Detection of geomagnetically-induced currents with power line-mounted devices
A device for use in a power transmission system to sense GICs. The device may be a part of a reactance-injecting device on a power line, it may be a standalone device, or it may be a part of another type of device. The device may include a sensor to sense magnetic fields (e.g., a Hall effect sensor). The sensor may be positioned in the air gap of a magnetic core formed concentrically around the power line. The signal from the sensor may be converted to a digital signal and separately processed to determine the magnitude of the AC current and the magnitude of the DC (or quasi-DC) current. If the output signal of another A/C current sensor is available, that output signal may be used to adjust/calibrate the determined magnitude of the DC current. The sensor may communicate with other devices in a network to provide GIC information.
1. A device for monitoring geomagnetically-induced currents in a power transmission line, comprising:
a magnetic core disposed about a power transmission line, the core being configured to provide an air gap therein, wherein with the exception of the air gap, the magnetic core completely surrounds the power transmission line;
a magnetic sensor positioned in the air gap to sense magnetic fields and produce an output signal representative of the magnetic fields;
a signal processing unit that receives the output signal and determines the magnitude of a geomagnetically-induced current in the power transmission line therefrom; and
an injecting unit for injecting reactance into the power transmission line.
2. A device as claimed in claim 1 , further including an upper housing and a lower housing that are configured for placement around the power transmission line and for attachment to each other to contain the core, sensor, and signal processing unit therein.
3. A device as claimed in claim 1 , wherein the core includes at least two separate core portions.
4. A device as claimed in claim 1 , wherein the core includes at least three separate core portions.
5. A device as claimed in claim 4 , wherein one of the three separate core portions is configured to extend approximately 180 degrees around the power transmission line.
6. A device as claimed in claim 4 , wherein two of the three separate core portions are each configured to extend only approximately 90 degrees around the power transmission line.
7. A device as claimed in claim 1 , wherein the signal processing unit processes signals at or near DC with a DC processing portion.
8. A device as claimed in claim 7 , wherein the DC processing portion includes a low pass filter.
9. A device as claimed in claim 7 , wherein the DC processing portion includes a unit for determining the mean of the signals and providing a DC component signal representative thereof.
10. A device as claimed in claim 1 , wherein the signal processing unit separately processes AC signals and signals at or near DC with an AC processing portion and a DC processing portion, respectively.
11. A device as claimed in claim 10 , wherein the AC processing portion includes a unit for determining the RMS value of the signal and providing an AC component signal representative thereof.
12. A device as claimed in claim 10 , wherein the AC processing portion includes a high pass filter.
13. A device as claimed in claim 12 , wherein the AC processing portion includes a unit for determining the RMS value of the signal and providing an AC component signal representative thereof.
14. A device as claimed in claim 13 ,
wherein the AC processing portion includes a ratio-determining unit that determines the ratio of a reference signal to the AC component signal and produces a ratio signal representative thereof.
15. A device as claimed in claim 14 , wherein the reference signal is determined externally by a different AC current monitor.
16. A device as claimed in claim 1 , wherein the signal processing unit separately processes AC signals and signals at or near DC with an AC processing portion and a DC processing portion, respectively;
wherein the DC processing portion includes a unit for determining the mean of the signals and providing a DC component signal representative thereof;
wherein the AC processing portion includes a unit for determining the RMS value of the signal and providing an AC component signal representative thereof;
wherein the AC processing portion includes a ratio-determining unit that determines the ratio of a reference signal to the AC component signal and produces a ratio signal representative thereof; and
wherein the signal processing unit includes a multiplier unit that multiplies the DC component signal by the ratio signal.
17. A device as claimed in claim 1 , wherein the signal processing unit determines a DC component and an AC component; and
wherein the AC component is compared to a reference signal representative of an external measurement of the AC current in the power transmission line and, based on the comparison, the DC component is adjusted in proportion thereto.
18. A device as defined in claim 1 , wherein the device includes a transmitter and an antenna for communicating geomagnetically-induced current information to an external device.
19. A device as defined in claim 18 , wherein the external device includes a receiver for receiving information related to geomagnetically-induced currents.
20. A device as defined in claim 1 , wherein the device includes a current transformer for drawing current off of the power transmission line to provide operating power to the device.
21. A device as defined in claim 1 , wherein the magnetic sensor includes a Hall effect sensor.
22. A device as defined in claim 21 , wherein the output signal from the sensor is an analog signal and the device includes an analog-to-digital (A/D) converter.
23. A device as defined in claim 22 , wherein the analog signal is provided from the sensor to the A/D converter via a twisted pair of wires.
24. A device as defined in claim 1 , wherein the injecting unit includes a coil placed relative to the power transmission line in order to inject the reactance therein.
25. A device as claimed in claim 1 , wherein the magnetic sensor is electrically connected only to the signal processing unit.
26. A device as claimed in claim 25 , wherein the magnetic sensor is thus electrically isolated from ground.
27. A device for monitoring geomagnetically-induced currents in a power transmission line, comprising:
a magnetic core disposed about a power transmission line, the core being configured to provide an air gap therein, wherein with the exception of the air gap, the magnetic core completely surrounds the power transmission line;
a magnetic sensor positioned in the air gap to sense magnetic fields and produce an output signal representative of the magnetic fields; and
a signal processing unit that receives the output signal and determines the magnitude of a geomagnetically-induced current in the power transmission line therefrom;
wherein the magnetic sensor is electrically connected only to the signal processing unit and thus electrically isolated from ground.
28. A device as claimed in claim 27 , further including an upper housing and a lower housing that are configured for placement around the power transmission line and for attachment to each other to contain the core, sensor, and signal processing unit therein.
29. A device as claimed in claim 27 , wherein the core includes at least two separate core portions.
30. A device as claimed in claim 27 , wherein the core includes at least three separate core portions.
31. A device as claimed in claim 30 , wherein one of the three separate core portions is configured to extend approximately 180 degrees around the power transmission line.
32. A device as claimed in claim 30 , wherein two of the three separate core portions are each configured to extend only approximately 90 degrees around the power transmission line.
33. A device as claimed in claim 27 , wherein the signal processing unit determines a DC component and an AC component; and
wherein the AC component is compared to a reference signal representative of an external measurement of the AC current in the power transmission line and, based on the comparison, the DC component is adjusted in proportion thereto.
34. A device as defined in claim 27 , wherein the device includes a current transformer for drawing current off of the power transmission line to provide operating power to the device.