why we use battery source for current transformer polarity testing?

We use a battery source for current transformer (CT) polarity testing because it provides a stable and controlled DC voltage, ensuring accurate measurements. The battery eliminates potential interference from AC sources, allowing for clear identification of the CT’s polarity. By connecting the battery to the primary side of the CT, we can observe the output on the secondary side, confirming whether the phasing is correct and ensuring proper operation in the electrical system.