US 6,356,421 B1 · System for power transformer differential protection

Abstract

Current transformer (CT) secondary currents for the windings of a power transformer are used to produce a differential current. An operating current value is obtained from the differential current value. A restraining current value is obtained from processed winding current values. Second and fourth harmonic values of the differential current are obtained and are summed with a restraining current quantity which is a result of the restraining current multiplied by a slope characteristic factor. If the operating current value is greater than the sum of the restraining current quantity and the second and fourth harmonic values, an output signal is produced which may be used as a trip signal unless it is blocked by selected blocking signals generated by another portion of the system.

Claims16

Dependent claims

A system for power transformer differential current protection, comprising:

means for developing a differential current value from processed winding current values which are representative of current transformer (CT) secondary current values obtained from the windings of a power transformer;
means for developing an operating current value from said differential current value;
means for developing a restraining current value from said processed winding current values;
means for obtaining at least one even harmonic value of said differential current value;
and
means for comparing the sum of the restraining current value and said at least one even harmonic value with the operating current value and for producing an output signal which in turn is useful in producing a trip signal when the operating current value is larger than said sum.

3 more elements

Dependencies are inferred from the claim text.

System for power transformer differential protection

Life of this patent

System for power transformer differential protection

Life of this patent

Abstract

Claims16