A Study on the Electromagnetic Environment and Experimental Simulation of Electrified Railroad Mobile Catenary

Abstract

The mobile catenary is installed in the railway loading and unloading line, which could significantly increase the railway freight volume, provide a practical and efficient alternative to the traditional mobile catenary, and greatly improve the sustainability of electrified railroad freight transport. The increase in freight volume also leads to greater traction load and a more complex electromagnetic environment. To study whether the electromagnetic environment when the mobile catenary works meets the power frequency electromagnetic field exposure limit stipulated by the International Commission on Non-Ionizing Radiation Protection, this paper performed an experiment on the sunken mobile catenary. The results showed that the maximum magnetic induction intensity near the ground is 0.03 mT, and the peak electric field intensity on the ground is 1.1 KV/m. The finite element software is adopted to establish the pantograph–catenary model and mobile catenary model according to Principles of Electric Field Calculation and Finite Element Theory, and the space electric field is numerically simulated to study the changes in electric field intensity and distribution of electric field in catenary when the catenary arc occurs. The simulated results are basically consistent with the experimental results, to verify the reliability of the simulation model, which could effectively solve the difficulty and high cost of the experiment. The conclusion proves that the equipment meets the regulations and it highlights the potential, which provides a cost-effective and scalable solution for the electromagnetic environment when the mobile catenary works.

1. Introduction

In the context of global carbon neutrality, the electrified railroad, as a sustainable mode of transportation, has been favored by countries around the world due to high economic performance, low pollution level, and fast operating speed, and it plays an important position in the comprehensive transportation system [1,2]. Electric traction has become the mainstream development trend of the railway power [3]. With the rapid development of the electrified railroad transportation technology, the freight transport tasks by rail are increasing, and the application scenarios of mobile catenary have been more and more extensive [4]. When the freight train arrives or departs from the station, the electric locomotive is powered by the mobile catenary. When the freight train enters the station for loading and unloading operations, the catenary is removed to facilitate loading and unloading. At present, there are rigid and flexible catenary systems [5,6,7,8,9]. The rigid mobile catenary is prone to the impact of weather, temperature difference, and other factors, and it has features such as high costs, large maintenance, and long conversion time of operating status. The arch transition of the flexibility mobile catenary pantograph is smooth, the cost and the failure rate are low, and the transition time of operating status is short [10]. When the mobile catenary is installed in the railway loading and unloading line, this could solve the low efficiency under the traditional fixed catenary mode, significantly increase the traffic volume, and improve the sustainability of electrified railroad freight.

With the continuous construction of electrified railways and the rapid development of high-speed trains, there is more and more electrical equipment for power supply and consumption on high-speed trains, which makes the analysis of electromagnetic distribution of high-speed train power supply systems more complicated. Meanwhile, the promotion of the mobile catenary will increase the traction load and make the electromagnetic environment more complex. The increase in traction power leads to an increase of the traction current through the mobile catenary and enhances the coupling effect on the surrounding metal conductors. Wherein, the higher harmonic current will have a more significant impact on the surrounding electromagnetic environment [11]. As a special form of asymmetric high-voltage transmission line, the traction power supply system for electrified freight railway generates induced voltage or induced current to nearby loading and unloading lines under electromagnetic radiation. Electrical sparks may occur in contact and friction between equipment during loading and unloading operations, which may cause hazardous accidents and interrupt the system construction and development [12,13]. The researchers have made much research progress on EMDs (Electromagnetic Disturbances) and EMC (Electromagnetic Compatibility), and prove that electromagnetic interference is indeed an important factor that affects the normal operation of equipment and the physiological state of organisms. It is necessary to conduct in-depth research on the electromagnetic disturbance of the railway system and improve the electromagnetic compatibility. When the high-speed train is powered through the mobile catenary, the primary interference to the electromagnetic environment originates from the interaction between the pantograph and the catenary. As the voltage and current fluctuations caused by the pantograph–catenary arcing intensify, their impact on the electromagnetic environment becomes more significant. Additionally, factors such as the material composition of the catenary, structural parameters, and operational speed can influence the distribution of electromagnetic fields. The electromagnetic radiation generated by the pantograph–catenary off-line arc is the most important electromagnetic factor of the high-speed railway system. At present, relevant scholars have conducted much research on the sensitivity analysis and optimization on the key parameters of rigid catenary and the pantograph [14]: A Study on Mechanism and Characteristics of Off-line Discharge disturbance of pantograph [15]; Impact and Interference of Electromagnetic Field on Electronic Products [16]; Impact of Electromagnetic Environment on Human Body under the Electrified Railroad High-voltage Line [17,18]; Electromagnetic Interference Effect and Electromagnetic Compatibility of Pantograph Offline Catenary Arc [19,20,21]; as well as arc model [22]. However, there are few studies on the electromagnetic problems of electrified railroad mobile catenary, and the railway freight loading and unloading lines have more complex environments. Therefore, the increase in traction power and traction current also causes more severe electromagnetic interference to the surrounding loading and unloading equipment and goods transport, which is a potential threat to staff. To ensure the safety of the loading and unloading lines and improve the sustainability of the electrified railroad freight transport, it is necessary to study the electromagnetic environment of the mobile catenary.

To study whether the electromagnetic environment meets the exposure limit of power frequency electromagnetic field stipulated by ICNIRP (International Commission on Non-Ionizing Radiation Protection) Guidelines for Limiting Exposure to Time Varying Electric, Magnetic and Electromagnetic Fields (Below 300 GHz) when the mobile catenary is running [23], and cope with the electromagnetic security challenges for the future development of rail freight, this paper conducts an experiment on the sunken flexibility mobile catenary, measures the potential of the contact line and the magnetic induction intensity near the ground at its working position, and carries out the analysis and calculation of the electric field intensity, which provides important data support for the simulation study. Although the measurement method by experiment is intuitive and reliable, the measurement of the electromagnetic environment is prone to the impact of testing instruments, extreme environments, and measurement methods, resulting in a blind spot or blind area in the measuring process. Hence, there is a certain deviation for measuring results, and the experimental operation is difficult and costly. To solve this problem, this paper chooses the finite element software COMSOL Multiphysics 6.1 to construct the pantograph–catenary model and catenary model and numerical simulation of spatial electromagnetic fields. The model parameters are modified and adjusted to verify the reliability of the simulation model calculation.

2. Experiment

The high-speed freight railway power supply system generally adopts a 27.5 KV power frequency high-voltage AC line, and the minimum height is less than 5 m between the contact line and loading and un-loading platform. The implementation of fixed catenary in freight yards will encroach upon the overhead loading space, thereby limiting the operational efficiency and deployment of large-scale loading equipment. In recent years, railway loading lines have relied exclusively on diesel locomotives for loading operations. While this approach ensures unobstructed overhead space above trains, it introduces significant challenges, including reduced transportation efficiency, substantial environmental pollution, and the need for frequent shunting operations. These issues pose considerable obstacles to the sustainable development of electrified railways. The train could enter and exit the loading and unloading platform after the mobile catenary is installed compared to the previous freight railway. To enhance the efficiency of railway freight loading and unloading operations, improve the sustainability of electrified railways, and minimize the waste of time, machine power, and manpower caused by fixed catenary, railway trunk transportation increasingly favors electric locomotives over diesel locomotives for electrification on cargo loading and unloading lines. Consequently, it is necessary to install mobile catenary at freight stations and adopt an electric power connection design for loading and unloading lines to facilitate the direct entry and exit of freight trains. However, the mobile catenary has a shorter interval distance and higher suspension elasticity than the ordinary catenary pillars. Additionally, the frequent lifting and lowering of the pantograph is required, which may lead to more frequent catenary arc. This paper takes the sunken mobile catenary as an example for experimental research.

2.1. Two States of Sunken Mobile Catenary

There are working and non-working static states of the sunken mobile catenary. It takes 150 s to convert from the working position to the non-working position on average, and the average time of reserve operation is 240 s, as shown in a and b of Figure 1.

In the electrified section, most loading and unloading lines that accommodate whole-train entry and exit conditions are designed for open-top boxcars. When front-end lifting is employed for loading and unloading operations, these cannot be performed under fixed catenary systems. Consequently, the entire train must first be connected to a departure line and then transferred to the loading and unloading line via an internal combustion shunting locomotive. This shunting method fails to achieve direct entry and exit, leading to significant inefficiencies and manpower waste. Specifically, each station requires at least six shunting personnel, further exacerbating operational inefficiency. The implementation of a mobile catenary system can effectively address these issues by reducing time consumption, enhancing transportation efficiency, eliminating carbon emissions from diesel locomotives, and promoting the sustainability of electrified railways. The mobile catenary lies in the working position when the electric locomotive is powered on, and it moves to the non-working position when the goods are loaded or unloaded. The plugging parts of the mobile catenary are OFF and the catenary is not live when it moves from the working position to the non-working position. After the mobile catenary moves to the non-working state, multiple-wire induced fluids are connected to the grounding device at the non-working position through plug-in connection, to ensure that there is no electric charge on the catenary, so only the state of the working position is considered when the electromagnetic environment is analyzed.

2.2. Experimental Overview

To analyze and calculate the electromagnetic environment of the sunken mobile catenary at the working position, the experiment research was carried out in the sunken mobile catenary base established in 2023. The experiment site is shown in Figure 2.

Figure 3 shows the sunken mobile catenary system model.

• Height of contact wire suspension point: 6.3 m;
• The contact wire type is CTHA85, and the radius: r = 5.25 mm;
• Catenary potential: Φ = 27.5 KV.

2.3. Experiment Results

When the mobile catenary is in the working position, the potential is measured at the checkpoint on the contact line boundary using the high-voltage measuring instrument (Zhuochuan Tech, Dalian, China), and the check potential is shown in

Table 1. Electric potential.

	X/m	Y/m	Check Potential/V	Catenary Potential/V	Error
1	0	6.46050	27,049	27,500	0.01640
2	−0.00371	6.45896	27,050	27,500	0.01636
3	0.00371	6.45896	27,049	27,500	0.01600
4	−0.00469	6.39042	27,132	27,500	0.01338
5	0.00469	6.39042	27,133	27,500	0.01334
6	−0.00493	6.18746	27,226	27,500	0.00996
7	0.00493	6.18746	27,220	27,500	0.01018
8	−0.00525	6.00501	27,276	27,500	0.00814
9	0.00525	6.00501	27,276	27,500	0.00814

.

It could be found from Table 1 that the relative error is less than 0.05, meeting the requirements of engineering accuracy. The potential of the contact line is shown in Figure 4. It is used to simulate the electric charge into Formulas (1)–(3) and calculate the electric field intensity and composite field strength in different directions at a height of 1.5 m, i.e., P (X₀, 1.5). The calculation results are shown in Figure 5.

• Horizontal direction:

$$E_x=3522.4\left({\displaystyle \frac{x_0}{x_0^2+{4.95}^2}}-{\displaystyle \frac{x_0}{x_0^2+{7.95}^2}}\right)$$

(1)

2.

Vertical direction:

$$E_y=3522.4\left({\displaystyle \frac{-4.75}{x_0^2+{4.95}^2}}-{\displaystyle \frac{7.95}{x_0^2+{7.95}^2}}\right)$$

(2)

3.

Composite field strength:

$$\overrightarrow{E}=3522.4\left({\displaystyle \frac{x_0}{x_0^2+{4.95}^2}}-{\displaystyle \frac{x_0}{x_0^2+{7.95}^2}}\right)\overrightarrow{e_x}+3522.4\left({\displaystyle \frac{-4.75}{x_0^2+{4.95}^2}}-{\displaystyle \frac{7.95}{x_0^2+{7.95}^2}}\right)\overrightarrow{e_y}$$

(3)

y1, y2, and y3 in Figure 5 represent the horizontal, vertical, and composite field strength at a height of 1.5 m. It could be found from the table that the horizontal and vertical components of the electric field intensity at a height of 1.5 m are symmetrically distributed. There is an obvious downward trend from the left and right sides to the external electric field, and the electric field intensity near the ground is mainly determined by the vertical component. The maximum value of the synthesized field strength appears directly below the catenary, and the peak of the electric field intensity is about 1.1 KV/m, which does not exceed the control limit of the power frequency electric field intensity (4 KV/m). The safety coefficient is greater than 50 V, with sufficient safety.

2.3.1. Electric Field Intensity at Different Heights

The electric field intensity at different heights is measured for the working position of the sunken mobile catenary. The results are shown in Figure 6.

y1, y2, y3, and y4 in Figure 6 refer to the electric field intensity at the height of 1.5, 3.0, 4.5, and 6.0 m above the ground. It could be found that there is little difference in the electric field intensity curve at a horizontal distance over 5 m from the mobile catenary, there is large difference within 5 m and the maximum value is 8100 V/m at the height of 6.0 m above the ground. The closer the same location is to the contact line, the greater the electric field intensity.

2.3.2. Magnetic Induction Intensity near the Ground

Due to the 27.5 KV power frequency AC high-voltage circuit of electrified railways, a 50 Hz electromagnetic field is generated around the overhead catenary system. This field is pervasive throughout various aspects of railway operations and poses potential occupational hazards to workers in the electrified railway sector. The impact of power frequency electromagnetic fields (EMFs) on human health has garnered significant attention from scholars both domestically and internationally, with its potential hazards becoming a prominent research focus in bioelectromagnetics. The World Health Organization (WHO) and the International Agency for Research on Cancer (IARC) have integrated extensive epidemiological and laboratory research data, classifying power frequency EMFs as possible carcinogens. ICNIRP changed the reference level for public exposure of power frequency magnetic induction intensity to 0.2 mT (0.1 mT in the original guidance) in Guidelines for Limiting Exposure to Time-varying Electric and Magnetic Fields (1 Hz–100 KHz) published in 2010.

The maximum magnetic induction intensity measured near the catenary (6 m above the ground) is 0.35 mT using the experimental digital Gaussian meter magnetic induction measuring instrument (Dexinmag, Xiamen, China). The magnetic induction intensity at a distance of 1.5 m near the ground is on the order of 10⁻² mT, and the maximum value is 0.03 mT, which does not exceed the exposure reference limit stipulated in ICNIRP.

2.3.3. Influence of Different Conditions

The influence of different conditions on the electric field intensity at 1.5 m from the ground is tested.

• The electric field distribution with its own weight load of ${\mathrm{g}}_{\mathrm{j}}=7.54\times {10}^{-3} \mathrm{K}\mathrm{N}/\mathrm{m};$
• The electric field distribution under the influence of conductor icing 2.5 mm and wind speed 25 m/s.

As shown in Figure 7, the curve y1 considers the dead weight load of the conductor, and the curve y2 takes the impact of ice and wind into account. There is little difference for the electric field intensity under two circumstances; the curves basically coincide and there is only little difference in field strength directly below the contact line. The electric field intensity measured by the experiment increases by 110 V/m under two circumstances and the magnetic induction intensity increases by 0.004 mT. It proves that there is certain normal operating capacity for the sunken mobile catenary under the complex environment.

3. Simulation

The real data of the mobile catenary electromagnetic environment could be obtained through an experiment in actual circumstances, and it is of great significance to understand the working situations. However, there are numerous variables and sources of interference in the field environment, which may lower the repeatability of the experiment results [24]. Hence, relevant researchers have adopted simulation methods for studies, and the finite element method has become the most widely used method in modeling [25,26]. The finite element method discretizes the originally continuous structure and establishes the differential equation for each unit, and forms the overall system of linear equation after linearization [26,27].

During the running process of the mobile catenary, it is difficult to adjust the traction current and other parameters on time based on the demands. To solve the test measuring difficulties and high expenses, this paper chooses the finite element software COMSOL to conduct the simulation analysis of electric field distribution of the sunken mobile catenary.

3.1. Calculation Theory and Boundary Conditions

The electromagnetic field is calculated based on Maxwell’s equations, and its modern general form mainly consists of four equations, including curl and divergence of electric field and magnetic field, which indicates the relationship of electric field and magnetic field: a changing electric field could produce a magnetic field and the changing magnetic field could produce an electric field [28]. Differential mathematical expression of Maxwell’s equations:

$$\nabla \times H=J+{\displaystyle \frac{\partial D}{\partial t}}$$

(4)

$$\nabla \times E=-{\displaystyle \frac{\partial B}{\partial t}}$$

(5)

$$\nabla \times B=0$$

(6)

$$\nabla \times D=\rho$$

(7)

In the formula, B denotes the magnetic induction intensity (T); D represents the electric displacement vector (C/m²); H represents the magnetic field strength (A/m); and J represents the current density (A/m²).

Using the Gauss theorem and Stokes theorem, the corresponding integral mathematical expression is derived as follows:

$$\left\{\begin{array}{c}{\oint }_{S}DdS=q\\ {\oint }_{\tau }Edl=-{\oint }_S{\displaystyle \frac{\partial B}{\partial t}}dS\\ {\oint }_{S}BdS=0\\ {\oint }_{\tau }Hdl=I+{\oint }_S{\displaystyle \frac{\partial D}{\partial t}}dS\end{array}\right.$$

(8)

In the actual electromagnetic field, the boundary problem of the conductor will be encountered. The boundary conditions of an ideal conductor can be expressed as:

$$\left\{\begin{array}{c}n\times E=0\\ n·D={\rho }_S\\ n\times H=J_S\\ n·B=0\end{array}\right.$$

(9)

In the formula, $n$ denotes the normal unit vector from region 1 to region 2 on the interface.

Maxwell’s equations and boundary conditions form the foundation in evaluation of the electric field problems, and a practical electric field problem refers to the evaluation of Maxwell’s equations under certain boundary conditions.

3.2. Characteristics

Sunken mobile catenary equipment runs in complex operating environments. To facilitate the modeling analysis and numerical calculation, certain approximations are taken for some conditions.

• The power frequency alternating electric field is taken as a quasi-static field.

Under the quasi-static electric field conditions, the delay effect in wave propagation is negligible. When the source and the field are the functions of time and space, it indicates that the values at a certain time source have been given and the field at the same time is also determined, which is irrelevant from the state of early instant sources to simplify calculation. The electric field arising from the mobile catenary studied in this paper meets the quasi-static field conditions, so the power frequency alternating electric field is taken as the quasi-static field.

2.

We take the three-dimensional electric field as a two-dimensional field.

We omit the accidental factors such as extreme weather and other nearby objects, omit the end effect and sag phenomenon, regard the contact line as an infinite long, straight, and parallel line to calculate the plane perpendicular to the cross-section of the lowest point of the conductor sag or the symmetrical plane of the contact line direction.

3.

We consider the ground as the infinite conductor surface and the potential as zero, take the freight platform, gantry cranes, other freight equipment, transported goods, vehicle bodies, and steel rails as conductors with good grounding.

3.3. Modeling

When the mathematical model of catenary arc is evaluated, the boundary conditions and initial conditions of the arc simulation model shall be firstly set. The contact line and the pantograph carbon sliding plate are set as the anode and cathode of the catenary arc, respectively, which serve as the emitter to emit electrons and the receiver to receive electrons. The pantograph–catenary model is established as shown in Figure 8, and the mesh division is shown in Figure 9, where there is no arc. The initial ambient temperature is 300 K, the system pressure is 1 atm, the current of the pantograph system is 100 A, and the pantograph gap is 4 mm. In the arc simulation system, the thickness of the air solution domain is set to 450 mm, and the pressure of the system fluid is set to 1.2 atm. The boundary conditions for the wall surface and air convective heat transfer of the pantograph–catenary system are set as the forced convection mode, so the convective heat transfer coefficient of the pantograph–catenary arc system is set as 110 W/(m²·K). The pantograph–catenary arc heat flux density is set as 9.6¹⁰ W/m². The off-line air gap of the pantograph–catenary is set to 2 mm. The electrical conductivities of pure copper contact wire and copper-impregnated carbon slide are 4.167 × 10⁷ and 2.857 × 10⁶ S/m, respectively.

The diameter of the contact wire in Figure 8 is 10.50 mm. In order to simplify the calculation, the pantograph slide is regarded as a rectangle with a thickness of 20 mm.

The material of the contact wire is pure copper, and the material of the pantograph slide plate is copper-impregnated carbon. The physical parameters are shown in

Table 2. Physical parameters of contact wire and pantograph slide.

	Density/kg·m−3	Heat/J·(kg·K−1)	Heat Conduction/W·(m·K−1)
Pure copper contact wire	8950	385	400
Copper-impregnated carbon slide	2400	480	160

:

The contact line and the rail subgrade are set as per the size of the sunken mobile catenary system. The three-dimensional spatial and geometry model is established with a contact line distance of 6.0 m from the track, a length of 10 m for both the contact line and the track, a height of 0.3 m from the ground for the steel rail, and a contact line potential of 27.5 KV, as shown in Figure 10.

When the electric field under the transmission line of the mobile catenary is calculated, the potential of the rail and infinity is set to zero. According to the literature [29], this model is simple, but it could ensure the accuracy of simulating the distribution of electric fields in actual situations.

3.4. Simulation Results

This paper chooses the finite element software COMSOL to conduct the simulation studies on the occurrence of catenary arc and the electric field environment of the catenary, and calculate the discharge current density of the catenary arc. The calculation results are taken as the excitation sources of the simulation model of the mobile catenary electric field to obtain the spatial distribution and attenuation characteristics of the electric field when the catenary arc occurs. To analyze the occurrence of catenary arc, the established pantograph system model is calculated. The results show that the maximum electric field outside the contact line occurs on the arc directly below the contact line, and the electric field is symmetrically distributed with respect to the contact line. The electric field variation cloud map from 0 ms to 70 ms is shown in Figure 11. The area covered by the arc becomes larger as the arc occurrence increases within a certain period, and the dynamic change during occurrence of the catenary arc shows the significant difference.

When the catenary arc occurs, the cathode electrons move from the skateboard to the contact wire anode and the anode surface current density increases, gradually increasing the arc current density of the pantograph from the sliding plate to the contact wire, as shown in Figure 12.

The current density of the catenary arc decreases gradually from the center area to the periphery. The closer to the anode area, more obvious the contraction of the arc column. The current density gradually increases and the maximum value in the anode area could reach 2.72 × 10⁷ A·m⁻².

The change frequency of the power frequency electric field is relatively low around the mobile catenary working position when it is powered on [30]. It belongs to the quasi-static field, and the Coulomb electric field is much greater than induced electric field, i.e., Formula (5) is combined with ${\displaystyle \raisebox{1ex}{$\partial B$}\!\left/ \!\raisebox{-1ex}{$\partial t$}\right.}\approx 0$.

$$\left\{\begin{array}{c}\nabla \times E=0\\ E=-\nabla \phi \end{array}\right.$$

(10)

The governing equation of the time-varying electromagnetic field is Maxwell’s equations, and the electric field is decoupled from the magnetic field. When the electric field is considered only, the simulated calculation results of the catenary arc current density are taken as the excitation sources of the electric field simulation model of the mobile catenary, and Formula (4) is replaced by the current continuity equation to obtain the governing equation of the quasi-static electric field as:

$$\nabla ·\left(J+{\displaystyle \frac{\partial D}{\partial t}}\right)=0$$

(11)

In Formula (11), $J=\sigma E$, $D=\epsilon E$, then there is:

$$-\nabla ·\left(\sigma \nabla \mathsf{\phi }\right)-\nabla ·\left(\epsilon \nabla {\displaystyle \frac{\partial \phi }{\partial t}}\right)=0$$

(12)

In the finite element software, the built model is entered to observe the output data and revise the model parameters based on actual situations. Then, the mathematical model is revised and perfected to evaluate the electric field distribution of the mobile catenary model, with results shown in Figure 13.

Observed from Figure 13, the maximum value of the electric field intensity is found at the contact line, i.e., 8156 V/m. Figure 14 shows the comparison of simulation and experiment results at the height of 6.0 m above the ground.

As shown in Figure 13 and Figure 14, the electric field intensity is distributed symmetrically, and it shows the obvious downward trend as the distance from the contact line increases. The spatial distribution and attenuation characteristics in the simulation results are basically consistent with the experimental results. To further verify the reliability of the established model, the horizontal section at the height of 1.5 m is selected in the geometric model to calculate the electric field intensity of the plane, with results shown in Figure 15.

It could be found from Figure 15 that the horizontal component of the electric field intensity at the height of 1.5 m is symmetrically distributed with respect to the contact line. The maximum value occurs at 1.8 m horizontally on both sides directly below the contact line at approximately 151 V/m, and it is mostly dense in the electric field lines. The comparison of horizonal simulation and experimental results of the electric field at the height of 1.5 m is shown in Figure 16.

The test environment is complex and it is close to the ground, so the data measurement is prone to the impact of carriage, cargo warehouse, and loading and unloading equipment. Although there are some differences between two curves, the sound consistency is observed. The simulation results basically match the experimental results, verifying the correctness and effectiveness of the model.

4. Conclusions

Taking the sunken mobile catenary of new equipment as the example, the electromagnetic environment is studied via experiment and simulation to establish the catenary arc model and contact line model. The proposed model could be applied to other railway transport routes by simply revising relevant parameters, which provides a certain basis for electromagnetic environment assessment. Experimental and simulation results indicate the following:

• The horizontal and vertical components of the electric field intensity are symmetrical and the electric field near the ground is mainly determined by the vertical component. The peak of electric field intensity near the ground is about 1.1 KV/m, which does not exceed the control limit of the power frequency electric field intensity (4 KV/m). The safety coefficient is greater than 50 V, with sufficient safety.
• The peak of the magnetic induction intensity occurs directly below the contact line, and it drops rapidly outside the wire through measurement. The magnetic induction intensity near the ground is on the order of 10⁻² MT and the maximum value is 0.03 MT, which does not exceed the exposure reference limit stipulated in ICNIRP, which proves that personnel are safe to work in this electromagnetic environment. The maximum value of the magnetic induction intensity near the contact line (6 m above the ground) could reach 0.35 MT, and it belongs to the hazardous zone.
• The electric field intensity measured increases by about 110 V/m and the magnetic induction intensity increases by about 0.004 MT under the self-weight load, wind load, and ice load. There is little difference in field strength, and the curves basically coincide under two loading conditions, which is slightly different directly under the contact line, proving that there is a certain normal operating capacity for the sunken mobile catenary under the complex environment.
• The spatial distribution and attenuation characteristics of the electric field in the simulation results are basically consistent with the experimental results, verifying the correctness and reliability of the model. The experiment and simulation results prove that the electric field in the freight area meets the requirements of environmental evaluation when the mobile catenary is in the working position.
• Further research should be conducted on the factors influencing the electromagnetic environment of the mobile catenary system, including materials, structural parameters, and operational status. Additionally, optimization strategies should be proposed to enhance the comprehensiveness and reliability of the conclusions.

The models proposed could be applied to other mobile catenary systems, and effectively solve the difficult and costly experimental measurement by modifying the traction network and other relevant parameters. It is conducive to provide a useful reference for railway engineering construction in the future, prevent the potential safety hazards that may occur during the loading and unloading of railway freight, and improve the adaptability and safety of the mobile catenary system under the complex electromagnetic environment. The conclusion proves that the sunken mobile catenary does not exceed the exposure limit of power frequency electromagnetic field when it runs, and it could greatly improve the organizational efficiency of railway freight, while guaranteeing the safety of personnel and equipment. The installation of mobile catenary in the freight loading and unloading stations of electrified railways addresses the reliance on diesel locomotives under fixed catenary systems, significantly reducing carbon emissions and associated environmental pollution. As a safe and reliable tool for sustainability, the mobile catenary system enhances the overall sustainability of electrified railway operations.