Besides voltage ratings and polarities, what other parameter must be identical when paralleling transformers?

When paralleling transformers, it's essential that the phase angles be identical. This is crucial because transformers operate based on alternating current and the phase angle determines the timing of the voltage waveforms. If the transformers have different phase angles, it could cause issues such as circulating currents between the units, leading to inefficient operation or even damage.

Using transformers with matching phase angles ensures that they are synchronized in terms of voltage waveforms. This synchronization allows them to share the load effectively without introducing harmful effects. For instance, if one transformer's phase angle differs by even a small amount, it can create imbalances that may adversely impact both transformers and the connected load.

Other parameters like core material, transformer weight, and winding type may affect overall performance and efficiency but are not as critical to the immediate process of safely and effectively paralleling transformers. Maintaining identical phase angles is fundamental to ensure they function harmoniously within the electrical system.