Patent ID: 6958894

Claim:
A relaying method for protecting a transformer comprising the steps of: 1) selecting a decision function based on one of a primary current of the transformer, a secondary current of the transformer, and a differential current therebetween: 2) determining a value of the decision function by measuring the primary current and/or the secondary current, and determining whether the value of the decision function is greater than a predetermined critical value at predetermined intervals; 3) memorizing a certain time point as a first detection time when the value of the decision function is initially determined as a value greater than the critical value at a certain time point or after a previous secondary detection time point; 4) determining as an inrush the case where the value of the decision function is detected as a value greater than the critical value at a certain time point before a predetermined time and after the first detection time point; and 5) determining as an internal fault the case where the value of the decision function is not detected as a value greater than the critical value at a certain time point after a predetermined time and the first detection time point, and generating a signal for driving a circuit breaker to protect the transformer.