Transformer differential protection

A system for transformer differential protection, the system comprising:

• a first terminal configured to measure a first plurality of currents flowing within a first set of windings of a transformer;
• a second terminal configured to measure a second plurality of currents flowing within a second set of windings of the transformer;
• and
• a processor configured to:
• compensate the first plurality currents based and the second plurality of 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;
• calculate a differential current comprising a sum of the compensated currents;
• calculate a restraining current corresponding to the compensated currents;
• augment 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;
• calculate a complex current ratio corresponding to the plurality of compensated currents;
• apply an alpha plane analysis to the complex current ratio;
• and
• selectively trip, based on the alpha plane analysis, a power apparatus that includes the transformer.

A system for transformer differential protection comprising:

• means for measuring a plurality of currents corresponding to a first set of windings of a transformer and a second set of windings of the transformer;
• means for 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;
• means for calculating a differential current comprising a sum of the compensated currents;
• means for calculating a restraining current corresponding to the compensated currents;
• means for 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;
• means for calculating a complex current ratio corresponding to the plurality of compensated currents;
• means for applying an alpha plane analysis to the complex current ratio;
• and
• means for selectively tripping, based on the alpha plane analysis, a power apparatus that includes the transformer.

A method for transformer differential protection 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;
• determining a voltage and a frequency applied to the transformer;
• calculating a volts per hertz (V/Hz) ratio based on the determined voltage and frequency applied to the transformer;
• comparing the V/Hz ratio to a threshold value;
• in response to the comparison, selectively augmenting the restraining current by adding a value based on the V/Hz ratio to the restraining current;
• and
• selectively tripping a power apparatus that includes the transformer based on a line current differential analysis using the differential current and the augmented restraining current.