Restricted earth fault protection for transformers using a directional element
AssigneeSchweitzer Engineering Laboratories, Inc.
InventorsArmando Guzman-Casillas, Luther S. Anderson
Life of this patent
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Abstract
The residual phase currents for each selected winding of a transformer are first determined and then summed to provide a value designated I.sub.X. The neutral current for the transformer is also determined, with the neutral current being designated I.sub.Y. A directional element calculates a torque value T according to the following formula: T=R.sub.e (I.sub.X .multidot.I.sub.Y *). This torque value will be negative for an external (reverse) fault, and positive for an internal (forward) fault. The quantity of the torque is compared against threshold values before a forward or reverse fault for the transformer is declared.
Claims14
A system for restricted earth fault protection for transformers, comprising:
- means for obtaining residual phase currents for selected windings of a transformer;
- means for summing the residual phase currents for said selected windings;
- means for obtaining the neutral current of said transformer;
- means for calculating a directional value using said summed residual currents and said neutral current;
- and
- means for evaluating the sign and quantity of the directional value to determine whether a fault exists and whether it is forward or reverse.
Dependencies are inferred from the claim text.