Report Of Seminar On Underground Cable Detection Technology 3n6c70

Underground Power Cable Detection and Inspection Technology Based on Magnetic Field Sensing at Ground Surface Level A SEMINAR REPORT Submitted by

ANAND K R in partial fulfillment for the award of the degree of Bachelor of Technology In ELECTRICAL AND ELECTRONICS ENGINEERING Of

MAHATMA GANDHI UNIVERSITY

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING KMEA COLLEGE OF ENGINEERING EDATHALA AUGUST 2016

CERTIFICATE This is to Certify that the seminar report entitled Underground Power Cable Detection and Inspection Technology Based on Magnetic Field Sensing at Ground Surface Level is a bonafide record of the work done by Mr./Ms. ANAND K R ,Roll No. 11 under our supervision, in partial fulfillment of the requirements for the award of Degree of Bachelor of Technology in Electrical and Electronics Engineering from Mahatma Gandhi University ,Kottayam for the year 2016- 2017. Designation, Dept of EEE Designation, Dept of EEE

Seminar Co-ordinator Seminar Guide Professor and Head Department of Electrical and Electronics Engineering

Date:……………….

ABSTRACT

In this paper, a novel technique based on magnetic field sensing is proposed for underground power cable detection and inspection. In this technique, the current sources of the underground power cables are reconstructed based on a set of measured magnetic field values at the ground surface level emanated by the electric currents carried by the underground power cables. The stochastic optimization technique developed with an artificial immune system algorithm is applied to realize the reconstruction. The principle of this method was proved and verified experimentally by our laboratory setup. Application of this method was demonstrated on the simulation models of 11- and 132-kV underground power cables. The reconstruction results of the electrical and spatial parameters of the cables match accurately with the actual source parameters of the cables in the models. This paper shows that the proposed method is able to remotely detect the horizontal locations and vertical depths of underground power cables with high accuracy at the ground surface level requiring no prior knowledge about the exact locations of the cables. Thus, it can be potentially used to develop a portable locator for providing a map of the underground electrical cables by simultaneous detection of multiple power lines. This method can also enable engineers to correctly inspect the operation states of the target cables during onsite maintenance.

This technique is applicable to various laying conditions and cable configurations (three core or single core) of the underground power cables. In addition, this is an entirely ive method and does not need any signal injection into the cables.

CONTENTS Chapter No: Page

ii Symbols

TITLE

L

List of Abbreviations List of iii List of Figures

iv List of Tables v 1 1

INTRODUCTION 1.1 1.2 1.3

2

2.1 2.2

Introduction Advantages of underground power cables Conventional methods of detection MAGNETO-RESISTIVE SENSORS

Basic principle 14 Construction 15

1 9 10 14

2.3

Applications 16 PROPOSED METHOD 17 Advanced Magnetic Sensing Using MR

3 3.1 Sensors 3.2 19 4 23 4.1 23 4.2 23

5 24

17 Algorithm ADVANTAGES Advantages

of

AND the

DISADVANTAGES proposed

systemm

Disadvantages

RESULT AND DISCUSSION 5.1 5.2

26 6 27

Result 25 Analysis SUMMARY

6.1

Conclusion

28 6.2

Future scope 29 BIBLIOGRAPHY APPENDIX-A

List of Abbreviations

AND

CONCLUSION

DC

- Direct Current

AC

- Alternating Current

EMF - Electro Motive Force MR - Magneto resistive I - Inverse Current Program MFE - Magnetic Field Evaluation SPO - Source Position Optimisation LSA - Least Square Optimization FEA - Finite Element Analysis

List of Symbols

Chapter 2 1 I – Current flowing through the MR sensor 2 M-Magnetisation Vector 3 M1-Magnetisation vector at point 1

Chapter 3 1 2 3 4 5

Po – Default Position Parameter Ip – Phase Current Bmea- Measured Value of Magnetic Feild Bcal – Calculated Value of Magnetic Field Ps – Randomly Generated Position Parameter

List Of Figures

FIG 1.3.2 -Process Of Conductive Injection FIG 1.3.3 -Process Of Inductive Injection FIG 1.3.4 - Process Of Detection By Magnetic Sensing FIG 2.1

-Magneto Resistive Effect

FIG 2.2

-Magneto Resistive Sensor

FIG 3.1

- MR Sensor Array Setup

FIG 3.2

-FLOW CHART

FIG 3.3.1 -3 PHASE 3 CORE POWER CABLE FIG 3.3.2 -SINGLE CORE POWER CABLE FIG 5.1 -AN EXPERIMENTAL SETUP OF THE PROPOSED TECHNIQUE FIG 5.2

-OUTPUT WAVEFORMS

FIG 6.1

- Prototype OF MR Module

T

CHAPTER 1 INTRODUCTION

Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution.

1.1 Introduction Electric Power needs to be carried over long distances from the point of generation to the point of consumption. This Transmission is done either through overhead lines or underground cables. Each of these two methods of transmission has its own advantages and disadvantages. conductor

Overhead Transmission lines are cheaper as the insulation cost is lesser and the material cost is lesser too. They also have better heat dissipation.

However, they have significant disadvantages. Overhead lines are vulnerable to lightning strikes which can cause interruption. Overhead lines use bare conductors and can cause damage if they break. They are considered to be unsightly as they mar the scenery of the landscape. The maintenance cost of overhead lines is more and the voltage drop in overhead lines is more. Electric power can also be transmitted by underground power cables instead of overhead power lines. Underground cables take up less right-of-way than overhead lines, have lower visibility, and are less affected by bad weather. However, costs of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. Underground lines are strictly limited by their thermal capacity, which permits less overload or re-rating than overhead lines. Long underground AC cables have significant capacitance, which may reduce their ability to provide useful power to loads beyond 50 mi (80 km). Long underground DC cables have no such issue and can run for thousands of miles.

1.2 Advantages Of Underground Power Cables



Less subject to damage from severe weather conditions (mainly lightning, wind and freezing)



Reduced range of electromagnetic fields (EMF) emission, into the surrounding area. However depending on the depth of the underground cable, greater emf may be experienced. The electric current in the cable conductor produces a magnetic field, but the closer grouping of underground power cables reduces the resultant external magnetic field and further magnetic shielding may be provided.



Underground cables need a narrower surrounding strip of about 1–10 meters to install (up to 30 m for 400 kV cables during construction), whereas an overhead line requires a surrounding strip of about 20–200 meters wide to be kept permanently clear for safety, maintenance and repair.



Underground cables pose no hazard to low flying aircraft or to wildlife.



Much less subject to conductor theft, illegal connections, sabotage, and damage from armed conflict.



Burying utility lines makes room for more large trees on sidewalks, which convey environmental benefits and increase property values

1.3 Conventional methods of power cable detection In metropolitan areas, most power cables are buried underground .Therefore, underground power cables must be detected before any excavation works to check if there are any buried power cables underground. When first introduced approximately 40 years ago, underground locators needed to do little more than find buried water, gas, or sewer lines. Today, locating has become more complex as telecommunications cables utility lines in the underground environment. Surprisingly, though, today`s underground cable locators rely on the same basic technology found in their early counterparts--injecting an electrical signal onto the cable being located.

1.3.1 The main detection methods used are listed below : a) Signal injection and detection i. ii.

Conductive injection Inductive injection

b) Magnetic sensing 1.3.2 Conductive injection

The conductive method employs the technique of transferring the transmitter signal to the power cable by direct . The transmitter is connected to the powercable at the nearest exposed site .

FIG 1.3.2 Process Of Conductive Injection

There are several possibilities for directly connecting the Transmitter to apply signal, including applying signal to the transformer, meter, and cable to be located. The one end of power cable is grounded so that the signal will return to the black terminal of the transmitter, hence completing the circuit. h

The receiver will then be used to detect these signals being transmitted through the cable and hence can trace the exact location of the cable through the ground.

1.3.3 Inductive Injection The inductive signal injection method is an advanced form of injection method which unlike the conductive injection method, it does not need a direct with the power cable inorder to inject the transmitter signal.The signal gets induced to the cable by electromagnetic induction.

a

Use the Inductive Clamp method to put tracing signal only on the neutral of primary energized cables and never on the primary cable itself. The neutral and its grounds form a circuit path for the signal to follow. When signal is applied with the Inductive Clamp to the neutral anywhere between grounds, signal will be on the section between the grounds.

The FIG 1.3.3 Process Of Inductive Injection receiver will then be used to detect these signals being transmitted through the cable h and hence can trace the exact location of the cable through the ground

1.3.4 Magnetic Sensing

g

Use a ive array of magnetic sensors together with advanced signal processing techniques to detect underground electricity cables. The location and depth of the subsurface pipe or cable is located by the angle of magnetic force concentrically generated by the metal pipe and the strength of the magnetic field.

The frame with its search coils are placed at a number of position above the search a area, and its position is recorded.The voltages induced in the coils are measured, and Fourier a analysis is used to extract the 50 Hz and harmonic signal components

FIG 1.3.4 Process Of Detection By Magnetic Sensing

FIG 1.3.4

Process Of Detection by magnetic sensing

1.4

Limitations of conventional methods

•

The signal injection method uses a transmitter and a receiver which make it more difficult to carry and it takes a lot of time to setup or initialize the process.

•

These devices only detect spatial parameters of the underground cables.

•

They cannot provide any electrical information in most cases.

•

In addition, it heavily relies on the expertise, experience, and judgment of the operator to properly locate the underground cables.

•

These tools are in principle just a magnetometer and they do not provide much analysis about the measured data.

•

These devices are very expensive

CHAPTER 2 MAGNETO-RESISTIVE SENSORS

2.1 Basic Principle The magnetoresistive sensors are based on the magnetoresistive effect. The magnetoresistive effect is the change of the resistivity of a current carrying ferromagnetic material due to a magnetic field. MR sensor can be called as magnetically controllable resistors. The below figure shows the Magnetoresistive effect.

FIG 2.1 Magneto Resistive Effect When the current is ed through the ferromagnetic material the internal magnetisation vector(M) of the ferromagnetic material is parallel to the current flow. When an external magnetic field is applied in applied opposite to the direction of the current flow as shown in the figure the internal magnetisation vector changes its position(M1) by an angle depending on the strength of the magnetic field. The resistance depends on the angle formed by the internal magnetisation vector(M) of the ferromagnetic material and the direction of the current(I) flow. Resistance is largest if the current flow and the internal magnetisation vector are parallel. The resistance in ferromagnetic material is smallest if the angle is 90° between the current flow and the internal magnetisation vector.

2.2 Construction

FIG 2.2 Magneto Resistive Sensor

Normally 4 sensors are connected in a Wheatstone bridge configuration to form a complete MR sensor with each resistor arranged to maximize sensitivity and minimize temperature influences. In the presence of a magnetic field, the values of the resistors change, causing a bridge imbalance and generating an output voltage proportional to the magnetic field strength. The Wheatstone bridge configuration provides reduction of temperature drift and doubles the signal output

2.3 Applications Of Magneto Resistive Sensors 

Wheel speed sensors



Angle measurement



Linear displacement measurement



Current measurement



Earth magnetic field detection for com and navigation applications



Metal detection



Magnetic field measurement

CHAPTER 3 PROPOSED METHOD To overcome the limitations of the conventional methods of detection, a novel technique based on magnetic field sensing is proposed for underground power cable detection and inspection.In this technique, the current sources of the underground power cables are reconstructed based on a set of measured magnetic field values at the ground surface level emanated by the electric currents carried by the underground power cables. The stochastic optimization technique developed with an artificial immune system algorithm is applied to realize the reconstruction.

3.1 Advanced Magnetic Sensing Using MR Sensors Nowadays, cable avoidance tools [7] are used to detect the underground power cables. This kind of device works in different modes. In ive mode (50/60 Hz), it provides the approximate horizontal location of the target cable. In active mode, it measures the depth of an underground cable with the aid of a signal generator that typically injects 33 kHz signal into the cable. However, these tools can only detect spatial parameters of the underground cables. They cannot provide any electrical information in most cases. In addition, it heavily relies on the expertise, experience, and judgment of the operator to properly locate the underground cables. These tools are in principle just a magnetometer and they do not provide much analysis about the measured data. A certified personnel is typically needed (it is required by law in many countries) to use this kind of tool to carry out underground cable detection.

FIG 3.1 MR Sensor Array Setup These cable avoidance tools are expensive particularly, the signal generators needed in active mode are costly. Therefore, it is of great application value to develop a novel detection and inspection technology for undergroundpower cables [8].According to Biot–Savart Law, a conductor carrying electric current generates magnetic field. The source current and the spatial location of the cable determine the distribution of the emanated magnetic field. Generally, a buried 11-kV 540 A underground power cable emanates magnetic field in the order of microTesla at the ground level. When the phase current varies, the ground-level magnetic field changes in magnitude and distribution correspondingly. Currently, commercially available magnetoresistive (MR) magnetic sensors can provide sensitivity down to around 10−9 T and spatial resolution of 0.9 mm [9]. Thus, the MR sensors installed on the ground level can accurately measure the emanated magnetic field distribution from the buried power cables. When a group of magnetic field values are measured, it is possible to reconstruct the spatial and electrical information of the underground power cables by solving inverse problem [10]. Previously, we developed a technique for monitoring operate state and identify energization status for underground power cables based on magnetic field sensing [11]. However, it has the limitation that the sensor array must be mounted around the cable surface which requires the cable to be dug out and exposed. To compensate for these limitations ,we developed a novel underground powercable detection and inspection technology based on magnetic field sensing at ground surface level without the need of excavating the cable. It operates in ive mode with no need for any signal injection and it can perform multicable detection. Using this technology, the horizontal locations and the vertical depths of the underground cables can both be remotely and accurately measured requiring no prior knowledge about the exact locations of the cables. In addition, it can inspect the operation states of underground power cables.

and provide more detailed information than the existing cable avoidance tools. Besides spatial parameters, it can provide detailed electrical parameters of the underground power lines, which are important for analyzing the power systems. For examples, when phase current imbalances are detected, the operator can diagnose the system operating in an unstable state. This technology can also provide the information of system frequency, which is the only parameter that can indicate the balance of the power system and reflect if supply–demand mismatch occurs.

3.2 Algorithm

FIG 3.2 FLOW CHART

Stochastic optimization technique is used to solve the inverse problem and reconstruct the horizontal locations, the vertical depths, and the electrical parameters of the target cable conductors from the magnetic field measured remotely at the ground surface level [10]. Two nested algorithms including least square approximation (LSA) and artificial immune system (AIS) are used in the optimization process [12], [13].

The whole process is described in the flowchart(Fig. 3.2). It starts with the default position parameters P0 of the underground cable conductors. Phase current Ip in each conductor is calculated by inverse current program (I) based on the LSA algorithm, with position parameters and measured magnetic field Bmea as variables by

Ip = (AT A)

−1

A

T

Bmea

- (1)

where A is the coefficient matrix which depends on the cable conductor positions. Then, the magnetic field Bcal is calculated using Ip and A in magnetic field evaluation (MFE) module based on finite element analysis (FEA) as [14], [15]

Bcal = AIp.

- (2)

There is a predetermined minimum threshold value of the Euclidean distance ||Bcal –Bmea|| as the end condition for terminating the optimization. If the end condition is not satisfied, the algorithm randomly generates a group of new position parameters Ps using AIS algorithm in source position optimization module. With the Bmea and the new Ps, the Ip is computed again in the I module. The new Ps and Ip are then used to simulate new Bcal in the MFE. When the Euclidean distance between the calculated Bcal and Bmea is smaller than the minimum threshold value, the optimization process is finished, and then the resulting Ps, and Ip are saved as the optimum current source parameters; otherwise, the iteration continues to loop. This optimization process is repeated multiple times (N) to obtain the final Ps which are the ensemble averages of these N optimum values. Accordingly, the final Ip is obtained from the final Ps and the measured magnetic field.

3.3 Applications

    

Can even be used to detect high voltage carrying cables up to 132 KV. It can be used to sketch the cable layout patterns in the region . It may be used to find faults in cables. May help excavation workers to avoid high power lines Can detect power cables that lie in any kind of layouts. FIG 3.3 & FIG 3.4

COMMON LAYOUT PATTERNS OF UNDERGROUND CABLES

FIG 3.3.1 3 PHASE 3 CORE POWER CABLE

FIG 3.3.2 SINGLE CORE POWER CABLE

CHAPTER 4 ADVANTAGES AND DISADVANTAGES

4.1 ADVANTAGES

•

High reliability due to its rugged construction.

•

Reasonable cost and small size.

•

Can detect not only the spatial parameters, but also the electrical parameters of the cable.

•

Placement of the magnetic sensor array is flexible.

•

Can detect multiple cables simultaneously.

•

can even be used to detect high voltage carrying cables up to 132 KV.

4.2

DISADVANTAGES

•

Sensitive to interfering magnetic fields. Very strong magnetic field can damage the sensor

•

Limited linear range

CHAPTER 5

RESULT AND DISCUSSION

5.1 Experimental setup

The figure shows the practical application of the detection technique using 3 phase power transmission through conductors A,B and C respectively.The array of magnetis sensors were placed above the conductors and magnetic fields were measured.

FIG 5.1 AN EXPERIMENTAL SETUP OF THE PROPOSED TECHNIQUE

5.2 Result •

The measured magnetic field values are very close to the values calculated analytically

•

Based on the measured magnetic field, the current source reconstruction was carried out to find out the spatial and electrical parameters of these three-phase power lines

•

The output waveforms are shown as in FIG 5.1

FIG 5.2 OUTPUT WAVEFORMS

5.3 Analysis

The sensor array consists of several MR three-axis sensors(Honeywell HMC2003) Aligned horizontally over the wires with ac voltages with frequency of 50 hz. It is worth noting that the placement of the magnetic sensor array is flexible and it does not need to be exactly above the cables to be detected as demonstrated by these two application examples. A horizontal offset of over a meter between the center of the sensor array and the cables can be tolerated, and accurate reconstructed results can still be obtained. It is highly advantageous to the practical application of this technique on site because in reality only rough locations of the power cables are provided by the underground cable route maps from the power companies.

CHAPTER 6 SUMMARY AND CONCLUSION 6.1 SUMMARY In this paper, we developed a novel underground power cable detection and inspection technology based on magnetic field sensing and current source reconstruction. When a group of magnetic field values are measured by a magnetic sensor array at ground surface level, current source reconstruction can be applied to solve the inverse problem and obtain the spatial and electrical parameters of the cables including horizontal location, vertical depth, and current information requiring no prior knowledge of the exact cable locations. Since the complete process is only based on the remote magnetic field sensing and current source reconstruction, it is a ive detection and inspection method with no need of any signal injection. In addition, it is able to detect multiple targets simultaneously. The principle of this technology was proved experimentally with our laboratory setup. We successfully applied and demonstrated it in the simulation models of 11-kV trefoil-formation and 132-kV flat-formation underground power cables. Thus, it is universally applicable for various laying conditions and configurations of underground power cables. This technology is feasible for detecting the positions and inspecting the operation states of underground power cables. It can help locating underground power cables before excavation works. It can be potentially used to develop a portable locator for providing a map of the underground electrical cables by simultaneous detection of multiple power lines. In addition, engineers can apply this technology to inspect the operation states of the underground power cables remotely without digging up the cables.

6.2 Future Scope

FIG 6.1 Prototype OF MR Module

This technology may be integrated with a fault detection system and also a movable setup is being developed to provide portable detection across wide range of area. Soon, this technology may be implemented on every construction work that involves trenching to check for under lying cables and hence avoiding it.

BIBLIOGRAPHY

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pp. 2608–2611, Oct. 2011. [11] X. Sun, G. Chan, C. Sum, W. Lee, L. Jiang, and P. Pong, “Operationstate monitoring and energization-status identification for underground power cables by magnetic field sensing,” IEEE Sensors J., vol. 13, no. 11, pp. 4527–4533, Nov. 2013. [12] F. Freschi and M. Repetto, “Comparison of artificial immune systems and genetic algorithms in electrical engineering optimization,” Int. J. Comput. Math. Electr. Electron. Eng., vol. 25, no. 4, pp. 792–811, 2006. [13] P. Neittaanmaki, M. Rudnicki, and A. Savini, Inverse Problems and Optimal Design in Electricity and Magnetism. New York, NY, USA: Oxford Univ. Press, 1996. [14] X. B. Xu and G. Liu, “A two-step numerical solution of magnetic field produced by ELF sources within a steel pipe—Abstract,” J. Electromagn. Waves Appl., vol. 14, no. 4, pp. 523–524, Jan. 2000. [15] X. B. Xu and G. H. Liu, “Formulation of a computational model for determining the magnetic field produced by an in-service underground pipe-type cable,” in Proc. IEEE SoutheastCon, Apr. 2002, pp. 99–103. [16] (2012, Oct. 18). EMFs info: Electric and Magnetic Fields [Online]. Available: http://www.emfs.info