Which of the following is true concerning polarity?

• A. Identifies the positive and negative bushings
• B. Will identify if the transformer is a step up or step down
• C. A comparison of current direction in the primary vs. secondary windings at a given time
• D. An indication that a bushing is considered to be the north or south pole

Answer: (C)

Polarity is about whether the secondary voltage (and current) stays in step with the primary. It comes from how the windings are oriented and where the reference points (dots) are placed. To determine polarity, you compare the direction of current flow in the primary and secondary at the same moment. If the currents flow in the same sense relative to the dots, the voltages are in phase and additive when connected in series; if they flow in opposite senses, the voltages subtract.

This is why that option—comparing the current directions in the primary and secondary at a given time—best captures what polarity is and how it’s determined. Polarity isn’t about identifying which bushing is positive or negative, nor about whether the transformer steps up or down (that’s about voltage ratio), nor about magnetic north/south designation of a bushing.