Manufacturing and ordering of material for the active part of the transformer shall not proceed until the manufacturer has received final design approval from LES. LES reserves the right to perform a detailed independent review of the manufacturer's transformer design. The design review includes information described below and included in the LES design review template. The design review shall be at a location determined by LES (LES Facility, Manufacturer’s Facility, or Virtual Meeting). Manufacturer shall have appropriate members available for discussion of the design, quality assurance and manufacturing processes. • A winding arrangement diagram with the approximate clearances between windings and between windings and the ground planes shown on the diagram. • The type of windings to be used. • The type of conductors in each winding is to be listed. • A description of the transient analysis program used to calculate voltages between and within windings will be discussed. The margins used in the insulation design will be discussed. • A listing of the spaces between coils in shell form and between disks in core form. • The type of conductor insulation to be used. • A typical drawing or sketch of the insulation structure to be used should be available for the meeting. • Review methods used to make transpositions in windings. • Provide required manufacturer maintenance practices • Review LES’ maintenance practices. Do these meet the manufacturers’ requirements? • Outline the drying systems to be used and the degree of drying. • Description of the methods used to determine short circuit forces and stresses. The following will be discussed: - Inner winding free and forced buckling, radial bending, and axial bending for core form designs. Bending stresses for shell form. - Acceptance criteria for stresses. - Sizing and compression of windings will be presented in writing. - 0.2 % of yield of conductors. - Review of short circuit performance in service. - Compressive stresses on the radial spacers in each winding. • The following information is to be furnished on the thermal design. - Method used to calculate the hot spot temperatures. - Calculated top and bottom oil rise. The maximum oil rise in any cooling duct is necessary for both core and shell designs. - Calculated average and hot spot rises for each winding and all ratings. • Calculated impedances between all windings. • Furnish the type of core to be used, the maximum induction on any tap or winding combination, and the calculated core loss. • Furnish the calculated load losses on the guarantee and maximum loss positions. • Furnish the rating and manufacturer of bushings to be provided. • Provide the manufacture and ratings of DETC and load tap changers. • The mechanical design to withstand shipping forces will be discussed. • Leakage Flux Heating Analysis. - Tie plate, outer core laminations, tank wall, and frame heating in core form. - T-beam, frame, and tank wall shielding in shell form. - Heating around high current leads, high current bushings, and bushing turrets in both types of designs. - Review of potential circulating current heating in windings.
