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Title:
REDUCING INDUCED VOLTAGES AND CURRENTS IN PIPELINES
Document Type and Number:
WIPO Patent Application WO/2018/157224
Kind Code:
A1
Abstract:
A method for reducing induced voltages in a pipeline involves measuring at least one of a node voltage and electric current between a node, on a first conduction path extending from a point on the pipeline to an output of a controlled current source, and a voltage reference point not on the pipeline itself. A controlled current source has an output that injects an injection current into the node such that the node voltage or the electric current meets at least one criterion.

Inventors:
XU WILSUN (CA)
Application Number:
CA2017/000040
Publication Date:
September 07, 2018
Filing Date:
March 02, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
XU WILSUN (CA)
International Classes:
F17D5/08; G01R19/00
Foreign References:
US5541459A1996-07-30
US7317321B22008-01-08
JP4837703B22011-12-14
JP5270470B22013-08-21
JPH09292100A1997-11-11
Attorney, Agent or Firm:
KNOX, John, W. et al. (CA)
Download PDF:
Claims:
EMBODIMENTS IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of reducing induced voltages in a pipeline, the method comprising: measuring at least one of a node voltage and an electric current between: a node, on a conduction path extending from a point on the pipeline to an output of a controlled current source; and a voltage reference point not on the pipeline; and controlling the controlled current source to cause the output to inject an injection current into the node such that the at least one of the node voltage and the electric current meets at least one criterion.

2. The method of claim 1 wherein the at least one criterion comprises the at least one of the node voltage or the electric current being lesser than, greater than, or equal to a pre-defined value.

3. The method of claim 1 or 2 wherein controlling the controlled current source comprises causing the injection current to increase or decrease when the at least one of the node voltage and the electric current does not meet the at least one criterion.

4. The method of any one of claims 1 to 3 wherein the node is closer to the controlled current source than the pipeline and the method further comprises: producing a measurement signal in response to the at least one of the node voltage and the electric current; and controlling the injection current in response to the measurement signal.

5. The method of any one of claims 1 to 3 wherein the node is closer to the pipeline than the controlled current source and the method further comprises: producing a measurement signal representing the at least one of the node voltage and the electric current; and controlling the injection current in response to the measurement signal.

6. The method of claim 4 or 5 wherein: producing the measurement signal comprises: sampling a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency; and producing a control signal in response to the sampled waveform; and controlling the injection current comprises controlling the injection current in response to the control signal.

7. The method of claim 6 wherein the sampling the waveform comprises sampling the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

8. The method of any one of claims 1 to 7 further comprising superposing the injection current on a common mode current.

9. The method of claim 8 wherein superposing the injection current comprises superposing the injection current on a direct current.

10. The method of claim 8 or 9 wherein the common mode current is associated with an impressed current cathodic protection (ICCP) system associated with the pipeline.

11. The method of claim 10 wherein measuring the at least one of the node voltage and the electric current comprises measuring the node voltage and wherein the method further comprises: measuring a protection voltage between: the node; and an anode of the ICCP system; and producing a second measurement signal in response to the protection voltage.

12. The method of claim 11 further comprising producing the common mode current.

13. The method of claim 12 wherein producing the common mode current comprises controlling an output of a DC/DC converter in response to the second measurement signal.

14. The method of any one of claims 4 to 7 wherein controlling the injection current comprises causing a switching mode power supply to supply the injection current to the node.

15. The method of any one of claims 4 to 7 wherein controlling the injection current comprises causing a power amplifier to supply the injection current to the node.

16. A method of reducing power line induced voltages in a pipeline, the method comprising executing the method of any one of claims 1 to 15 at each of a plurality of nodes on respective conductive paths from respective points on the pipeline, the respective points on the pipeline corresponding to respective changes in spacing between portions of the pipeline and a power line.

17. The method of claim 16 further comprising independently executing the method of any one of claims 1 to 15 at the each of the plurality of nodes.

18. An apparatus for reducing induced voltages in a pipeline, the apparatus comprising: means for measuring at least one of a node voltage and an electric current between: a node, on a conduction path extending from a point on the pipeline to an output of a controlled current source; and a voltage reference point not on the pipeline; and means for controlling the controlled current source to cause the output to inject an injection current into the node such that the at least one of the node voltage and the electric current meets at least one criterion.

19. The apparatus of claim 18 wherein the at least one criterion comprises the at least one of the node voltage and the electric current being lesser than, greater than, or equal to a pre-defined value.

20. The apparatus of claim 18 or 19 wherein means for controlling the controlled current source comprises means for causing the injection current to increase or decrease when the at least one of node voltage and the electric current does not meet the at least one criterion.

21. The apparatus of any one of claims 18 to 20 wherein: the node is closer to the controlled current source than the pipeline; the means for measuring comprises means for producing a measurement signal in response to the at least one of the node voltage and the electric current; and the means for controlling the controlled current source controls the injection current in response to the measurement signal.

22. The apparatus of any one of claims 18 to 20 wherein: the node is closer to the pipeline than the controlled current source; and the means for measuring comprises means for producing a measurement signal in response to the at least one of the node voltage and the electric current; and the means for controlling the controlled current source controls the injection current in response to the measurement signal.

23. The apparatus of claim 21 or 22 wherein: the means for producing the measurement signal comprises: means for sampling a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency; and means for producing a control signal in response to the sampled waveform; and the means for controlling the controlled current source controls the injection current in response to the control signal.

24. The apparatus of claim 23 wherein the means for sampling the waveform samples the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

25. The apparatus of any one of claims 18 to 24 further comprising means for superposing the injection current on a common mode current.

26. The apparatus of claim 25, wherein the common mode current comprises a direct current.

27. The apparatus of claim 25 or 26, wherein the common mode current is associated with an impressed current cathodic protection (ICCP) system associated with the pipeline.

28. The apparatus of claim 27 wherein: the means for measuring measures the node voltage; the apparatus is configured to be coupled to: the ICCP system, wherein the ICCP system comprises an anode; and the apparatus comprises: means for measuring a protection voltage between the node and the anode, and means for producing a second measurement signal in response to the protection voltage.

29. The apparatus of claim 28 further comprising means for producing the common mode current.

30. The apparatus of claim 29 wherein the means for producing the common mode current comprises means for controlling an output of a DC/DC converter in response to the second measurement signal.

31. The apparatus of any one of claims 18 to 30 wherein the means for controlling the controlled current source comprises means for controlling a switching mode power supply.

32. The apparatus of any one of claims 18 to 30 wherein the means for controlling the controlled current source comprises means for controlling a power amplifier.

33. A system for reducing power line induced voltages in a pipeline, the system comprising: a plurality of the apparatuses of any one of claims 18 to 32 connected to respective nodes of a plurality of nodes on respective electrical conductive paths from respective points on the pipeline, the respective points on the pipeline corresponding to respective changes in spacing between portions of the pipeline and a power line.

34. The system of claim 33 wherein each apparatus of the plurality of apparatuses operates independently of any other apparatus of the plurality of apparatuses, at each of the plurality of nodes.

35. An apparatus for reducing induced voltages in a pipeline, the apparatus comprising: a measurement device configured to measure at least one of a node voltage and an electric current between: a node, on a conduction path extending between a point on the pipeline and an output of a controlled current source; and a voltage reference point not on the pipeline; and the controlled current source, wherein the controlled current source is configured to inject an injection current into the node to cause the at least one of the node voltage and the electric current to meet at least one criterion.

36. The apparatus of claim 35 wherein the at least one criterion comprises the at least one of the node voltage and the electric current being lesser than, greater than, or equal to a pre-defined value.

37. The apparatus of claim 35 or 36 wherein the controlled current source is further configured to cause the injection current to increase or decrease when the at least one of the node voltage and the electric current does not meet the at least one criterion.

38. The apparatus of any one of claims 35 to 37 wherein: the node is closer to the controlled current source than the pipeline; the measurement device is further configured to produce a measurement signal representing the at least one of the node voltage and the electric current; and the controlled current source is further configured to control the injection current in response to the measurement signal.

39. The apparatus of any one of claims 35 to 37 wherein: the node is closer to the pipeline than the controlled current source; and the measurement device is configured to produce a measurement signal representing the at least one of the node voltage and the electric current; and the controlled current source is configured to control the injection current in response to the measurement signal.

40. The apparatus of claim 38 or 39 wherein: the measurement device further comprises a sampling component configured to: sample a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency; and produce a control signal in response to the sampled waveform; and the controlled current source is configured to control the injection current in response to the control signal.

41. The apparatus of claim 40 wherein the sampling component samples the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

42. The apparatus of any one of claims 35 to 41 , wherein the controlled current source is configured to superpose the injection current on a common mode current.

43. The apparatus of claim 42, wherein the common mode current comprises a direct current.

44. The apparatus of claim 42 or 43, wherein: the apparatus is coupled to an impressed current cathodic protection (ICCP) system associated with the pipeline; and the common mode current is associated with the ICCP system.

45. The apparatus of claim 44 wherein the measurement device measures the node voltage, the ICCP system comprises an anode, and wherein the apparatus further includes: a protection voltage measuring device configured to: measure a protection voltage between the node and the anode; and produce a second measurement signal in response to the protection voltage.

46. The apparatus of claim 45, wherein the ICCP system is further configured to produce the common mode current.

47. The apparatus of claim 46 wherein the ICCP system further comprises a DC/DC converter and the ICCP system is configured to produce the common mode current by controlling an output of the DC/DC converter in response to the second measurement signal.

48. The apparatus of any one of claims 35 to 47 wherein the controlled current source includes a switching mode power supply.

49. The apparatus of any one of claims 35 to 47 wherein the controlled current source includes a power amplifier.

50. A system for reducing power line induced voltages in a pipeline, the system comprising: a plurality of apparatuses of any one of claims 35 to 49 connected to respective nodes of a plurality of nodes on respective electrical conductive paths from respective points on the pipeline, the respective points on the pipeline corresponding to respective changes in spacing between portions of the pipeline and a power line. The system of claim 50 wherein each apparatus of the plurality of apparatuses operates independently of any other apparatus of the plurality of apparatuses, at each of the plurality of nodes.

Description:
REDUCING INDUCED VOLTAGES AND CURRENTS IN PIPELINES BACKGROUND

1. Field

This disclosure relates to reducing corrosion in pipelines and more particularly to reducing induced voltages and currents in pipelines due to nearby overhead power lines.

2. Description of Related Art

When a metallic pipe of a pipeline is buried underground close to an overhead power line, a voltage may be electromagnetically induced in the longitudinal direction of the metallic pipe as a result of electric current flowing in the overhead power line. The induced voltage can cause an induced electric current in the metallic pipe if an electric circuit is available. Although a metallic pipe of a pipeline is normally coated with an electrically insulating any anti-corrosive coating, the coating can become breached due to cracks or pinholes, improper adhesion of the coating or other defects that create discontinuities in the coating. Such defects are called "holidays" in the coating. For example, rocks and other debris may damage the coating as the metallic pipe is installed underground. The difference in electric potential of the metallic pipe relative to the surrounding soil can cause an induced current to flow from the metallic pipe to the surrounding soil through the holiday, which can cause both electrolytic corrosion of the metallic pipe and potentially dangerous rises in the electric potential of the surrounding soil.

Pipeline corrosion caused by power line currents has been a concern to both pipeline and power industries for years. For example, inductive coordination standards have been established to govern the separation distance between power lines and pipelines [Canadian Standards Association C22.3 No.6-13 "Principles and Practices of Electrical Coordination Between Pipelines and Electric Supply Lines"]. Techniques exist for reducing the effect of voltage induction in pipelines. For example, United States patent no. 6,866,770 discloses that wires can be connected to a metallic pipe of a pipeline at regular intervals and can be buried in soil adjacent to the pipeline. This arrangement grounds the metallic pipe continuously and reduces the electrical potential difference between the metallic pipe and the surrounding soil. Further, United States patent no. 5,541 ,459 discloses coupling a portion of a pipeline to a transformer. The transformer is energized to produce an electromagnetic field to counter the induced voltage in the pipeline. Alternatively, United States patent no. 5,574,317 discloses coupling a compensating device to feed points on the pipeline. The compensating device injects an alternating voltage at the feed points to induce an alternating current to counter the induced voltage in the pipeline. However, these techniques can be complicated and costly as they require installing multiple devices at regular intervals on a pipeline and further require determining both magnitude and phase of the correction voltage to be applied.

Further, waveforms of power line currents have become increasingly non-sinusoidal due to the widespread use of non-linear energy use devices such as power electronics-based motor drives. An electrical current having a non-sinusoidal waveform may include both a fundamental frequency component and a set of harmonic frequency components which are integer multiples of the fundamental frequency component. For example, a non-sinusoidal current of a power line having a fundamental frequency at 60Hz may have a complex waveform formed from the combination of a fundamental frequency component at 60Hz, a first harmonic frequency component at 180Hz (3 rd harmonic), a second harmonic frequency component at 300HZ (5 th harmonic) and so on.

Harmonic frequency components of the current generally have much higher frequencies than the fundamental frequency component and can further cause imbalance among phases of a typical 3-phase alternating power line. These harmonic frequency components can, therefore, be quite potent in inducing voltages in pipelines. For example, a 3 rd harmonic component in a current in a 130kV line can produce an induced voltage that is as high as that produced by a fundamental frequency current.

SUMMARY

In one embodiment, there is provided a method of reducing induced voltages in a pipeline. The method involves measuring at least one of a node voltage and an electric current between: a node, on a conduction path extending from a point on the pipeline to an output of a controlled current source; and a voltage reference point not on the pipeline. The method further involves controlling the controlled current source to cause the output to inject an injection current into the node such that the at least one of the node voltage and the electric current meets at least one criterion.

The at least one criterion may involve the at least one of the node voltage or the electric current being lesser than, greater than, or equal to a pre-defined value.

Controlling the controlled current source may involve causing the injection current to increase or decrease when the at least one of the node voltage and the electric current does not meet the at least one criterion.

The node may be closer to the controlled current source than the pipeline and the method may further involve: producing a measurement signal in response to the at least one of the node voltage and the electric current; and controlling the injection current in response to the measurement signal.

The node may be closer to the pipeline than the controlled current source and the method may further involve: producing a measurement signal representing the at least one of the node voltage and the electric current; and controlling the injection current in response to the measurement signal. Producing the measurement signal may involve sampling a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency and producing a control signal in response to the sampled waveform. Controlling the injection current may involve controlling the injection current in response to the control signal.

Sampling the waveform may involve sampling the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

The method may further involve superposing the injection current on a common mode current.

Superposing the injection current may involve superposing the injection current on a direct current.

The common mode current may be associated with an impressed current cathodic protection (ICCP) system associated with the pipeline. Measuring the at least one of the node voltage and the electric current may involve measuring the node voltage. The method may further involve: measuring a protection voltage between the node and an anode of the ICCP system; and producing a second measurement signal in response to the protection voltage.

The method may further involve producing the common mode current. Producing the common mode current may involve controlling an output of a DC/DC converter in response to the second measurement signal.

Controlling the injection current may involve causing a switching mode power supply to supply the injection current to the node.

Controlling the injection current may involve causing a power amplifier to supply the injection current to the node. ln another embodiment, there is provided a method of reducing power line induced voltages in a pipeline. The method involves executing any one of the methods described above at each of a plurality of nodes on respective conductive paths from respective points on the pipeline. The respective points on the pipeline correspond to respective changes in spacing between portions of the pipeline and a power line.

The method may further involve independently executing any one of the methods described above at the each of the plurality of nodes.

In another embodiment, there is provided an apparatus for reducing induced voltages in a pipeline. The apparatus includes means for measuring at least one of a node voltage and an electric current between: a node, on a conduction path extending from a point on the pipeline to an output of a controlled current source; and a voltage reference point not on the pipeline. The apparatus further includes means for controlling the controlled current source to cause the output to inject an injection current into the node such that the at least one of the node voltage and the electric current meets at least one criterion.

The at least one criterion may include the at least one of the node voltage and the electric current being lesser than, greater than, or equal to a pre-defined value.

The means for controlling the controlled current source may include means for causing the injection current to increase or decrease when the at least one of node voltage and the electric current does not meet the at least one criterion.

The node may be closer to the controlled current source than the pipeline. The means for measuring may include means for producing a measurement signal in response to the at least one of the node voltage and the electric current. The means for controlling the controlled current source may control the injection current in response to the measurement signal.

The node may be closer to the pipeline than the controlled current source. The means for measuring may include means for producing a measurement signal in response to the at least one of the node voltage and the electric current. The means for controlling the controlled current source may control the injection current in response to the measurement signal.

The means for producing the measurement signal may include means for sampling a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency and means for producing a control signal in response to the sampled waveform. The means for controlling the controlled current source may control the injection current in response to the control signal. The means for sampling the waveform may sample the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

The apparatus may further include means for superposing the injection current on a common mode current. The common mode current may be a direct current.

The common mode current may be associated with an impressed current cathodic protection (ICCP) system associated with the pipeline.

The means for measuring may measure the node voltage. The apparatus may be configured to be coupled to the ICCP system. The ICCP system may include an anode. The apparatus may include means for measuring a protection voltage between the node and the anode and means for producing a second measurement signal in response to the protection voltage.

The apparatus may further include means for producing the common mode current.

The means for producing the common mode current may include means for controlling an output of a DC/DC converter in response to the second measurement signal. The means for controlling the controlled current source may include means for controlling a switching mode power supply.

The means for controlling the controlled current source may include means for controlling a power amplifier. In another embodiment, there is provided a system for reducing power line induced voltages in a pipeline. The system includes a plurality of any one of the apparatuses described above connected to respective nodes of a plurality of nodes on respective electrical conductive paths from respective points on the pipeline. The respective points on the pipeline correspond to respective changes in spacing between portions of the pipeline and a power line.

Each apparatus of the plurality of apparatuses may operate independently of any other apparatus of the plurality of apparatuses, at each of the plurality of nodes.

In another embodiment, there is provided an apparatus for reducing induced voltages in a pipeline. The apparatus includes a measurement device configured to measure at least one of a node voltage and an electric current between: a node, on a conduction path extending between a point on the pipeline and an output of a controlled current source; and a voltage reference point not on the pipeline. The apparatus further includes the controlled current source. The controlled current source is configured to inject an injection current into the node to cause the at least one of the node voltage and the electric current to meet at least one criterion.

The at least one criterion may include the at least one of the node voltage and the electric current being lesser than, greater than, or equal to a pre-defined value.

The controlled current source may be further configured to cause the injection current to increase or decrease when the at least one of the node voltage and the electric current does not meet the at least one criterion. The node may be closer to the controlled current source than the pipeline. The measurement device may be further configured to produce a measurement signal representing the at least one of the node voltage and the electric current. The controlled current source may be further configured to control the injection current in response to the measurement signal.

The node may be closer to the pipeline than the controlled current source. The measurement device may be configured to produce a measurement signal representing the at least one of the node voltage and the electric current. The controlled current source may be configured to control the injection current in response to the measurement signal.

The measurement device may further include a sampling component configured to sample a waveform of the measurement signal at a frequency sufficient to capture at least an alternating current component at a power line fundamental frequency and produce a control signal in response to the sampled waveform. The controlled current source may be configured to control the injection current in response to the control signal.

The sampling component may sample the waveform at a frequency sufficient to capture at least one harmonic component of the power line fundamental frequency.

The controlled current source may be configured to superpose the injection current on a common mode current.

The common mode current may include a direct current.

The apparatus may be coupled to an impressed current cathodic protection (ICCP) system associated with the pipeline. The common mode current may be associated with the ICCP system. The measurement device may measure the node voltage. The ICCP system may include an anode. The apparatus may further include a protection voltage measuring device configured to measure a protection voltage between the node and the anode and produce a second measurement signal in response to the protection voltage.

The ICCP system may be further configured to produce the common mode current. The ICCP system may further include a DC/DC converter and the ICCP system may be configured to produce the common mode current by controlling an output of the DC/DC converter in response to the second measurement signal.

The controlled current source may include a switching mode power supply.

The controlled current source may include a power amplifier. In another embodiment, there is provided a system for reducing power line induced voltages in a pipeline. The system includes a plurality of any one of the apparatuses described above connected to respective nodes of a plurality of nodes on respective electrical conductive paths from respective points on the pipeline. The respective points on the pipeline correspond to respective changes in spacing between portions of the pipeline and a power line.

Each apparatus of the plurality of apparatuses may operate independently of any other apparatus of the plurality of apparatuses, at each of the plurality of nodes. Other aspects and features of the embodiments described here will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the disclosure in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments,

Figure 1 is a plan view of a system comprising a pipeline in the vicinity of an overhead power line in accordance with one embodiment. Figure 2 is a broken perspective view of the pipeline of Figure 1 buried underground and in the vicinity of the overhead power line of Figure 1 installed above ground.

Figure 3A is a plan view of a configuration of a pipeline in the vicinity of an overhead power line in accordance with another embodiment. Figure 3B is a graph of voltage relative to ground at points along the pipeline shown in Figure 3A.

Figure 4A is a schematic representation of a voltage equivalent circuit of the pipeline shown in Figure 3A.

Figure 4B is a schematic representation of a current equivalent circuit of the pipeline shown in Figure 3A.

Figure 5 is a schematic representation of an apparatus for reducing power line induced electromagnetic forces (emfs) in the pipeline of Figure 3A in accordance with a first embodiment.

Figure 6 is a schematic representation of a controller and a controlled current source of the apparatus shown in Figure 5.

Figure 7 is a schematic representation of an apparatus for reducing power line induced emfs in the pipeline of Figure 3A in accordance with a second embodiment. Figure 8 is a schematic representation of a controller, a controlled current source and an impressed current cathodic protection (ICCP) system of the apparatus shown in Figure 7.

Figure 9 is a schematic representation of an apparatus for reducing power line induced emfs in the pipeline of Figure 3 in accordance with a third embodiment.

DETAILED DESCRIPTION

Referring to Figure 1 , a plan view of an overhead power line is shown generally at 10. The overhead power line 10 may be a 3-phase alternating current power line, for example. In the embodiment shown, the overhead power line 10 has a first segment 12, a second segment 14, a third segment 16 and a fourth segment 18 and includes a first directional change 20 at a transition between the first and second segments 12, 14, a second directional change 22 at a transition between the second and third segments 14, 16 and a third directional change at a transition between the third and fourth segments 16, 18. In other embodiments, the power line 10 may have greater or fewer segments and directional changes.

The overhead power line 10 is disposed near a pipeline, such as an oil pipeline shown generally at 30, buried underground in the vicinity of the overhead power line 10.

The pipeline 30 has a first segment 32, a second segment 34 and a third segment 36 and includes a first directional change 38 at a transition between the first and second segments 32, 34 and a second directional change at a transition between the second and third segments 34, 36. In other embodiments, the pipeline 30 may have greater or fewer segments and directional changes.

In the embodiment shown in Figure 1 , a first portion 50 of the first pipeline segment 32 is parallel to a portion 52 of the first power line segment 12 and is located a first distance from the portion 52. A horizontal component 54 of the first distance is depicted in Figure 1. The first distance also has a vertical component (not shown), as the power line 10 is above ground while the pipeline 30 is below ground and are thus are not in the same horizontal plane. A second portion 56 of the first pipeline segment 32 is parallel to a portion 58 of the third power line segment 16 and is located at a second distance from the portion 58. A horizontal component 55 of the second distance is depicted in Figure 1 , and the second distance may also include a vertical component (not shown). The second pipeline segment 34 of the pipeline 30 is not parallel to any segment of the power line 10 and a first portion 60 of the third pipeline segment 36 is parallel to a second portion 62 of the third power line segment 16.

In embodiments where the power line 10 carries the 3-phase alternating electrical current, a constant changing of direction of the AC in the power line 10 causes an electromagnetic field (EM field) surrounding the power line 10 to constantly change, such as constantly contract and expand for example. This changing EM field can induce electromagnetic forces (emfs) and/or voltages in the pipeline 30, which can, for example, induce a voltage profile along the pipeline 30 and cause a current to flow from the pipeline 30 to the surrounding soil to form an electric circuit.

A strength of the induced emf at any point in the pipeline 30 is dependent on factors such as a magnitude of the AC current carried by the power line 10, a distance between the power line 10 and the point on the pipeline 30 and an orientation of the pipeline 30 relative to the power line 10. For example, the portions 50, 56, and 60 of the pipeline 30 that are parallel to, respectively, portions 52, 58 and 62 of the power line 10 may experience stronger induced emf than portions of the pipeline 30 not parallel to the power line 10. Additionally, the portion 50 of the pipeline 30, which is close to portion 52 of the power line 10, may experience a stronger induced emfs than the portion 56 of the pipeline 30, which is further away from the power line 10.

Further, any geometric discontinuities in either the pipeline 30 or the power line 10 relative to each other, such as changes in parallelism between the pipeline 30 and the power line 10, can cause an abrupt directional change of the EM field experienced by the pipeline 30, which can affect the induced emfs in the pipeline 30. Accordingly, points on the pipeline 30 corresponding to the first and third directional changes 20, 24 of the power line 10 and the first and second directional changes 38, 40 of the pipeline 30 may experience stronger induced emfs than other portions of the pipeline 30.

A voltage profile representing voltage magnitude along the pipeline 30 due to the emfs induced by the power line 10 at various points along the pipeline 30, at a particular instant in time, is shown generally at 70 in Figure 1. It can be seen that peaks in a strength of the voltage profile occur at points on the pipeline 30 corresponding to the changes in parallelism between the pipeline 30 and the power line 10 as noted above. For example, in the embodiment shown, the voltage profile 70 includes: a first peak 72 at a point 74 on the pipeline 30 corresponding to the first directional change 20 of the power line 10, a second peak 76 at a point 78 on the pipeline 30 corresponding to the first directional change 38 of the pipeline 30; a third peak 80 at a point 82 on the pipeline 30 corresponding to the second directional change 40 of the pipeline 30; and a fourth peak 84 at a point 86 on the pipeline 30 corresponding to the third directional change 24 of the power line 10.

The various embodiments described herein may facilitate the creation of a desirable voltage profile in a pipeline by injecting current into points, such as points 74, 78, 82 and 86 on the pipeline 30, corresponding to peaks in the voltage profile for a particular pipeline, such as peaks 72, 76, 80 and 84 of the voltage profile 70 of the pipeline 30. These injected currents can attenuate the voltage at the peaks to produce a resultant voltage profile at least without peaks of the same magnitude as would occur without the injected currents. Further, these injected currents can also generally attenuate the voltage profile to produce a resultant voltage profile with reduced voltage at all points along the pipeline.

Referring to Figure 2, a portion of the pipeline 30 is shown at 90. The portion 90 of the pipeline 30 is comprised of a longitudinally extending metallic pipe 92 having an outer surface 94 with a coating 96 covering the entire outer surface 94. The coating 96 may be electrically insulating and may provide corrosion protection. A portion of the power line 10 is also shown in Figure 2 and the current flowing in the portion of the power line 10 induces longitudinal emfs 102 at various points along the portion 90 of the pipeline 30.

The coating 96 may substantially electrically insulate the metallic pipe 92 from surrounding soil 91 in which the metallic pipe 92 is buried. However, the coating 96 can become damaged due to scratches or other discontinuities such as may occur during installation of the pipeline 30, for example. Such discontinuities are called "holidays", for example. A holiday 97 in the coating 96 may expose a portion of the outer surface 94 of the metallic pipe 92, such as exposed pipe portion 98 for example, to the environment. Direct contact of the exposed pipe portion 98 with the surrounding soil 91 , moisture in the surrounding soil 91 or electrolytic liquid in the surrounding soil 91 can provide a conduction path for any induced current to flow to or from the exposed pipe portion 98.

For example, an electric current can flow from the metallic pipe 92 at the exposed pipe portion 98 into the surrounding soil 91 , through the surrounding soil 91 , and from the surrounding soil 91 back into the metallic pipe 92 at another exposed pipe portion 100 of the metallic pipe 92 some distance away from the first exposed pipe portion 98 or at another exposed pipe portion (not shown) in another portion of the pipeline 30 electrically and mechanically coupled to the exposed pipe portion 98. Thus, the metallic pipe 92 between the exposed pipe portions 98 and 100 and the adjacent soil form an electrical circuit 101 having voltage sources provided by the induced emfs along the metallic pipe 92. This electrical circuit 101 can experience sufficient electric current, shown generally as I, caused by the difference in voltage between exposed pipe portions 98 and 100 for example, to cause significant electrolytic corrosion of the outer surface 94 at the exposed pipe portions 98 and/or 100. Referring now to Figure 3A, a simple pipeline and power line configuration is shown generally at 120. In the configuration 120, a power line shown generally at 122 is disposed proximate to a nearby pipeline shown generally at 126.

The power line 122 has a first segment 124, a second segment 128 and a third segment 130, and has a first directional change 151 at a transition between the first and second segments 124, 128 and a second directional change 153 at a transition between the first and third segments 124, 130. The first segment 124 is parallel to the pipeline 126 while the second and third segments 128, 130 are non-parallel to the pipeline 126.

The pipeline 126 is linear and includes metallic pipe 160 (shown in Figures 5, 7 and 8) having a metallic outer surface 162 (shown in Figures 5, 7 and 8) covered by a coating 127. The coating 127 may protect the metallic outer surface 162 from corrosion and may further electrically insulate the metallic pipe 160. In the embodiment shown in Figure 3A, the coating 127 includes a first holiday 131 and a second holiday 133 through which portions of the metallic outer surface (162) are exposed. In other embodiments, the coating 127 may include additional holidays. A parallel zone portion 129 of the pipeline 126 is parallel to the power line 122, and both the first and second holidays 131 , 133 are disposed within the parallel zone portion 129.

A current flowing through the power line 122 induces longitudinal emfs in the pipeline 126, and a resulting voltage profile at various points along the pipeline 126 relative to the surrounding soil, at a particular point in time, is shown generally at 132 in Figure 3B. For the reasons noted above, peaks 135 and 137 in the voltage profile 132 occur at points 150 and 152 respectively on the pipeline 126 corresponding to, respectively, the first and second directional changes 151 and 153 of the power line 122 and opposite ends of the parallel zone portion 129 of the pipeline 126.

Referring now to Figure 4A, a voltage equivalent circuit for the configuration (120 in Figure 3A) is shown generally at 110. This voltage equivalent circuit 110 may be used to explain a magnitude of the voltage profile at various points on the pipeline 126. Specifically, the current of the power line 122, shown generally as IF, induces longitudinal emfs, shown general as e n , at various locations along the metallic pipe 160 that forms the pipeline 126. These induced emfs result in a potential difference, shown generally as Vpotentiai, across resistances a) along a length of the pipeline 126, shown generally as series impedances Z nn , and b) between the pipeline 126 and the soil surrounding the pipeline, shown generally as shunt impedances R gn . The voltage equivalent circuit 110 thus includes a plurality of series impedances Z nn and shunt impedances R gn connected in a ladder arrangement.

The series impedances Z nn are complex and represent the impedance presented to direct current (DC) and AC components of the induced longitudinal emfs flowing in the pipeline along the length of the pipeline 126. The series impedances Z nn are proportional to factors such as the resistivity of the metal material of the metallic pipe (160), for example. The shunt impedances R gn are also complex and represent the impedance presented to DC and AC components of the induced longitudinal emfs flowing in the pipeline 126 between the pipeline 126 and the surrounding soil. The shunt impedances R gn may be proportional to the resistivity of the coating of the pipeline 126 and the substance transported by the pipeline 126, for example, and other factors such as existence of holidays in the coating 127 or the thickness of the coating 127 if there are no holidays in the coating 127.

As neither the series impedances Z nn nor the shunt impedances R gn presented along the pipeline 126 are infinite, the induced emfs in the parallel zone portion 129 of the pipeline (126) by the power line (122) may produce a current flow in the pipeline 126. Accordingly, the voltage equivalent circuit shown in Figure 4A may be expressed in a current sense, by a current equivalent circuit 111 shown in Figure 4B. Due to the high induced emfs at points 150 and 152 of the pipeline 126, a significant current may be induced at these points, represented as first and second equivalent current sources l s i and l S 2 at the points 150 and 152 located on opposite ends of the parallel zone portion 129 (shown in Figure 4).

Either the voltage equivalent circuit 110 or the current induced circuit 111 , and hence the pipeline 126, may have the voltage profile as shown in Figure 3B at 132, at a particular point in time.

The methods described herein, in certain embodiments, counteract the first and second equivalent current sources l s i and l S 2 shown in Figure 4B with injection currents nji and li n j 2 at points 150 and 152 on the pipeline 126 so that the effects of the first and second current sources l s i, l S 2 caused by the induced emfs are reduced or negated.

For example and referring now to Figure 3A, 3B and 4B, by injecting the injection currents lj n ji and I in j2 at, respectively, point 150 and point 152 on the pipeline 126, the peaks 135 and 137 of the voltage profile 132 may be reduced or negated to produce a new resultant longitudinal voltage profile 138 which is shown as a flat zero-voltage profile in Figure 3B. The reduced voltages at points 150 and 152 along the pipeline 126 may thus both attenuate the peaks 135 and 137 of the voltage profile 132 and reduce the net voltage profile in the parallel zone portion 129 overall, thus reducing the effects of the first and second equivalent current sources l s i, l S 2 in the current equivalent circuit 111 . The reduction in current flowing to/from the pipeline 126 results in a reduction of corrosion of the pipeline 126 and may further reduce potentially dangerous rises in the V po tentiai of the surrounding soil.

In accordance with the teachings herein, there is provided a method for reducing induced voltages in a pipeline, by measuring at least one of a node voltage and electric current between a node, on a conduction path extending from a point on the pipeline to an output of a controlled current source and a voltage reference point not on the pipeline itself. The method further involves controlling a controlled current source to cause the output thereof to inject an injection current into the node such that the node voltage or the electric current meets at least one criterion.

The method may be performed at one point on the pipeline or at many points on the pipeline. The method performed at each point may be executed independently of the method performed at each other point on the pipeline or the method performed at each point may be performed in a coordinated way with the method performed at one or more other points to produce a desired voltage profile in the pipeline.

Various ways of implementing the above method are described below.

First Embodiment

Referring to Figure 5, a first embodiment of an apparatus for reducing induced voltages and currents in a pipeline, such as the pipeline 126 for example, is shown generally at 180. In the embodiment shown, the apparatus 180 includes a controlled current source 190 having an output 192. The apparatus 180 further includes a controller 194, an apparatus ground 196 and a measurement device 198. The controlled current source 190 is configured to produce an injection current linj, which may function as either the li n ji or the l m \2 (shown in Figure 4B) for example, at the output 192 in response to a measurement of voltage or current at a node 200 on a conduction path 182, as will be described in greater detail below.

A point 168 on the metallic pipe 160 of the pipeline 126 is coupled to the output 192 of the controlled current source 190 via the conduction path 182. The point 168 is generally a physical location on the pipeline 126 which corresponds to a change in parallelism between the pipeline 126 and the power line 122. For example, the point 168 may be either of the points 150 or 152 shown in Figure 3 on opposite ends of the parallel zone portion 129 of the pipeline 126 and corresponding to, respectively, the first or second directional changes 151 , 153 the power line 122. In other embodiments, the point 168 may be any one of the points 78, 82 on pipeline 30 shown in Figure 1 corresponding to first and second directional changes 38, 40 shown in Figure 1 in the pipeline 30 or points 74, 86 on the pipeline 30 corresponding to first and third directional changes 20, 24 shown in Figure 1 of the power line 10.

The conduction path 182 is, generally, a low impedance conduction path such as may be provided by a stranded wire. An 8-guage stranded wire may be suitable as the conduction path 182, for example. The wire may be mechanically and electrically secured to the point 168 on the metallic pipe 160, such as by a screw, soldering, brazing or by any other suitable method of mechanically and electrically connecting a conductive wire to a metallic pipe.

The measurement device 198 is coupled to the node 200 on the conduction path 182 and measures at least one of a node voltage and an electric current between a) the node 200 on the conduction path 182 and b) a voltage reference point 202 separate from the pipeline 126 and not on the pipeline. The voltage reference point 202 may be supplied by the apparatus ground 196, for example. The measurement device 198 then produces a measurement signal representing the measured node voltage at the node 200 or the measured electric current into or out of the node 200 to the voltage reference point 202. The measurement signal may then be transmitted by the measurement device 198 for receipt by the controller 194.

In some embodiments, the measurement device 198 may be a voltage sensor, and may produce the measurement signal such that the measurement signal is in a suitable range, such as 0-10 volts for example. In some other embodiments, the measurement device 198 may produce the measurement signal as a waveform representing the node voltage or the electric current measured at node 200, such that the measurement signal is a voltage waveform or a current waveform, for example. Additionally, in some embodiments, the measurement device 198 may sample the node voltage or the electric current at a frequency high enough to capture components of the node voltage or the electric current which are caused by a fundamental frequency of the power line 122 or a harmonic component of the fundamental frequency of the power line 122. In one embodiment, the measurement device 198 samples the node voltage or the electric current at a speed sufficient to enable at least the 3 rd and 5 th harmonics of the fundamental frequency of the power line 122 to be represented by the measurement signal. The ability to capture additional harmonics of the fundamental frequency may be desirable where greater accuracy is required.

In the embodiment shown in Figure 5, the node 200 is located closer to the controlled current source 190 than the pipeline 126. However, in other embodiments, the node 200 can be anywhere along the conduction path 182 between the point 168 on the pipeline 126 and the output 192 of the controlled current source 190.

Additionally, in the embodiment shown in Figure 5, the voltage reference point 202 is effectively the apparatus ground 196. However, in other embodiments, the voltage reference point 202 may be a grounding point 195 in soil adjacent the pipeline 126, or at some remote location away from the pipeline 126. Generally, the voltage reference point 202 is a point in a circuit, such as the current equivalent circuit 111 shown in Figure 4B for example, through which induced current in the pipeline 126 flows. However, the voltage reference point 202 is not on the pipeline 126 itself.

The controller 194 receives the measurement signal from the measurement device 198 and produces a control signal to control the injection current l inj produced by the controlled current source 190 in response to the measurement signal. Referring now to Figure 6, the components of the controller 194 in accordance with one embodiment will be described in detail. In other embodiments, the controller 194 may include different or alternative components to control the injection current l, n j produced by the controlled current source in response to the measurement signal.

In the embodiment shown in Figure 6, the controller 194 includes an analog-to- digital (A/D) converter 212, a threshold value source 214, an error amplifier 216 and a microcontroller 218.

The A/D converter 212 includes a sampling component which performs a sampling function and samples the measurement signal from the measurement device 198 and produces a digital signal in response to the measurement signal for receipt by the error amplifier 216. For example, in embodiments where the measurement signal comprises a waveform, the sampling component may sample the waveform of the measurement signal at a frequency such that, the digital signal produced by the A/D converter 212 represents instantaneous values of the waveform of the measurement signal at successive instances in time. In embodiments where it is important to counteract induced emfs caused by harmonic components of the fundamental frequency of the power line 122, the measurement device 198 and the A/D converter 212 both need to measure and sample, respectively, at frequencies fast enough to capture and sample the harmonic components noted above.

The error amplifier 216 compares the digital signal to a defined threshold value received from the threshold value source 214 and produces an error signal representing the difference between the digital signal and the defined threshold value for receipt by the microcontroller 218. The microcontroller 218 is configured to produce a control signal 219, in response to the error signal, and hence in response to the sampled waveform of the measurement signal, for controlling the controlled current source 190.

In the embodiment shown, the controlled current source 190 is a switching mode power supply and includes a power source 220, a power supply circuit 222, and a first DC/AC converter 223 comprising a pulse-width modulated (PWM) switching circuit 224, a PWM controller 226, and an output interface 228. ln the embodiment shown, the power supply circuit 222 in conjunction with the power source 220 acts is a stiff DC source for powering the PWM switching circuit 224.The PWM controller 226 is configured to produce switching control signals for controlling switches of the PWM switching circuit 224 in response to the control signal 219. The PWM controller 226 is configured to produce the switching control signals so that they have suitable phasing and duty cycles for controlling the PWM switching circuit 224 to cause an appropriate output current to flow though the output interface 228 to provide an appropriate injection current \- mi at the output 192 of the controlled current source 190 of the apparatus 180 in a range suitable to counteract the induced emfs in the pipeline 126 and to produce an attenuated voltage profile in the pipeline 126 (such as the flat zero-voltage profile 138 in Figure 3B, for example).

For example, the microcontroller 218 of the controller 194 may be programmed with Proportional, Integral and Derivative (PID) control algorithms to implement a control transfer function operating on and/or modulating the error signal to produce the control signal 219 to cause the PWM controller 226 to control the PWM switching circuit 224 to cause the ultimately produced injection current \ m \ to vary. For example, the error signal may be modulated or transformed by the microcontroller 218 to produce control signals, such as the control signal 219, which function to maintain the node voltage or the electric current measured at the node 200 (shown in Figure 5) at a criterion or at least one criterion. For example the at least one criterion might be that the node voltage measured at the node 200 is to be kept within +/- 0.1 volts of zero, that the difference between the current into the node 200 and the current out of the node 200 is at or within a few milliamps of zero, or a combination of both. Alternatively or in addition, the at least one criterion may be that the node voltage, the electric current, or a combination of both, is one of lesser than, greater than, or equal to a pre-defined value.

Alternatively, other configurations of the controlled current source 190 may be used, such as a voltage controlled power amplifier, for example, (not shown) wherein the control signal produced by the microcontroller 218 is a voltage signal for controlling an output current of a class A power amplifier, for example.

Referring still to Figure 6, in the embodiment shown, the output interface 228 includes a capacitive-inductive filter 240, which filters out voltage and current spikes resulting from the PWM switching circuit 224 and provides a smooth output current as the linj. The capacitive-inductive filter 240 may be a low-pass filter, for example. In embodiments of the apparatus 180 where emfs induced by harmonic components of a power line current are being countered with the injection current linj, the cutoff frequency of the capacitive inductive filter 240 needs to be high enough to enable the injection current Lj produced by the output 192 to have a frequency content at least as high as the fifth harmonic of the fundamental frequency of the power line 122 (such as 300Hz for a 60 Hz power line, for example).

Referring back to Figure 5, the controlled current source 190 is configured to inject a positive or negative injection current \ mi into the node 200, in response to the control signal 219, and hence in response to the measurement signal, such that the node voltage at the node 200 or the electric current into or out of the node 200 meets the above mentioned criterion or at least one criterion. Generally, the controller 194 may cause the injection current nj to increase or decrease when the node voltage or the electric current does not meet the at least one criteria.

Desirably, the controlled current source 190 injects sufficient positive or negative injection current linj into the node 200 to entirely counteract the induced current caused by the induced emfs in the pipeline 126 such that a net current in the pipeline 126 is attenuated to, or close to, zero. Due to the high conductivity and low impedance of the conduction path 182, a net current of zero in the pipeline 126 causes the node voltage measured by the measurement device 198 to be zero or causes the net flow of current into or out of the node 200 measured by the measurement device 198 to be zero, for example, and correspondingly, a "zero" measurement by the measurement device 198 at the node 200 indicates that the net flow of current into or out of the point 168 on the metallic pipe 160 is also zero. In certain embodiments, the controller 194 and the controlled current source 190 act in a feedback loop tending to try to maintain the measured node voltage at the node 200 in compliance within a desired criterion or at least one desired criterion , such as at or near zero or tending to try to keep the current into or out of the node

200 in compliance within the desired criterion or at least one desired criterion, such as at or near zero.

In embodiments where the injected current \- mi is required to counter emfs induced by harmonic components of a power line current, the measurement device 198, the controller 194 and the controlled current source 190 must have a fast enough response time to ensure that the node voltage or the electric current measured at the node 200, the measurement signal produced in response to the node voltage and the electric current, and the error signal produced in response to the measurement signal, has a frequency content at least as high as the third and fifth harmonic frequencies of the fundamental frequency of the power line 122.

In other embodiments, the apparatus 180 may include other auxiliary elements. For example, the apparatus 180 may include a data logging element for monitoring and recording values of the measured node voltage and/or the measured electric current, and/or the waveforms of the measurement signal. The apparatus 180 may further include a GPS element to add location information to the data logged by the data logging element, a clock element to add time information to the data logged by the data logging element, and/or a communication element to send status information to a remote location. The apparatus 180 may further include a protection unit, for example, to protect the apparatus 180 from overvoltage should the measured voltage or current exceed a threshold such as may occur due to lightning strikes to the power line or pipeline. Second Embodiment

Referring to now Figure 7, a second embodiment of an apparatus for reducing induced voltages and currents in a pipeline, such as the pipeline 126 for example, is shown at 250. The apparatus 250 is similar to the apparatus 180 shown in Figure 5 and includes the controlled current source 190 of Figures 5 and 6 having the output 192, a first controller substantially identical to the controller 194, the apparatus ground 196 and the measurement device 198. The point 168 on the metallic pipe 160 of the pipeline 126 is coupled to the output 192 of the controlled current source 190 via a conduction path 252 and the measurement device 198 measures at least one of a node voltage and an electric current between a node 270 on the conduction path 252 and a voltage reference point 272, which in this embodiment is at or near the apparatus ground 196.

However, unlike the apparatus 180 shown in Figure 5, the apparatus 250 shown in Figure 7 further includes an impressed current cathodic protection (ICCP) system shown generally at 280. The ICCP system 280 may be integrated into the apparatus 250 as shown, may be provided in the same housing as the apparatus 250, or may be a separate component.

In the embodiment shown, the ICCP system 280 includes a second controller 281 , an adjustable ICCP direct current (DC) power source 282, an ICCP conductor 284 and an anode 286 terminating at a distal end 285 of the ICCP conductor 284. The anode 286 is, when the ICCP system 280 is in operation, buried in the surrounding soil.

In normal operation, the ICCP DC power source 282 acts as a direct current source powering a cathodic protection circuit comprising the ICCP conductor 284, the anode 286, the soil between the anode 286 and an exposed portion 299 of the metallic pipe 160 (which may be exposed due to a holiday in the coating 127, for example), a portion of the metallic pipe 160, the conduction path 252 and the ICCP DC power source 282. The current provided by the ICCP DC power source 282 produces a common mode current in the cathodic protection circuit, which provides cathodic shielding to the metallic pipe 160 by forcing current from a reference output 253 of the ICCP DC power source 282, through the ICCP conductor 284, out of the anode 286, through the soil surrounding the pipeline, to the metallic pipe 1 60, through the conduction path 252, and back to the ICCP DC source 282 through a common connection wire 295. Correspondingly, a node voltage measured by the measurement device 198 between the node 270 and the voltage reference point 272 would include a DC voltage component associated with the common mode current produced by the ICCP DC power source 282. Further, the injection current linj produced by the controlled current source 1 90 through the conduction path 252 would be superposed on the common mode current flowing through the conduction path 252.

The ICCP system 280 further includes its own ICCP voltage sensor 290, which is configured to measure a protection voltage between the node 270 on the conduction path 252 and a point on the ICCP conductor 284.

Referring now to Figure 8, the components of the second controller 281 in accordance with one embodiment will be described in detail. In other embodiments, the second controller 281 may include different or alternative components for controlling the injection current linj in combination with the first controller 194 so that the node voltage and the electric current at the node 270 meets the at least one criterion in a manner that accounts for the common mode current produced by the ICCP DC power source 282.

In the embodiment shown in Figure 8, the second controller 281 includes a second analog to digital (A/D) converter 283, a second defined threshold source 287, a second error amplifier 291 and a second microcontroller 293. The second A/D converter 283 receives a voltage measurement signal from the ICCP voltage sensor 290 and produces a second digital signal for use by the second error amplifier 291. The second defined threshold source 287 produces a second threshold value signal for use by the second error amplifier 291 . The second error amplifier 291 compares the second digital signal and the second defined threshold value signal to produce a second error signal representing the difference between the second digital signal and the second defined threshold value signal for receipt by the second microcontroller 293. The second microcontroller 293 then produces a second control signal 296 for controlling the ICCP DC power source 282.

In the embodiment shown, the ICCP DC power source 282 includes a DC/DC converter 292 having an input 297 supplied by the power supply circuit 222 of the controlled current source 190. The DC/DC converter 292 also has first and second output terminals 298 and 294. The ICCP conductor 284 is connected to the DC/DC converter 292 at the first terminal 298. The controlled current source 190 is connected to the DC/DC converter 292 at the second terminal 294, for example, the output 192 of the controlled current source 190 may be connected to the second terminal 294 via the common connection wire 295. The injection current \ m \ produced by the controlled current source 190 is thus superposed on the common mode current produced by the ICCP DC power source 282 to produce the net injection current to be supplied to the point 168 on the pipeline 126 shown in Figure 7, for simultaneous cathodic protection of the pipeline 126 and reduction of a voltage profile in the pipeline 126.

In other embodiments, either microcontroller 218 or microcontroller 293 can be configured to perform the functions of both the microcontrollers 218 and 293 and/or a multiple channel A/D converter may be used to combine the functions of both A/D converters 212 and 283.

It will be appreciated that the error amplifiers 216 and 291 can be configured so that the output ranges of the error signals produced by the error amplifiers 216 and 291 can be set to suitable ranges for receipt by the respective microcontrollers 218 and 293. In addition, the microcontrollers 218 and 293 can be configured to implement suitable transfer functions that cause each respective microcontroller to produce the respective control signal (219 and 296) compatible with respective control inputs of the PWM controller 226 and the DC/DC converter 292 respectively and the switching circuit 224 and DC/DC converter 292 can be configured appropriately to provide output currents in ranges suitable for producing an injection current L j with sufficient AC current and sufficient harmonic components for reducing the voltage profile caused by induced emfs in the pipeline and for providing impressed current cathodic protection. Further, it will be appreciated that the voltage profile at any point in time in the pipeline caused by induced emfs in the pipeline may be determined empirically, for example. From these determined voltage profiles, magnitudes of injection currents required to be injected into the pipeline can be determined, from which the required range of injection current can be determined for any given location on the pipeline. The ranges for the DC current required to be produced by the ICCP DC source can be determined in the same way such ranges are determined for conventional ICCP systems.

Third Embodiment Referring to Figure 9, an apparatus for reducing induced voltages and currents in a pipeline, such as the pipeline 126 for example, according to a third embodiment is shown generally at 300.

The apparatus 300 is similar to the apparatus 180 shown in Figure 5 and includes the controlled current source 190 having the output 192, the controller 194 and the apparatus ground 196. The point 168 on the metallic pipe 160 of the pipeline 126 is coupled to the output 192 of the controlled current source 190 via a conduction path 302. The conduction path 302 is similar to the conduction path 182 shown in Figure 5 and the conduction path 252 shown in Figure 7. However, in this embodiment, the apparatus 300 further includes a resistive conduction path 320 to ground 322 which is coupled to the conduction path 302 at a node 324. A precision resistor 326 is coupled between the node 324 and the ground 322. In this embodiment, the node 324 is closer to the pipeline 126 than the controlled current source 190 and the resistive conduction path 320 is provided to shunt current into the node 324 away from the node 324 for current (or voltage) measurement purposes. Alternatively, a clamp-on type of current transformer may be used for current or voltage measurement purposes.

In the embodiment shown, current flowing out of the node 324 passes through the precision resistor 326 and develops a voltage across the precision resistor 326. This voltage is measured by a voltage sensor, which may be the measurement device described above at 198 to produce a 0-10 Volt measurement signal, for example, representing the voltage measured across the precision resistor 326. The measurement signal is for receipt by the controller 194 and may be communicated by wires 328 to the controller 194, for example. The controller 194 processes the measurement signal in a manner similar to that described in connection with the controller 194 in Figure 6 and produces a control signal for receipt by the controlled current source 190 to cause the controlled current source 190 to adjust the injection current \ n \ produced at the output 192 in the manner described above in connection with Figure 6. The control signal causes the controlled current source 190 to produce an injection current lj nj which functions to maintain the voltage across the precision resistor 326 in compliance with a criterion or at least one criterion, such as maintaining the voltage across the precision resistor 326 at or near zero. Due to the high conductivity and low impedance of the conduction paths 320 and 302, maintaining the voltage across the precision resistor 326 at or near zero generally indicates that the voltage at the node 324 is at or near zero, which in turn generally indicates that the voltage at the point 168 on the pipeline 126 is at or near zero. Accordingly, the peak of the induced emf that would normally have been measured at or near the point 168 is reduced or negated. The resistive conduction path 320 can take various different forms. For example, in some embodiments, the resistive conduction path 320 may be a metallic grounding rod. In other embodiments, the resistive conduction path 320 may be a coupon of the metallic pipe 160, which may facilitate the establishment of a threshold for the maximum allowable current that can flow through the resistive conduction path 320. For example, if the coupon has a current density higher than the threshold, corrosion of the pipeline is very likely to occur. In other embodiments, the resistive conduction path 320 may be a series capacitor, which may facilitate blocking any of the common mode current applied to the metallic pipe 160 by the ICCP system 280 that might flow from the metallic pipe 160 to the surrounding ground.

System

An apparatus described in any of the above embodiments can be used at respective points on the pipeline corresponding to a change in parallelism between the pipeline and a nearby power line. For example, referring back to Figure 1 , any of the embodiments described above can be used to inject an injection current into the pipeline 30 at any of points 74, 78, 82 and 86. The same type of embodiment need not be used at every point and different types of embodiments can be used at different points on the pipeline.

Thus, there is provided a system for reducing power-line induced voltages in a pipeline, the system comprising connecting an apparatus as described by any of the embodiments described above to respective ones of a plurality of nodes on respective conduction paths from respective points on the pipeline, the respective points on the pipeline being at or near points on the pipeline where respective changes in spacing between portions of the pipeline generally parallel to the power line occur. When two or more apparatuses are close to each other, such as less than 5 kilometers, for example, when one apparatus injects a current into the pipeline, it will affect the V po tentiai at the location of another remote apparatus. So this remote apparatus needs to adjust its current output accordingly.

To coordinate two or more apparatuses to adjust their output injection current to reduce the voltage profile on the pipeline, wireless signals, for example, can be transmitted among the apparatuses to facilitate coordinated current injection. The metallic pipe itself may alternatively act as a medium to transmit signals for coordination. Alternatively, two or more devices could adjust their output injection currents in steps and in sequence at different time intervals to achieve coordination and maintain coordination. For example, radio signals or signals communicated by the pipeline itself acting as a communication medium may be used to allow apparatuses of the type described to communicate with each other using known or new techniques to communicate changes in injection current supplied by each apparatus required to negate the voltage caused by induced emfs. Alternatively, two or more devices, for example, can adjust their injection currents in sequence, i.e. one at a time during pre-defined time intervals, so that each apparatus will tend to settle its output injection current at its own required value that causes a reduction in the voltage profile along the pipeline after a few trials and errors. The power line current does not normally vary sufficiently in one or two hours and the coordination of injection currents can be done in a few seconds, so setting the injection current outputted by each apparatus can occur, assuming the power line current remains constant.

While specific embodiments have been described and illustrated, such embodiments should be considered illustrative of the subject matter described herein and not as limiting the claims as construed in accordance with the relevant jurisprudence.