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If the primary voltage shows only the coil voltage, as in 2400, then the bushings can sustain only a limited voltage from the system ground, and the transformer must be connected phaseto-phase. 2 Single-Phase Secondary Connections Distribution transformers will usually have two, three, or four secondary bushings, and the most common voltage ratings are 240 and 480, with and without a mid-tap connection. 9 shows various single-phase secondary connections. 9 Single-phase secondary connections. 1 Two Secondary Bushings A transformer with two bushings can supply only a single voltage to the load.

Station service transformers (SST) that connect the system directly to the generator auxiliary load 3. Unit auxiliary transformers (UAT) that connect the generator directly to the generator auxiliary load In such a station, the UAT will typically be subjected to the most severe operational stresses. Abnormal conditions have been found to result from several occurrences in the operation of the station. 21 — between the UAT and the breaker connecting it to the auxiliary load — are fed by two sources, both through the UT from the system and from the generator itself.

Winding conductors were most likely made of copper from the very beginning. Several methods of insulating the conductor were used in the early days. Varnish dipping was often used and is still used for some applications today. Paper-tape wrapping of conductors has been used extensively, but this has now been almost completely replaced by other methods. , 1981). Although materials have improved dramatically, the basic concept of an oil-immersed cellulosic insulating system has changed very little in well over a century.