Design and Experimental Study of Rail Degaussing System Based on

Permanent Magnet

Yongkang Li

and Yaowen Zhang

China Railway ERYUAN Engineering Group CO., LTD, C

heng

du, China

School of Physical Science and Technology, Southwest Jiaotong University, C

heng

du, China

Keywords: Rail Degaussing, Permanent Magnet, Electrified Railway, Abnormal Magnetic Signal.

Abstract: In order to eliminate the abnormal magnetic signal of electrified railway rail, a permanent magnet degaussing

array for rail was designed based on the mechanism of permanent magnet degaussing method. A permanent

magnet degaussing device suitable for rail was developed by degaussing array, and its function was verified.

The test results showed that the permanent magnet degaussing device can reduce the abnormal magnetic

signal of rail surface amplitude of 100Gs to less than 5Gs, which was lower than the automatic over-phase

induction threshold of locomotive 36Gs, indicating that the function of the degaussing device meet the

requirements.

1 INTRODUCTION

In the process of long-distance travelling, the

locomotive will pass through the power supply areas

of different traction substations, and there is an

automatic split-phase zone at the intersection of two

traction substations. In order to prevent phase-to-

phase short-circuiting, the automatic split-phase zone

is prohibited from energizing, and the locomotive

needs to independently complete the disconnecting

and closing action of the main circuit breaker in this

zone. In the automatic over-phase area of the entrance

and exit are set up in the buried magnet, locomotive

head is equipped with a sensor, when the locomotive

passes through the magnet, the inductor will receive

the magnetic signal and send out a pulse signal,

transmitted to the microcomputer system to control

the main circuit breaker opening and closing. In the

process of locomotive travelling, if the abnormal

magnetic signal from the rail surface is larger than the

sensing threshold of the car inductor 36Gs (Li Teng,

2022; Li Lifeng, 2022; Ma Chunlian, 2022), the car

inductor can also sense the signal, which leads to an

abnormal tripping of the main circuit breaker of the

locomotive, and has an impact on the normal

operation of the locomotive. The maximum remanent

magnetism of the rail has reached 100Gs by the

railway field measurement, therefore, eliminating the

abnormal magnetic signal is of great significance for

the normal operation of the locomotive.

The traditional demagnetization methods for

magnetic pipes in industry are DC demagnetization

method, AC demagnetization method and DC-AC

composite method (Tan Xiao, 2020; Liu Shaozhu,

2020; Xu Congcong, 2020), but these methods are not

applicable to the demagnetization of rails. Because

the rails are fixed on the railway, it is not possible to

wrap the cable around them, and the high-voltage

power supply required for degaussing by DC and AC

degaussing method is not suitable for field operation.

Permanent magnet demagnetization method is used to

demagnetize workpieces by arranging the magnets

without the need for power supply and winding

cables, which overcomes the drawbacks of the

traditional demagnetization methods and is suitable

for demagnetization of steel rails. A permanent

magnet demagnetization device has been developed

for oil and gas pipelines by the team of Shelikhov G

S, which consists of two to three rings of magnets,

with the polarities of the neighbouring rings arranged

in opposite directions. magnetic field with reduced

amplitude and direction change, so as to achieve the

purpose of demagnetization. In order to eliminate the

residual magnetism of oil and gas pipelines after

leakage detection, Yang Xiaoli designed a

demagnetizing device that can walk inside oil and gas

pipelines, which is installed with two magnet rings

with opposite poles and different mounting heights,

Li, Y. and Zhang, Y.

Design and Experimental Study of Rail Degaussing System Based on Permanent Magnet.

DOI: 10.5220/0012875900004536

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Data Mining, E-Learning, and Information Systems (DMEIS 2024), pages 17-21

ISBN: 978-989-758-715-3

and generates a decreasing commutative magnetic

field in the process of walking to demagnetize the

pipelines. The robot designed by Zhang Jiawei can

adapt to the variable diameter pipe and detect

efficiently, according to the magnetization simulation

of typical deformation types and deformation of

different lengths and widths, the basic law of

magnetic field intensity change is obtained: the types

and characteristics of deformation in pipelines can be

predicted according to the simulation parameters,

which is of significance for the development of

deformation detection technology in oil and gas

pipelines. The rotating permanent magnet

demagnetization machine designed by Li Xibi uses

rare earth permanent magnet material NdPeB as a

magnetic source to make a magnetic roll or abstract

disk, and uses a small power motor to drive it to turn,

and generates an alternating magnetic field in space

to demagnetize the workpiece. The demagnetization

field has adjustable frequency and magnetic field

gradient, high work efficiency and long service life.

At present, the permanent magnet degaussing method

has limited application scenarios, and has not been

studied in depth in the railway field, and the magnetic

field amplitude that can be eliminated by the existing

permanent magnet degaussing device for oil and gas

pipelines is relatively small, and the research on the

degaussing mechanism of permanent magnet is not

in-depth and detailed enough, and the relevant

degaussing method has not formed a system.

Therefore, the development of permanent magnet

degaussing device for rails is necessary.

Based on the principle of permanent magnet

degaussing, a permanent magnet degaussing array is

designed in the paper. According to the degaussing

array, rail structure and railway environment, the

permanent magnet degaussing device is developed,

and the degaussing effect of the permanent magnet

degaussing device is examined through the function

verification test.

2 PRINCIPLE OF PERMANENT

MAGNET DEMAGNETISATION

The demagnetization of magnetic materials generally

takes advantage of their hysteresis properties. For

workpieces with a certain amount of remanent

magnetization, the core of the demagnetization

method is to apply a decreasing and alternating

magnetic field to the remanent magnetized parts. The

traditional method of demagnetization in industry is

to wind a cable around the workpiece, energize the

cable, and change the size and direction of the current

to produce a variable magnetic field on the surface of

the workpiece, as shown in Fig. 1 for the magnetic

field amplitude curve of the AC demagnetization

method. Permanent magnet demagnetization is

achieved by increasing the distance between the

magnet and the surface of the workpiece and

changing the N and S poles to achieve changes in the

magnetic field.

Figure 1: Magnetic field amplitude curve of AC degaussing

method.

3 DESIGN OF DEGAUSSING

ARRAYS

3.1 Arrangement of Degaussing Units

From the principle of demagnetization, it can be seen

that the magnet array needs to generate a

commutative magnetic field with decreasing

amplitude during the movement, so the magnet units

are arranged in a stepped row, and the magnetic poles

of two adjacent magnet units facing the surface of the

rail are opposite. As shown in Fig. 2, the black unit is

the permanent magnet, and the rail is below. The

degaussing array generates an AC-like magnetic field

on the rail surface.

Figure 2: Arrangement of degaussing units.

3.2 Parametric Design of Degaussing

Arrays

As shown in Fig. 3 for the relevant parameters of the

rail degaussing array, the number of degaussing units

is set to three in order to make the degaussing array

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not to affect the unmagnetized area and not to cause

waste. When the magnetic field of the rail surface for

the N pole, it is composed of three magnets array N-

S-N to eliminate it; when the magnetic field of the rail

surface for the S pole, it is composed of the last two

magnets S-N to eliminate it; when the surface of the

rail is not magnetized, the first magnet magnetized

rail, the last two magnets composed of an array S-N

can eliminate the effect. The parameters to be

determined for the demagnetizing array are the

horizontal spacing between the magnet units as d and

the vertical distance between the lower surface of the

magnet units and the rail surface l

Figure 3: Arrangement of degaussing units.

In order to make the magnet units unaffected by

each other, it is necessary to determine the maximum

range of action of the magnet's magnetic field. The

three sizes of rectangular NdFeB magnets used in the

degaussing array have a maximum field range of 90

mm, so the horizontal spacing d of the magnet units

in the design of the magnet array should be greater

than 90 mm, and the horizontal spacing d is taken to

be 100 mm.

From the principle of permanent magnet

demagnetization, it can be seen that the

demagnetization process of the permanent magnet on

the rail is the process of using the attenuating

magnetic field to make the hysteresis line constantly

converge to the origin of the coordinates. Therefore,

before designing the demagnetizing height of the

demagnetizing array, it is necessary to obtain the

hysteresis lines corresponding to different remanent

magnetism of the rails. The rail is made into a circular

sample as shown in Fig. 4, Fig. 5 is the experimental

schematic diagram, the hysteresis line of the sample

is measured by the oscilloscope method, the test loop

is divided into the excitation loop and the induction

loop, the excitation loop is energized with an AC

power at an industrial frequency, and then the voltage

at the ends of the sampling resistor and the

capacitance at the ends of the RC integrator are

measured, and the voltage data are then calculated to

obtain the hysteresis line of the rail, and the hysteresis

line of the rail can be obtained by changing the

amplitude of the excitation voltage. By changing the

amplitude of the excitation voltage, different

hysteresis loops can be obtained. The three hysteresis

lines corresponding to the rails with remanent

magnetism of 125Gs, 62Gs and 32Gs are obtained

through experiments, and the perpendicular distances

, l

and l

from the magnet unit to the plane of the

rails are determined to be 6mm, 12mm and 18mm,

respectively.

Figure 4: Samples of rail rings with coils wrapped around

them.

Figure 5: Hysteresis loop test schematic.

The equivalent magnetic circuit equation of the

excitation circuit can be expressed as:

NI Hl=

(1)

(2)

(3)

Where H is the intensity of the excitation magnetic

field, I is the current of the excitation loop, U

is the

voltage of the excitation loop, R

is the resistance of

the excitation loop, N

is the number of turns of the

excitation coil, and l is the average length of the

measured magnetic circuit. A channel of the

oscilloscope is connected to both ends of the

sampling resistor R1 to measure its voltage, and then

the measured voltage data can be converted into

magnetic field strength data.

The equivalent magnetic loop equation of the

detection loop can be expressed as:

RC U N S

dt dt

(4)

=−

(5)

Design and Experimental Study of Rail Degaussing System Based on Permanent Magnet

Where B is the magnetic induction intensity of the

rail sample after magnetization, resistance R

and

capacitor C constitute an integral circuit, and the

value should meet , U

is the voltage at both ends of

the capacitor, N

is the number of turns of the

detection coil, and S is the sample cross-section area.

The other channel of the oscilloscope is connected to

both ends of the capacitor C to measure its voltage,

and then the measured voltage data can be converted

into magnetic induction intensity data. Alternating

current changes one cycle, the oscilloscope can

display a complete hysteresis loop of the magnetic

material sample, if you want to measure the hysteresis

loop corresponding to different coercivity and

remanence, just change the voltage amplitude of the

AC power supply.

The final design of the permanent magnet

degaussing array is shown in Fig. 6. Five groups of

degaussing arrays are set up for the whole rail, one

group of degaussing arrays is set up on the top

surface, and two groups of degaussing arrays are set

up on the left and right sides of the top side and the

middle surface, and they are symmetrically

distributed. The parameters of each array are

consistent except for the size of the magnet unit.

Figure 6: Permanent magnet degaussing array.

4 DEVELOPMENT OF

PERMANENT MAGNET

DEGAUSSING DEVICE

4.1 Model of Permanent Magnet

Degaussing Device

Based on the permanent magnet degaussing array, rail

structure and railway environment, a model of the

permanent magnet degaussing device was designed

and a sample of the permanent magnet degaussing

device was developed, and the model and sample of

the permanent magnet degaussing device are shown

in Fig. 7.

1-Hand screwed bolt 2- Top magnet fixing platform

3- Both sides magnet fixing platform 4- Roller

5- Anti-vibration slot 6- Fixing bolt 7- Pressure plate

8- Handle

Figure 7: Model of permanent magnet degaussing device.

4.2 Model of Permanent Magnet

Degaussing Device

After magnetizing the rail surface, the permanent

magnet demagnetization device is used to

demagnetize the rail, and the demagnetization process

is shown in Fig. 8. From the demagnetization results

in Fig. 9, it can be seen that the magnetic field on the

rail surface can be demagnetized to within 5Gs, which

is lower than the induction threshold of 36Gs for the

locomotive inductor, indicating that the

demagnetization effect meets the requirements. After

the demagnetizing device passes through the

unmagnetized area of the rail, the magnetic field on

the rail surface does not change by more than 5Gs, so

the influence of the demagnetizing device on the

unmagnetized area can be ignored when walking on

the rail surface.

Figure 8: Degaussing experiment diagram.

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Figure 9: Degaussing experiment diagram.

5 CONCLUSIONS

Based on the degaussing mechanism of permanent

magnets, a linear stepped degaussing array was

constructed in the paper, and the parameter design of

the degaussing array was completed according to the

principle of degaussing of permanent magnets and

magnetic characteristics of rails, forming a permanent

magnet degaussing system for rails. Based on the

degaussing array, rail structure and railway

environment, a permanent magnet degaussing device

for rails was developed in the paper, which

overcomes the shortcomings of the traditional

degaussing device that requires power supply and

winding cables, and was more portable and safe. The

permanent magnet degaussing device was tested for

functional verification, and the test results showed

that the degaussing effect of the device on rails meets

the requirements, and it had strong applicability for

degaussing of rails in electrified railways. The

degaussing device has a strong inspiration for the

development of rail mature degaussing equipment in

the future.

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Magnetic field size/Gs

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Design and Experimental Study of Rail Degaussing System Based on Permanent Magnet