If a transformer is rated 201 kva or above, what polarity is it considered to have?

Transformers that are rated 201 kVA or above are considered to have subtractive polarity. This classification relates to the way in which the windings are connected and how voltages add or subtract in the transformer. In subtractive polarity, the secondary voltage is effectively subtracted from the primary voltage when the transformer is connected in a specific configuration. This is particularly important when considering phase relationships in three-phase systems, as it helps prevent potential issues like phase cancellation or unstable voltage levels.

Understanding subtractive polarity is crucial for linemen and engineers because it impacts how transformers are connected in the field, ensuring that systems operate efficiently and safely. Recognizing the polarity of a transformer aids in proper installation and helps avoid complications that could arise from incorrect phasing, which can lead to electrical faults or failures.