What is the standard polarity of a transformer less than 200 kva?

The standard polarity of a transformer less than 200 kVA is typically considered to be subtractive. This is based on the common practice in transformer design and installation. In subtractive polarity, if two transformers are connected in parallel and have the same phase rotation, the voltages are adjusted by subtracting one from another when they are out of phase. This helps in ensuring that the voltage levels remain stable and predictable when connecting multiple transformers to the same load.

Additive polarity is often used in larger transformers, while neutral and variable polarities do not specifically describe the standard practice for transformers of this size. Subtractive polarity provides a clear guideline for installation and operation, especially in systems where consistent voltage is critical. Therefore, understanding that subtractive polarity is the norm aids in the practical application of electrical systems using transformers under 200 kVA.