For the first time, a high temperature superconducting (HTS) demonstration cable system has been installed in a utility network supplying electricity to consumers. The cable is a 30-m long, 30kVrms, 2, 000Arms cable, installed in the network of Copenhagen Energy at a substation supplying approximately 50, 000 customers. The purpose of the cable installation is to obtain installation and operating experience with this type of cable. The cable system has been in operation since May 28th 2001, and the first operating experiences of the cable have been satisfactory. The cable has been in operation for more than one year, and the cable has during the first year supplied 101, 000MWh of energy to the customers.
We fabricated MgB2 tapes and wires by a powder-in-tube (PIT) method, using MgB2 powder and several sheath materials such as Cu, Cu-Ni, Ni, pure Fe, carbon steel (Fe-C), and stainless steel. Jc of the as-cold rolled (un-sintered) tape significantly increased with the increase of total cross-sectional area reduction by the cold working. Hard sheath materials such as Fe-C and stainless steel are effective to enhance the packing density of MgB2 core and, therefore, to increase Jc values. Non heat treated MgB2 tapes with Fe-C and stainless steel sheaths showed extrapolated Jc values of-3.0-4.5×109A/m2 at 4.2K and zero field. Heat treatment after the cold rolling is effective to enhance Jc values. An order of magnitude higher Jc values were obtained for Fe, Fe-C, and stainless steel sheathed tapes after the heat treatment. Extrapolated Jc values well above 1010A/m2 at 4.2K and a zero magnetic field were obtained for stainless steel and Fe-C sheathed MgB2 tapes. Jc values of PIT-processed MgB2 tapes are less sensitive to strain than those of PIT-processed Bi-based oxide tapes. It is reported that the addition of soft metal powder such as In or Sn to the MgB2 powder is effective to enhance Jc values. We made -10m-long tapes with Ni sheaths, and fabricated small solenoid coil with this tape without sintering. The Ic of the coil was about 80% of the Ic of the short tape, indicating that the homogeneity of Ic in the 10m tape is fairly good. The coil generated 1.3kGauss at 4.2K.
Heat transfer property of Bi-2223/Ag multifilamentary tape impregnated with solid nitrogen was investigated by measuring the voltage and temperature traces on the tape. Solid nitrogen was produced by two different methods: i.e., one by conduction cooling with GM cryocooler, and another by evacuation with rotary vacuum pump. The heat transfer coefficient between the tape and the solid nitrogen was estimated based upon the numerical simulation. It was shown that the equivalent heat transfer coefficient of the tape impregnated with solid nitrogen made by conduction cooling at a very slow cooling rate was more than six times larger than that made by evacuation.