Heinrich J. Boenig

Restoration and testing of an HTS fault current controller

A three-phase, 1200 A, 12.5 kV fault current controller using three HTS 4 mH coils, was built by industry and tested in 1999 at the Center Substation of Southern California Edison in Norwalk, CA. During the testing, it appeared that each of the three single-phase units had experienced a voltage breakdown, one externally and two internally. Los Alamos National Laboratory (LANL) was asked by DOE to restore the operation of the fault current controller provided the HTS coils had not been damaged during the initial substation tests. When the internally-failed coil vacuum vessels were opened it became evident that in these two vessels, a flashover had occurred at the high voltage bus section leading to the terminals of the superconducting coil. An investigation into the failure mechanism resulted in six possible causes for the flashover. Based on these causes, the high voltage bus was completely redesigned. Single-phase tests were successfully performed on the modified unit at a 13.7 kV LANL substation. This paper presents the postulated voltage flashover failure mechanisms, the new high voltage bus design which mitigates the failure mechanisms, the sequence of tests used to validate the new design, and finally, the results of variable load and short-circuit tests with the single-phase unit operating on the LANL 13.7 kV substation.

HTS high gradient magnetic separation system

We report on the assembly, characterization and operation of a high temperature superconducting (HTS) magnetic separator. The magnet is made of 624 m of Silver/BSCCO superconducting wire and has overall dimensions of 18 cm OD, 15.5 cm height and 5 cm ID. The HTS current leads are designed to operate with the warm end at 75 K and the cold end at 27 K. The system operates in a vacuum and is cooled by a two stage Gifford-McMahon cryocooler. The upper stage of the cryocooler cools the thermal shield and two heat pipe thermal intercepts. The lower stage of the cryocooler cools the HTS magnet and the bottom end of the HTS current leads. The HTS magnet was initially characterized in liquid cryogens. We report the current-voltage (I-V) on characteristics of the HTS magnet at temperatures ranging from 15 to 45 K. At 40 K the magnet can generate a central field of 2.0 T at a current of 120 A.

The bridge-type fault current controller - a new FACTS controller

The operation of a novel current controller, which can also function as a fault current limiter and as a solid-state AC circuit breaker, is presented. The controller, which consists of a thyristor bridge, an inductor and an optional bias power supply, is installed in series with the voltage source and the load. For load current values smaller than a preset value, the inductor of the current controller presents no impedance to the AC current flow. For values higher than the preset current value, the inductor is switched automatically into the AC circuit and limits the amount of current flow. Theoretical results in the form of circuit simulations and experimental results with a single-phase unit, operating on a 13.7 kV three-phase system with peak short-circuit currents of 3140 Arms, are presented.

Calorimeter for measuring AC losses in HTS cables for superconducting power transmission lines

We have developed a calorimeter with a sensitivity of better than 1 mW/m for measuring AC losses in HTS multi-strand conductors for superconducting power transmission lines over a temperature range of 64 K to 80 K. By choosing a temperature difference technique we eliminate the need for corrections due to heating at the cable end connections. Use of a three-phase configuration allows measurement of single-phase, three-phase, and coupling losses. The 60 Hz calorimeter power supply has a capacity of 2500 A rms.

Superconducting Fault Current Limiters

The sections in this article are 1 Electric Utility Grid Application 2 Quenching Types 3 Ferromagnetic Types 4 Semiconductor Types 5 Other Types 6 Superconductor Requirements 7 Cryogenics 8 Conclusion

Assembly and testing of a composite heat pipe thermal intercept for HTS current leads

We are building high temperature superconducting (HTS) current leads for a demonstration HTS high gradient magnetic separation (HGMS) system cooled by a cryocooler. The current leads are entirely conductively cooled. A composite nitrogen heat pipe provides efficient thermal communication, and simultaneously electrical isolation, between the lead and an intermediate temperature heat sink. Data on the thermal and electrical performance of the heat pipe thermal intercept are presented. The electrical isolation of the heat pipe was measured as a function of applied voltage with and without a thermal load across the heat pipe. The results show the electrical isolation with evaporation, condensation and internal circulation taking place in the heat pipe.

Anisotropic high temperature superconductors as variable resistors and switches

Several anisotropic high temperature superconductors show critical current densities which are strongly dependent on the direction of an applied external magnetic field. The resistance of a sample can change by several orders of magnitude by applying a magnetic field. The potential for using the field dependent variable resistor or switch for applications in power systems is evaluated. Test results with small samples are presented, The requirements for large scale applications are outlined. The magnetic field triggering requirement, the frequency response of the device, use in 60 Hz AC circuits and heat transfer considerations are investigated. Several application examples are discussed. Use of the variable resistor as a fault current limiter, as a switching element in rectifier circuitry and as an improved dump resistor for a superconducting magnet is presented.<<ETX>>

Single-phase AC losses in prototype HTS conductors for superconducting power transmission lines

The authors report single-phase ac loss measurements on 8, 4, and 3-layer, multi-strand, HTS prototype conductors for power transmission lines. They use both calorimetric and electrical techniques. The agreement between the two techniques suggests that the interlayer current distribution in one-meter long conductors are representative of those in long conductors. The losses for the 8 and 4-layer conductors are in rough agreement, with the 8-layer losses being somewhat lower. The 3-layer conductor losses are substantially higher--probably due to unbalanced azimuthal currents for this configuration.