Detection of geomagnetically-induced currents with power line-mounted devices

Abstract

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 NC 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.

What is claimed is: 
     
         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; 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 isolated from ground.   
     
     
         2 . A device as claimed in  claim 1 , wherein the magnetic sensor is electrically connected only to the signal processing unit. 
     
     
         3 . A device as claimed in  claim 1 , further including an upper housing and a lower housing that are configured for placement around a power line and for attachment to each other to contain the core, sensor, and signal processing unit therein. 
     
     
         4 . A device as claimed in  claim 1 , wherein the core includes at least two separate core portions. 
     
     
         5 . A device as claimed in  claim 1 , wherein the core includes at least three separate core portions. 
     
     
         6 . A device as claimed in  claim 5 , wherein one of the three separate core portions is configured to extend approximately 180 degrees around the power line. 
     
     
         7 . A device as claimed in  claim 5 , wherein two of the three separate core portions are each configured to extend approximately 90 degrees around the power line. 
     
     
         8 . A device as claimed in  claim 1 , wherein the signal processing unit processes signals at or near DC with a DC processing portion. 
     
     
         9 . A device as claimed in  claim 8 , wherein the DC processing portion includes a low pass filter. 
     
     
         10 . A device as claimed in  claim 8 , wherein the DC processing portion includes a unit for determining the mean of the signals and providing a DC component signal representative thereof. 
     
     
         11 . 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. 
     
     
         12 . A device as claimed in  claim 11 , wherein the AC processing portion includes a unit for determining the RMS value of the signal and providing an AC component signal representative thereof. 
     
     
         13 . A device as claimed in  claim 11 , wherein the AC processing portion includes a high pass filter. 
     
     
         14 . A device as claimed in  claim 13 , wherein the AC processing portion includes a unit for determining the RMS value of the signal and providing an AC component signal representative thereof. 
     
     
         15 . A device as claimed in  claim 14 , 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. 
     
     
         16 . A device as claimed in  claim 15 , wherein the reference signal is determined externally by a different AC current monitor. 
     
     
         17 . 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.   
     
     
         18 . 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 line and, based on the comparison, the DC component is adjusted in proportion thereto.   
     
     
         19 . 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. 
     
     
         20 . A device as defined in  claim 19 , wherein the external device includes a receiver for receiving information related to geomagnetically-induced currents. 
     
     
         21 . A device as defined in  claim 1 , wherein the device includes a current transformer for drawing current off of the power line to provide operating power to the device. 
     
     
         22 . A device as defined in  claim 1 , wherein the magnetic sensor includes a Hall effect sensor. 
     
     
         23 . A device as defined in  claim 22 , wherein the output signal from the sensor is an analog signal and the device includes an analog-to-digital (ND) converter. 
     
     
         24 . A device as defined in  claim 23 , wherein the analog signal is provided from the sensor to the ND converter via a twisted pair of wires. 
     
     
         25 . A device as defined in  claim 1 , wherein the device includes an injecting unit for injecting reactance into the power line. 
     
     
         26 . A device as defined in  claim 25 , wherein the injecting unit includes a coil placed relative to a power line in order to inject the reactance therein. 
     
     
         27 . A method of operating a power transmission system having a power transmission line, comprising:
 placing a magnetic core onto the power transmission line of the power transmission system, 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;   positioning a magnetic sensor in the air gap to sense magnetic fields and produce an output signal representative of the magnetic fields, wherein the magnetic sensor is electrically isolated from ground; and   receiving the output signal and determining the magnitude of a geomagnetically-induced current in the power transmission line therefrom.   
     
     
         28 . A method as defined in  claim 27 , further including sending a communication based on the determining the magnitude step to a first component of the power transmission system. 
     
     
         29 . A method as defined in  claim 28 , wherein the first component of the power transmission system is remotely located from the location where the magnetic core and the magnetic sensor are located