Answer :
Final answer:
When converted to an autotransformer, a transformer's ratings such as terminal currents, KVA, and efficiency are altered, with capacity typically increasing. Exact calculations require additional data on transformer impedance.
Explanation:
When a transformer is changed from a standard two-winding arrangement to an autotransformer configuration, its rated capacities, such as terminal currents, KVA rating, and efficiency undergo changes. Using the given 450-kVA, 460-V:7.97-kV transformer specifications, we can perform some calculations to find the new ratings as an autotransformer. Here, the initial efficiency is 97.8% at rated load and unity power factor.
The key formulas involve assessing the increase in voltage and applying the autotransformer advantage, which affects the available KVA capacity. The current ratings depend on the KVA and voltage ratings. Unfortunately, without additional data, particularly the impedance of the transformer, exact efficiency calculations could be challenging.
Efficiency tends to remain similar if the autotransformer operation does not significantly alter current flows or alter losses proportionally to the increase in KVA.
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