Substation1
Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

additive polarity
polarity designation of a transformer in which terminals of the same polarity on the low-and high-voltage coils are physically adjacent to each other on the transformer casing. With additive polarity, a short between two adjacent terminals results in the sum of the two coil voltages appearing between the remaining terminals. Additive polarity is generally used for transformers up to 500kVA and 34.5kV. Larger units use subtractive polarity.
See subtractive polarity