Magnetizing inrush restraint method and relay for protection of power transformers
AssigneeGeneral Electric Company
InventorsAra Kulidjian, Bogdan Kasztenny
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Abstract
A method and relay for magnetizing inrush restraint in protective relays for power transformers. The method utilizes the phase angle relation between the fundamental component and the second harmonic in addition to the magnitude ratio. This is accomplished by calculating and utilizing the complex second harmonic ratio. The specially shaped operating characteristic for the complex second harmonic ratio is made dynamic providing for better security without jeopardizing dependability of the transformer protective relay.
Claims24
A method for providing protective control to a power transformer, comprising the steps of:
- receiving a plurality of input current signals;
- generating a differential current signal from the input current signals;
- generating phasor signals from the differential current signal, the phasor signals including a fundamental frequency component and a second harmonic component;
- generating a complex second harmonic ratio based on a magnitude and a phase angle of the fundamental frequency component and the second harmonic component;
- and
- defining an operating characteristic of a protective control device based on the complex second harmonic ratio.
A method of controlling a protective relay, comprising the steps of:
- calculating a complex second harmonic ratio based on magnitude and phase information for at least two phasor signals;
- applying an operating characteristic for the protective relay based on the complex second harmonic ratio, the operating characteristic including an operating region and a blocking region, the operating region expanding over time.
A protective relay, comprising:
- connections to an electrical system;
- processing circuitry configured to cause the protective relay to trip during an operating condition and to prevent the protective relay from tripping during a blocking condition,
- wherein the processing circuitry determines the operating condition and the blocking condition based on a complex second harmonic ratio derived from at least two phasors representative of a condition on the electrical system.
Dependencies are inferred from the claim text.