Transformer through-fault current monitor
View Patent ↗A device is provided for monitoring through-fault current in an electric transformer on an electrical power system. The device generally includes a magnitude calculator for calculating the magnitude of current (e.g., a root means square value of current or magnitude of a fundamental of current) based on the current through the electric transformer. A through-fault energy calculator is further provided which is coupled to the magnitude calculator for calculating a through-fault energy value based on the magnitude of current or the calculated current through the transformer. An accumulator is coupled to the through-fault energy calculator for accumulating a plurality of through-fault energy values, and an alarm coupled to the accumulator for indicating that the accumulated through-fault energy values exceed a selected threshold.
1. A device for monitoring through-fault current in an electric transformer on an electrical power system, the electric transformer having a signal waveform therethrough, the device including:
a magnitude calculator adapted to calculate a magnitude value of current from the signal waveform based on the current flowing through the electric transformer,
a through-fault energy calculator coupled to the magnitude calculator adapted to calculate a through-fault energy value based on the magnitude value of current through the transformer, and
an accumulator coupled to the through-fault energy calculator for accumulating a plurality of through-fault energy values.
2. The device of claim 1 , wherein the magnitude calculator comprises a root means square calculator configured to calculate a root means square value of current, and wherein the magnitude value is the root means square value.
3. The device of claim 1 , wherein the magnitude calculator comprises a fundamental calculator configured to calculate a fundamental value of current, and wherein the magnitude value is the fundamental value.
4. The device of claim 1 wherein the accumulator begins accumulating through-fault energy values if the magnitude value of current exceeds a selected threshold.
5. The device of claim 4 wherein the transformer is a Class IV type transformer.
6. The device of claim 1 wherein the accumulator begins accumulating through-fault energy values if the magnitude value of current is greater than about 4.75 per unit.
7. The device of claim 1 further comprising an alarm coupled to the accumulator for indicating that the accumulated through-fault energy values exceed a selected threshold.
8. The device of claim 7 wherein the alarm is initiated if the accumulated through-energy value exceeds about 80%.
9. The device of claim 1 wherein the through-fault energy value is used as a fault severity indicator.
10. The device of claim 1 wherein the device is further adapted to provide a control signal to a power system element for isolating the transformer from the power system when the accumulated through-fault energy values exceed a selected threshold.
11. The device of claim 1 , further comprising a comparator in communication with the accumulator, configured to compare the accumulated value against a predetermined threshold.
12. The device of claim 11 , further comprising an output in communication with the comparator configured to block a reclosing operation when the accumulated value exceeds the predetermined threshold.
13. A method for monitoring an electric transformer on an electric power system, the electric transformer having a signal waveform therethrough, the method including the steps of:
sampling a signal waveform on either side of the transformer;
calculating a magnitude value of current based on the current through the electric transformer;
calculating a through-fault energy value based on the magnitude value of current through the transformer;
accumulating a plurality of through-fault energy values; and
determining whether the accumulated through-fault energy values exceed a selected threshold.
14. The method of claim 13 further including the step of providing an alarm if the accumulated through-fault energy values exceed a selected threshold.
15. The method of claim 13 further including the step of providing a control signal to a power system element to isolate the transformer from the power system if the accumulated through-fault energy values exceed a selected threshold.
16. The method of claim 13 , wherein the step of calculating a magnitude value comprises calculating a root means square value, and the magnitude value is the root means square value.
17. The method of claim 13 , wherein the step of calculating a magnitude value comprises calculating a fundamental value, and the magnitude value is the fundamental value.
18. A device for monitoring through-fault current in an electric transformer on an electrical power system, the electric transformer having a signal waveform therethrough, the device including:
a through-fault energy calculator adapted to calculate a through-fault energy value based on the signal waveform, and
an accumulator coupled to the through-fault energy calculator for accumulating a plurality of through-fault energy values.
19. The device of claim 18 further comprising a current magnitude calculator configured to calculate a magnitude of current through the electric transformer from the signal waveform, wherein the accumulator begins accumulating through-fault energy values if the magnitude exceeds a selected threshold.
20. The device of claim 19 , wherein the magnitude calculator comprises a root means square calculator.
21. The device of claim 18 further comprising an alarm coupled to the accumulator for indicating that the accumulated through-fault energy values exceed a selected threshold.
22. The device of claim 21 wherein the alarm is initiated if the accumulated through-energy value exceeds about 80%.
23. The device of claim 18 wherein the through-fault energy value is used as a fault severity indicator.
24. The device of claim 18 wherein the device is further adapted to provide a control signal to a power system element for isolating the transformer from the power system when the accumulated through-fault energy values exceed a selected threshold.