Transformer Differential Protection
Transformer differential protection is typically installed on transformers that are 10 MVA or larger [5].
At medium-voltage industrial facilities where the transformer wye windings are grounded through a grounding resistor, smaller transformers are generally protected by differential relays due to the sensitivity issues described in the “Transformer Basics” section.
Transformer differential protection is a challenge to apply due to factors like current magnitude and phase angle balancing, inrush and overexcitation restraint, and CT performance.
Digital relays have allowed manufacturers to improve many of the design elements that
comprise transformer differential protection.
Transformer differential protection can be divided into two categories: phase and ground.