System and Apparatus for Detecting Faults in an Insulation Layer of a Buried Conductor

Abstract

Methods, systems and locators for detecting faults in an insulation later of an insulated conductor buried beneath a ground surface are described. The locator comprises a magnetometer arranged to detect a magnetic field generated by the alternating current and to generate a current signal on the basis of the detected magnetic field, and an Alternating Voltage Gradient receiver comprising a pair of probes arranged to make electrical contact with the ground surface, which is arranged to generate a voltage signal indicative of a voltage between the pair of probes. A processor is configured to substantially synchronously sample the current signal and the voltage signal. This enables improved detection of faults in the insulation layer of the insulated conductor.

What is claimed is: 
     
         1 . A locator for detecting faults in an insulation layer of an insulated conductor buried beneath a ground surface, the insulated conductor carrying an alternating current, the locator comprising:
 a magnetometer arranged to detect a magnetic field generated by the alternating current and to generate a current signal on the basis of the detected magnetic field;   an Alternating Voltage Gradient receiver comprising a pair of probes arranged to make electrical contact with the ground surface, the Alternating Voltage Gradient receiver being arranged to generate a voltage signal indicative of a voltage between the pair of probes;   a processor configured to simultaneously sample the current signal and the voltage signal; and   a user interface configured to simultaneously display the sampled signals.   
     
     
         2 . A locator according to  claim 1 , wherein the processor is configured to determine a phase difference between the current signal and voltage signal. 
     
     
         3 . A locator according to  claim 2 , comprising a memory, wherein the processor is configured to store in the memory current measurements based on the processed current signal, voltage measurements based on the processed voltage signal and a phase measurement based on the determined phase difference between the current signal and voltage signal. 
     
     
         4 . A locator according to  claim 3 , comprising a position locating device arranged to determine a position of the locator, wherein the processor is configured to store, in the memory, position information relating to the position of the locator when stored current and voltage measurements were measured. 
     
     
         5 . A locator according to  claim 4 , wherein the processor is configured to determine a rate of phase difference with respect to distance determined on the basis of the position information. 
     
     
         6 . A locator according to  claim 3 , comprising a communications interface for communicating with a portable computing device, wherein the processor is configured to transmit the current and voltage measurements to the portable computing device. 
     
     
         7 . A locator according to  claim 4 , wherein the processor is configured to transmit the current and voltage measurements to the portable computing device in real time. 
     
     
         8 . A locator according to  claim 2 , wherein the processor is configured to, in use, obtain survey measurement data, the survey measurement data comprising, for each of a plurality of different positions along a survey path traversed by the locator, a current measurement based on the current signal and a voltage measurement based on the voltage signal. 
     
     
         9 . A locator according to  claim 8 , wherein the survey measurement data further comprises, for each of the plurality of different positions along the survey path traversed by the locator, a phase difference measurement of the phase difference between the current signal and the voltage signal. 
     
     
         10 . A locator according to  claim 9 , wherein the processor is configured to determine, based upon a variation in the phase difference measurements with distance over a section of the survey path, information regarding the length of a fault located in an insulation layer of an insulated conductor buried beneath the ground surface under the survey path. 
     
     
         11 . A locator according to  claim 10 , wherein the information is an estimate of the length of the fault. 
     
     
         12 . A locator according to  claim 9 , wherein the locator comprises a display and the processor is configured to cause a plot of at least one of: the current measurements; the voltage measurements; and the phase difference measurements against distance to be displayed on the display. 
     
     
         13 . A locator according to  claim 8 , comprising a communications interface for communicating with an external computing device, wherein the processor is configured to transmit the current and voltage measurements to the portable computing device. 
     
     
         14 . A locator according to  claim 12 , wherein the external computing device is a portable computing device. 
     
     
         15 . A locator according to  claim 10 , wherein the alternating current carried in the insulated conductor has a low frequency component and a relatively higher frequency component, and wherein the magnetometer is arranged to detect the magnetic field generated by the low frequency component. 
     
     
         16 . A locator according to  claim 15 , comprising two magnetic field sensors each configured to generate a magnetic field signal in response to a magnetic field generated by the high frequency component, wherein the processor is configured to determine a depth of the insulated conductor based on the generated magnetic field signals. 
     
     
         17 . A locator according to  claim 1 , wherein the simultaneous sampling causes a survey to be done quicker by being performed in one pass of the buried conductor. 
     
     
         18 . A locator according to  claim 1 , wherein the current signal is used to determine a current in the buried conductor. 
     
     
         19 . A locator according to  claim 10 , wherein the locator comprises a detector for locating the insulated conductor and the magnetometer is affixed to the detector and the Alternating Voltage Gradient receiver is mounted in a frame separate to the detector,
 wherein, in use:
 the detector is to be carried in a first hand of an operator; and 
 the frame is to be held in a second hand of the operator, different to the first hand. 
   
     
     
         20 . A method for detecting faults in an insulation layer of an insulated conductor buried beneath a ground surface, the method comprising:
 applying an alternating current to the buried conductor;   simultaneously (i) detecting a magnetic field generated by the alternating current with a magnetometer located above the ground surface and (ii) measuring a voltage between a pair of probes in electrical contact with the ground surface;   generating (i) a current signal indicative of a current in the buried conductor based on the detected magnetic field and (ii) a voltage signal indicative of the measured voltage; and   simultaneously displaying the current and voltage signals at a user interface.