Frank Darmann

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 Edisons 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.

Properties of Ag–Mg alloy sheathed Bi-2223 tapes

Abstract The mechanical properties of 37 filament, pure Ag and Ag alloy (0.2 and 0.5 wt% Mg) sheathed Bi-2223 high temperature superconductor tapes were investigated. The use of Ag–Mg alloys enabled strengthening of the sheaths by an oxide dispersion strengthening (ODS) mechanism. The sheath hardness, tape tensile strength and the tolerance of the superconducting critical current to bending and axial strains increased with the concentration of the alloy addition. The sheath hardness results revealed evidence of overaging. Excessive hardening of the sheath, however, lead to the formation of rolling defects during the intermediate deformation stage of tape processing.

AC losses of filamentary HTS twisted filament round wires and flat tapes

Samples of multifilamentary Bi-2223/Ag/alloy twisted filament tapes and Z stack round wires, consisting of untwisted and twisted stacks (or z-arrays) of flat filaments have been prepared. It was found that twist pitches of less than 10 mm may be incorporated into multifilament tapes while maintaining the Jc at 20 kA/cm/sup 2/. The self-field AC loss has been investigated at low frequencies up to 100 Hz. The round wire was found to exhibit isotropic electromagnetic properties.

Determination of the AC losses of Bi-2223 HTS coils at 77 K at power frequencies using a mass boil-off calorimetric technique

A mass boil-off measurement system has been used to accurately measure and characterize the ac loss of high-temperature superconductor (HTS) coils at frequencies between 50 and 200 Hz, and in applied ac fields of up to 0.04 T. The mass boil-off calorimeter incorporated a glass cryostat, a copper field coil, and two mass flow meters. The response of the gas flow to a step change in the applied magnetic field was found to have a time constant of about 600 s. Under suitable experimental conditions, it was possible to measure the ac losses of coils with an accuracy of /spl plusmn/0.3 W. The ac loss characteristics of an HTS pancake and two HTS solenoid coils are presented and the accuracy of mass flow calorimetry in liquid nitrogen is reported on.

Results of AC loss tests on twisted and untwisted HTSC tape exposed to external field

This paper presents the results of magnetic loss tests on twisted and untwisted 37 multifilament tapes exposed to an alternating field at power frequencies. The losses are measured using calorimetric methods, which are capable of measuring losses in short tapes with the accuracy of several microwatts per centimeter of tape. The losses of the tape due to the longitudinal field of the untwisted tape agree well with theoretical calculations. The measurement results on the twisted filament tape, with 50-mm twist pitch, show that the losses are slightly lower than that in the untwisted tape. This is due to the reduction of the coupling losses between the filaments in the tape. It is also shown that in this presence of normal fields, the losses are about one order higher than for longitudinal fields because of the anisotropic properties of the superconducting parts and because of the existence of eddy current loss in the silver sheath.

Critical current and magnetic field performance of Bi-2223/Ag composite superconducting tapes

We report measurements of the electrical transport properties of ((BiPb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/-Ag) Bi-2223/Ag composite conductors produced as part of the long-length product development in an industrial plant. The powder-in-tube (PIT) process was used to manufacture conductors containing various filament configurations including monofilament and multifilament tapes with untwisted and twisted filaments, and round wires. The transport critical current I/sub c/ was measured at various temperatures (T=4-80 K) and magnetic fields (B=0-9 T) for different orientations of the tapes with respect to the field. Self-field transport ac losses were determined at 77 K and 60 Hz as a function of ac current amplitude (0-100 A rms). The strain performance was evaluated at 77 K for applied bend strains from zero to 1.5%.

Processing and characterisation of long-length silver/bismuth-2223 tape for electric power applications

The potential of high temperature superconductivity (HTS) to raise efficiencies in electric power utilisation is dependent on the availability of HTS materials in a form which can be engineered into devices. This paper reviews a program of continuous process and product improvement which has enabled tape with lengths up to 1000 m and appropriate engineering properties to be reproducibly processed using the powder-in-tube technique. Underpinning this development of a large scale process capability, tape development on a small scale was necessary in the areas of innovative tape design, metal forming optimisation and heat treatment. In addition, techniques for the characterisation of long lengths of tape were developed. These techniques included the modelling of the effect of the self-field generated by the tape under test at 77 K to enable zero field Ic data to be determined.

Calculation of the critical current in pancake-coiled long length Bi-2223/Ag tapes in non-uniform local magnetic fields perpendicular to the grain alignment axis

Abstract The DC magnetic field pattern of three pancake windings consisting of 150, 180 and 850 m of Bi-2223/Ag tape, was mapped within each winding volume. The analysis revealed a very non-uniform field distribution across the pancake width within each turn of the pancake. The effect of this non-uniform field across the tape width on the critical current of the pancake coil and on short sections within a single turn was measured. A model is proposed to explain the observed experimental data along with a method for correctly calculating the field free critical current

Design and loss calculations of a 100-kVA transformer employing multi-filamentary Bi-2223 Ag sheathed superconducting tapes

Abstract A dimensional analysis for the design of a 100 kVA, 3 phase, iron core, 6.6 kV/240 V, Wye–Wye connected transformer employing Ag sheathed Bi-2223 high-temperature superconducting (HTSC) multi-filament tapes has been carried out. The mass, volume and tape length requirements were calculated over a range of core cross-sectional areas. The objective of this exercise was to minimise the overall transformer volume. A range of suitable designs was then selected. Finite element methods software was used to map the magnetic fields throughout the winding volume of each design, and to estimate the hysteretic loss at full load. The analysis of mass and volume with core area variation showed the presence of distinct points, which would minimise these quantities. However, it was found that these designs were impractical in reality due to the significant length and cost of tape that they would entail. It was also shown that the coil electrical losses in these designs were too high due to the length of tape required and from the higher hysteretic loss. By considering the factors of mass, volume, hysteretic loss, and tape length and cost, a suitable design was found which was a compromise between all the factors involved. Assuming HTSC tape available with a modest Je of 5000 A/cm 2 , it was found that the mass and volume of the transformer could be reduced significantly compared to that of a conventional transformer. The volume decreased from 206 to 129 dm 3 and the dry mass decreased from 400 to 214 kg. The overall hysterises loss at full load was calculated to be 1290 W and the total length of tape required per phase is 1500 m. The minimum possible volume of the transformer for the given rating and engineering current density was found to be 83.8 dm 3 requiring 3508 m of HTSC tape.