program abstracts
Thursday, 1A-09, 5:50-6:00
Conductor Requirements for HTS Utility Power Transformers
Vinay Mehrotra
E.F Pleva1 and S.W. Schwenterly2
1Waukesha Electric Systems, 400 S. Prairie Avenue,Waukesha, WI 53186-5969
2Oak Ridge National Laboratory, P.O. Box 2008, MS 6305, Oak Ridge, TN, 37831-6305
Tel. (262) 547-0121, Ext. 1427 Fax (262) 521-0139 E-mail Ed.Pleva@waukesha.spx.com
HTS coated conductors in utility power transformers must satisfy a set of operating requirements that are driven by two major considerations– HTS transformers must be economically competitive with conventional units, and the conductor must be robust enough to be used in a commercial manufacturing environment. Spreadsheet estimates of HTS transformer costs will be summarized and compared with those of conventional units that have been recently delivered by Waukesha Electric Systems. Lifetime cost of ownership is also determined by operating costs of ac losses, core losses, and lead heat loads, as well as periodic maintenance costs for the cryocoolers. Capital and operating costs can be traded off in the design stage to minimize the lifetime costs. These estimates allow us to predict the cost and allowable ac loss requirements in HTS coated conductors under various customer scenarios. HTS conductors in the transformer-manufacturing environment must have specific properties. Short-circuit currents can be an order of magnitude above the operating current, producing large forces and heating. Additional copper must be applied to the standard HTS tape to handle the forces and reduce heating. This can be either a co-wound strip or material that is directly plated or laminated onto the tape. The conductor must then be covered with a thick layer of high voltage insulation that is wound onto it in high-speed machines. Tension must be applied as the conductor is wound onto the coil form, and a certain amount of twisting and sideways deformation in the “hard” direction is needed to transition the conductor between pancakes. It must be possible to make joints and splices quickly and easily on the shop floor. Completed coils may need to be baked to remove moisture from the insulation. The transformer manufacturing process will be described in order to highlight these requirements.
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