High-Voltage Power-Transformer Design----II

The previous part of this paper covered the initial development and application of the distributed concentric type of power transformer design. This type of design is chiefly suited for the larger sizes of power transformers in voltage classes of 138kv and up. This part deals further with the distributed concentric type transformer. Principal points covered are 1. Commercial impulse voltage testing is discussed. Impulse distribution tests made at low voltage have been adopted as standard commercial tests for distributed concentric type transformers. These tests determine the distribution of impulse voltage in the transformer winding for any specified shape of applied wave. Typical distribution tests are reported as taken on a commercial transformer. 2. A new form of insulating cylinder has been developed for application in the major insulation structure. The cylinder wall is unique in that it is porous and contains no bonding agent. This results in improved characteristics as compared to conventional type composition cylinders. The porous cylinder is made by a novel process which is illustrated and described. 3. Application of the basic design has been extended now to include transformers in the 138-kv, 161-kv, and 230-kv voltage classes. A particularly large transformer, weighing 250 tons complete, has been manufactured. Shipment was made to the Pacific Coast with the transformer proper assembled. The shipping clearance problem was met with a novel tank construction which is illustrated and described. 4.