give some anticipation on next steps.

Status of Superconducting Fault Current Limiter in Italy: Final Results From the In-Field Testing Activity and Design of the 9 kV/15.6 MVA Device

The superconducting fault current limiter (SFCL) is the superconducting device for electrical applications closest to overcome the commercialization threshold. Device and operational costs due to resistive electrical connections and ac losses can be minimized by reducing superconducting tape length and power dissipation in the cryostat. Pursuing this goal, we realized anti-inductive coils of YBCO tapes without a copper stabilizing layer. The higher normal-state resistance allows considerable reduction of the necessary length, for the same current limitation factor. The focus of this work is on the soldering procedure and reinforcement of the superconducting tapes, which is particularly challenging when it is protected by only a 2-μm-thin Ag layer. Our developed procedure enabled the realization of the successfully tested single phases of the 9-kV/15.6-MVA resistive SFCL, currently under development at Ricerca sul Sistema Energetico-RSE S.p.A.