Correct Answer : Option (C) : Back-to-Back (Sumpner's Test)
Explanation : In the back-to-back test or Sumpner's test on a transformer, two identical transformers are connected in such a way that one transformer is kept onto another transformer. The primary side of the two identical transformers is connected in parallel across the supply voltage. In contrast, the secondary side of the transformer is connected in series in such a way that emf's are in series opposition. It is a method for determining the efficiency, voltage regulation and heading under loaded conditions of the transformer.
