A: Polarity is the instantaneous voltage obtained from the primary winding in relation to the secondary winding. Transformers 600 volts and below are normally connected in additive polarity — that is, the terminals of the high voltage and low voltage windings on the left hand side are connected together, This leaves one high voltage and one low voltage terminal unconnected. When the trans¬former is excited, the resultant voltage appearing across a voltmeter will be the sum of the high and low voltage wind¬ings. This is useful when connecting single phase transform¬ers in parallel for three phase operations. Polarity is a term used only with single phase transformers