Patent ID: 8553379

Claim:
A method for transformer differential protection, the method comprising: measuring a plurality of currents corresponding to a first set of windings of a transformer and a second set of windings of the transformer; compensating the plurality of measured currents based on their respective flows through either the first set of windings or the second set of windings, wherein the compensation is based on a model of an ideal current node, the model having equal current flow into and out of the current node under fault-free operation; calculating a differential current comprising a sum of the compensated currents; calculating a restraining current corresponding to the compensated currents; augmenting the restraining current by adding a value to the restraining current, the value based on at least one of a magnetizing inrush current and overexcitation of the transformer; calculating a complex current ratio corresponding to the plurality of compensated currents; applying an alpha plane analysis to the complex current ratio; and selectively tripping, based on the alpha plane analysis, a power apparatus that includes the transformer.