Simulation and Finite Element Analysis of the Electrical Contact Characteristics of Closing Resistors Under Dynamic Closing Impacts

Abstract

Closing resistors in ultra-high-voltage (UHV) gas-insulated circuit breakers (GCBs) are critical components designed to suppress inrush currents and transient overvoltages during switching operations. However, in practical service, these resistors are subjected to repeated mechanical impacts and transient electrical stresses, leading to degradation of their electrical contact interfaces, fluctuating resistance values, and potential failure of the entire breaker assembly. Existing studies mostly simplify the closing resistor as a constant resistance element, neglecting the coupled electro-thermal–mechanical effects that occur during transient events. In this work, a comprehensive modeling framework is developed to investigate the dynamic electrical contact characteristics of a 750 kV GCB closing resistor under transient closing impacts. First, an electromagnetic transient model is built to calculate the combined inrush and power-frequency currents flowing through the resistor during its pre-insertion period. A full-scale mechanical test platform is then used to capture acceleration signals representing the mechanical shock imparted to the resistor stack. These measured signals are fed into a finite element model incorporating the Cooper–Mikic–Yovanovich (CMY) electrical contact correlation to simulate stress evolution, current density distribution, and temperature rise at the resistor interface. The simulation reveals pronounced skin effect and current crowding at resistor edges, leading to localized heating, while transient mechanical impacts cause contact pressure to fluctuate dynamically—resulting in a temporary decrease and subsequent recovery of contact resistance. These findings provide insight into the real-time behavior of closing resistors under operational conditions and offer a theoretical basis for design optimization and lifetime assessment of UHV GCBs.

1. Introduction

Closing resistors are widely installed in ultra- and extra-high-voltage (UHV/EHV) circuit breakers to mitigate transient phenomena during switching operations. By temporarily inserting a high-value resistance into the circuit prior to main contact closure, the resistor absorbs part of the system’s energy, reduces electromagnetic oscillations, and suppresses inrush currents and overvoltages [1,2,3,4]. Despite their crucial function, closing resistors are mechanically and thermally vulnerable. Frequent operations of GCBs subject the resistor stack to repetitive mechanical shocks from the operating mechanism, as well as sudden transient current surges, leading to cumulative wear, contact degradation, and even catastrophic failures [5,6,7,8]. In several documented incidents at converter stations, resistor-related failures have caused breaker misoperation and large-scale outages [9,10,11,12,13].

Previous research has primarily focused on electromagnetic transient analysis, often modeling the closing resistor as a fixed-value element to study its effect on inrush currents, overvoltages, and optimal insertion angles [14,15,16,17,18,19,20,21,22,23,24]. While these studies have provided valuable insights for system-level behavior, they largely overlook the microscale dynamic phenomena at the resistor contact interface—namely, the interplay of mechanical impact, electrical current, and thermal stress that causes the resistor’s resistance to fluctuate during operation.

In reality, the resistor plates are assembled with spring-loaded pressure and feature rough metallic surfaces. Contact occurs only at discrete microscopic asperities, forming a network of constriction points where current is funneled through, creating constriction resistance and film resistance. Under transient impacts, the contact pressure varies, the constriction spots expand or collapse, and the effective resistance evolves dynamically. This transient resistance behavior has important implications for heat generation, skin-effect-driven current distribution, and the overall lifetime of the resistor assembly.

To address this gap, this paper investigates the dynamic electrical contact characteristics of a 750 kV GCB closing resistor under real operating conditions. A combined methodology is adopted:

(1)

a system-level electromagnetic transient model is built to compute the current waveform through the resistor during its 10 ms pre-insertion interval;

(2)

a mechanical test platform for a full-scale GCB captures acceleration signals representing operational impact;

(3)

these inputs feed into a finite element (FE) model incorporating the Cooper–Mikic–Yovanovich (CMY) correlation to calculate contact resistance, stress evolution, and temperature rise under coupled electro-thermal–mechanical conditions.

(4)

a parametric study is performed based on the validated FE model to quantify the impacts of preload force failure and surface wear on the thermal performance and to evaluate the effectiveness of edge chamfering in optimizing current distribution.

The results not only quantify the dynamic resistance variation caused by transient mechanical shocks and thermal expansion but also provide a framework and specific design insights for resistor design optimization, edge current mitigation strategies (e.g., chamfering), failure mechanism analysis, and long-term reliability assessment for UHV GCBs in power systems.

2. Methodology

2.1. Electrical Contact Theory

The machined surface of a solid material is never perfectly smooth; instead, it consists of numerous microscopic asperities of varying height and size. As a result, when two solid surfaces are pressed together, the real contact occurs only at discrete spots rather than over the entire apparent (nominal) contact area. In electrical contact theory, the nominal contact area refers to the geometrical overlap of two surfaces, while the real contact area is composed of a collection of microscopic contact spots.

Due to the presence of oxide layers, corrosion films, and contamination on the surface, not all asperity contacts are electrically active. Only those metallic junctions that pierce through the contaminant layer, or those that involve a conductive film, can carry current effectively. These microscopic conduction sites are called conductive spots or a-spots [25], as illustrated in Figure 1.

When current flows through such a surface, it is constricted through these tiny α-spots. This current constriction causes the effective conduction area to be reduced and the current path to lengthen, thereby producing an additional localized resistance, known as constriction resistance. Furthermore, if a contamination or oxide film exists on the surface, an additional film resistance is introduced. Figure 2 illustrates how the current lines converge at a conductive spot.

The contact resistance can be expressed by the following formula:

$$R_{\mathrm{C}}={\displaystyle \frac{{\mathsf{\rho }}_1+{\mathsf{\rho }}_2}{4a}}={\displaystyle \frac{{\mathsf{\rho }}^{*}}{2a}}$$

(1)

$$R_{\mathrm{C}}={\displaystyle \frac{{\mathsf{\rho }}_{\mathrm{F}}d}{\mathrm{\pi }{a}^2}}$$

(2)

$$R_{\mathrm{J}}=R_{\mathrm{C}}+R_{\mathrm{F}}$$

(3)

where R_C is the contraction resistance, a is the radius of the circular conductive spot, ρ₁ and ρ₂ are the resistivity of the contact material, and ρ* is the equivalent resistivity; R_F is the membrane resistance, ρ_F is the membrane resistivity, d is the membrane thickness, and R_J is the contact resistance.

Contact resistance is the dominant contributor to the temperature rise at an electrical interface. For finite element (FE) simulations, the Cooper–Mikic–Yovanovich (CMY) correlation model [26] is widely adopted to represent this theory, enabling the calculation of constriction resistance and thermal constriction conductance:

$$h_{\mathrm{c}}=1.25{\sigma }_{\mathrm{contact}}{\displaystyle \frac{m_{\mathrm{asp}}}{{\sigma }_{\mathrm{asp}}}}{\left({\displaystyle \frac{p_{\mathrm{c}}}{H_{\mathrm{c}}}}\right)}^{0.95}$$

(4)

$${\sigma }_{\mathrm{contact}}={\displaystyle \frac{2{\sigma }_{\mathrm{u}}{\sigma }_{\mathrm{d}}}{{\sigma }_{\mathrm{u}}+{\sigma }_{\mathrm{d}}}},k_{\mathrm{contact}}={\displaystyle \frac{2k_{\mathrm{u}}{k}_{\mathrm{d}}}{k_{\mathrm{u}}+k_{\mathrm{d}}}}$$

(5)

$${\sigma }_{\mathrm{asp}}=\sqrt{{\sigma }_{\mathrm{asp},\mathrm{u}}^2+{\sigma }_{\mathrm{asp},\mathrm{d}}^2},m_{\mathrm{asp}}=\sqrt{m_{\mathrm{asp},\mathrm{u}}^2+m_{\mathrm{asp},\mathrm{d}}^2}$$

(6)

where h_c is the constriction conductance (S/m); σ_contact is the harmonic mean electrical conductivity of the mating surfaces, k_contact is the harmonic mean thermal conductivity, σ_asp is the combined surface roughness, and m_asp is the mean surface slope.

Table 1. Genetic algorithm parameter settings table.

Physical Quantity	Parameter Description
Hc	Contact material hardness
pc	Contact pressure
σu, σd	Conductivity of upper and lower contact materials
ku, kd	Thermal conductivity of upper and lower contact materials
σasp,u, σasp,d	Average roughness of the upper and lower contact surfaces
masp,u, masp,d	Average slope of upper and lower contact surfaces

lists the physical parameters used in the model.

Because the current density is highly concentrated at the α-spots, substantial localized heating occurs. The heat generation at each contact spot is proportional to the square of the local current density. The interfacial temperature rise can be calculated using Kohlrausch’s equation [27]:

$$U_C^2=8{\int }_{T_0}^{T_M}z\left(T\right)o\left(T\right)\mathrm{d}T$$

(7)

where U_C is the voltage drop across the contact system; T₀ is the reference temperature measurement; and T_M is the temperature on the contact plane. Kohlrausch demonstrated that, under specified conditions, every equipotential surface is also an isothermal surface, which describes the relationship between temperature and potential on these equipotential/isothermal surfaces within a conductor. In the contact fingers, a thermally symmetric characteristic contact state can be assumed, from which the temperature T at the contact point can be expressed as:

$$T=\sqrt{{\displaystyle \frac{U_C^2}{4L}}+T_1^2}$$

(8)

where L is the Lorenz coefficient. For metals that comply with the Wiedemann–Franz–Lorenz law, such as copper and silver, L takes a value of 2.4 × 10⁻⁸ (V/K)²; and T₁ is the conductor temperature.

2.2. Current Flow Through Closing Resistor

2.2.1. Simulation Model

This study focuses on the AC side of a 750 kV system. Therefore, the simulation model is powered by an AC source representing an infinite bus corresponding to the system short-circuit capacity. The simplified system consists of the circuit breaker, AC filters, shunt capacitor banks, and surge arresters; converter transformers and DC components are excluded to speed up computation while maintaining accuracy. A schematic of the model is shown in Figure 3.

The AC filters in the converter station can be classified into three categories: single-tuned (or low-frequency) filters BP11/BP13 and HP3; double-tuned filters HP11/13 and HP24/36; and shunt capacitors (SC).

A review of the continuous operating voltage of the surge arresters reveals that the arrester for the single-tuned filter (HP3) has the highest continuous operating voltage, which determines its reference voltage. In contrast, the surge arresters for the double-tuned filters (HP11/13) and shunt capacitors have lower continuous operating voltages, and their reference voltage is determined by the requirement for arrester operation during normal AC filter operation.

In addition, shunt capacitors (SC) are used to provide reactive power compensation. The detailed structure is shown in Figure 4, where C₁ and C₂ are capacitors, L₁ and L₂ are inductors, R₁ and R₂ are resistors, and F₁ and F₂ are surge arresters. The parameters of each filter component are listed in

Table 2. Parameters of each filter element.

Element	Filter Grouping Type
	BP11/BP13	HP24/36	HP3	SC
C1, μF	0.705/0.707	1.421	1.4227	1.745
L1, mH	118.096/84.783	8.598	445.11	2
C2, μF	-	8.266	11.3816
L2, mH	-	1.362
R1, Ω	12,000/12,000	300	2237.4

.

The system uses a single-phase, double-break SF₆ circuit breaker with a pre-insertion resistor (PIR), as illustrated in Figure 5. The PIR is connected in parallel with the main interrupter. When the circuit breaker receives a closing command from the system, the operating mechanism drives both the main and auxiliary contacts to close simultaneously. During closing, the resistor contact engages 8–10 ms earlier than the main contact, temporarily inserting the resistor into the circuit. In this phase, the PIR limits closing overvoltages and inrush currents. Once the main contact fully closes, it short-circuits the PIR, which is then withdrawn from operation.

During opening, when the circuit breaker receives an opening command, the auxiliary contact opens first under the action of a damping spring, followed by the main contact, interrupting the current and preparing for the next closing operation. In other words, the auxiliary contact follows the following sequence: closes first during closing and opens first during opening.

In this system, the PIR has a resistance value of 1500 Ω and a pre-insertion duration of 10 ms.

2.2.2. Random Closing

Simulation results (Figure 6) indicate that among the four filter branches, the shunt capacitor experiences the largest inrush current when the breaker closes, with a peak of 3.36 kA and slow decay. This high inrush current arises because the capacitive branch has a very low inductive reactance, resulting in a low equivalent impedance at the instant of closing, which allows a substantial transient current.

Unlike previous studies that focus mainly on the main contact current, this study examines the current through the closing resistor during its pre-insertion period. After 10 ms, the main contacts bypass the resistor, but during this brief interval, the resistor experiences a combination of impulse current and power-frequency current (Figure 7).

2.3. Processing of Operational Shock Signals

When the closing resistor engages during breaker operation, it is inserted 8–11 ms prior to main contact closure. During this period, the resistor plates are subjected to mechanical vibration caused by the operating mechanism, as well as thermal stress generated by the current-induced heating. This implies that the contact pressure between resistor plates becomes a time-dependent variable, directly influencing the dynamic contact resistance and temperature.

To investigate this phenomenon, an experimental platform was built using a full-scale LW55C-800 GCB (Henan Pinggao Electric Co., Ltd., Pingdingshan, China), with a dual-break, parallel-type closing resistor. Measurement points were carefully selected to capture the vibration characteristics of the resistor stack during operation. The interrupter chamber was mounted in the main tank, with all cables routed through a sealed feedthrough. Acceleration signals were collected via sensors connected to a data acquisition card, which interfaced with a computer terminal (Figure 8).

The breaker’s operating mechanism has a simple force transmission path to enable fast switching. However, the mechanical action involves collisions and friction, producing significant vibration. Dynamic and static contacts collide during operation, and vibration signals overlap and decay. Because the operating mechanism moves at high speed, the vibration acceleration can reach hundreds of g (g = 9.8 m/s²). A typical time-domain waveform of the vibration signal during closing is shown in Figure 9. At the same time, the time-domain signal characteristic curve of the vibration acceleration for the first 20 ms at the moment of contact between the moving and stationary contacts of the circuit breaker is taken as an interpolation function and input into the model.

3. Results and Discussions

3.1. Model Construction

A finite element (FE) model of the closing resistor stack was developed to capture the coupled electrical–thermal–mechanical response under transient conditions. The material properties of the resistor plates are listed in

Table 3. Test transformer parameters.

Attribute	Value
Density (kg/m3)	2250
Conductivity (S/m)	2.6
Surface Conductivity (S/m)	3.77 × 107
Conductivity of paint layer (S/m)	1.03 × 10−12
Relative dielectric constant	5
Thermal conductivity	0.04
Constant pressure heat capacity (J/(kg K))	890
Young’s modulus (GPa)	30
Poisson’s ratio	0.28

. The contact surface of the resistor is made of aluminum oxide, and the outer edge is coated with insulating paint, so its surface conductivity and paint layer conductivity differ from the bulk conductivity. In the model, it is defined in the material model in the form of a boundary.

The maximum element size was set to 0.762 mm, while a local refinement was applied to the critical contact boundaries and regions with anticipated high gradients, achieving a minimum element size of 0.00152 mm to ensure sufficient resolution of the localized physical fields, as shown in Figure 10.

The pre-insertion resistor experiences a temperature rise under the coupled effects of electromagnetic, thermal, and mechanical fields, as illustrated in Figure 11. In the electrical field analysis, the model accounts for the temperature-dependent variation of material resistivity, the skin effect, and the impact of contact resistance influenced by mechanical pressure, while the proximity effect is neglected. In the thermal field, Joule heat generation and pressure-dependent contact thermal resistance are considered, whereas eddy current losses caused by magnetic effects are ignored since the resistor materials are non-magnetic and the induced eddy currents are negligible compared to the conduction current. In the mechanical field, both thermal stress and the external loads (spring preload and contact constraints) are included.

The fields are strongly coupled: the electrical field affects the thermal field by determining Joule heat generation, while the thermal field, in turn, influences the electrical field by altering the temperature-dependent resistivity of the materials. Similarly, thermal stress alters material deformation in the mechanical field, thereby modifying the contact pressure between resistor plates. This contact pressure subsequently impacts both contact thermal resistance and contact electrical resistance. Hence, the electrical and thermal fields are bidirectionally coupled, as are the thermal and mechanical fields, while the mechanical field is unidirectionally coupled to the electrical field.

The governing equation for the spring base and resistor plate contact constraint (formulated using the Augmented Lagrangian Method) is expressed as:

$$F_{\mathrm{spring}}=k_{\mathrm{eff}}(u_0+{\lambda }_{\mathrm{n}})+p_{\mathrm{n}}+{ϵ}_{\mathrm{n}}{g}_{\mathrm{n}}$$

(9)

where F_spring is the spring force, k_eff is the effective spring stiffness, and u₀ represents the pre-compression displacement determined by the initial spring preload. λ_n is the Lagrange multiplier, and p_n denotes the normal pressure per unit area at the contact interface, describing the degree of compression between the resistor plate surfaces. ϵ_n is the penalty parameter, and g_n represents the normal gap distance.

Two main parameters govern the electrical conductivity at the interfaces between plates: contact pressure and surface roughness. Using the LW13-800 (Henan Pinggao Electric Co., Ltd., Pingdingshan, China) type gas-insulated circuit breaker as an example, the assembly of the resistor stack relies on the compression force provided by springs. When compressed to the specified dimension, the spring exerts a force of 4964 N, which corresponds to an initial assembly pressure of 192 kPa on each resistor plate interface.

Surface roughness measurements were also performed on the resistor plates. The maximum peak-to-valley height along the surface contour was 35.8 μm, and the arithmetic average roughness was 3.4039 μm. These measurements were incorporated into the FE model to more accurately reflect the initial contact state.

3.2. Simulation Results and Analysis

The total current through the pre-insertion resistor (PIR) under closing conditions—obtained by superimposing the transient surge current and the power-frequency current calculated in Section 2—was applied to the finite element (FE) model, together with the acceleration profile corresponding to the mechanical closing shock and the initial spring preload stress at both ends of the resistor stack. These inputs served as boundary and loading conditions for the simulation, enabling a comprehensive evaluation of the stress distribution, current conduction characteristics, and temperature rise behavior of the PIR under realistic closing conditions.

Under the influence of transient surge current, the skin effect becomes evident, leading to a significant concentration of current density along the resistor plate edges. At approximately 10 ms, the PIR experienced its peak through-current of 3285.5 A, with the maximum edge current density reaching 202.22 kA/m², as shown in Figure 12. This nonuniform current distribution amplifies localized Joule heating at the contact regions, particularly at microscopic asperities where the true conductive spots are located.

Following the transient surge event, the temperature of the resistor plates rose noticeably. Compared to the ambient temperature of 293.15 K, the bulk plate temperature reached a peak of 324.83 K, while the contact interface maximum temperature climbed even higher, peaking at 544.21 K—still below the allowable limit of 600 K for the resistor material (Figure 13). These findings indicate that although the PIR operates within its thermal capacity, localized hotspots could contribute to long-term degradation of contact integrity if subjected to frequent switching operations.

Due to the aluminum foil shims used between the resistor plates as connecting layers, the thermal stress generated during heating can be partially released. During the transient current surge, thermal expansion causes the resistor plates to displace under the action of the compression mechanism, reducing the contact stress. However, as the temperature of the plates continues to rise, the expansion becomes constrained by the spring force, generating additional compressive stress. Consequently, the contact stress of the resistor plates recovers. After the transient current surge subsides and the temperature stabilizes, the resistor plates cease expanding, and the contact pressure between them increases to 395.88 kPa. At the same time, the equivalent resistance of the closing resistor plates varies with the contact stress, further influencing the surface contact resistance. This leads to the observed resistance drop–recovery phenomenon during switching: initially, improved contact characteristics lower the total resistance; after the transient current event, the electrical stress decreases, the spring compression adjusts to a new equilibrium point, contact quality slightly deteriorates, and the total resistance rises again, as shown in Figure 14a.

The simulation results reveal that stress concentration is most pronounced at the lower edge of the resistor stack, where the maximum compressive stress reached 189.36 kPa, as shown in Figure 14b. This localized concentration of stress is consistent with previously reported findings, confirming that the FE model accurately reflects the actual operating state of the PIR.

The equivalent resistance of the pre-insertion resistor (PIR) exhibits a dynamic response closely coupled to the evolution of contact stress between the stacked resistor plates. As the contact pressure fluctuates, it directly modulates the microscopic contact resistance at the interface. Consequently, the PIR demonstrates a distinct resistance drop–rebound phenomenon during the closing and opening sequence. Initially, under the onset of through-current, the microscopic contact conditions improve due to localized asperity deformation, resulting in a reduction of the overall resistance. However, as the transient current surge subsides, the associated electro-mechanical stress relaxes, altering the compression state of the spring assembly. This shift establishes a new mechanical equilibrium, where the contact interface becomes slightly less conductive, leading to a gradual recovery of the total resistance to a higher steady-state value, as illustrated in Figure 15.

3.3. Parametric Influence Analysis

The closing resistor may undergo operational changes such as preload relaxation and surface wear during actual service, which significantly affect its thermal stability and electrical performance. To systematically evaluate the influence of key parameter variations, this section conducts a parametric study based on the validated finite element model, investigating three specific conditions: preload failure, increased surface roughness, and edge chamfering. The aim is to reveal the mechanisms of potential failure modes and provide a theoretical basis for optimized design.

3.3.1. Influence of Preload Force Failure

The stability of spring preload is critical for maintaining good electrical contact between resistive plates. In practice, preload force may decrease due to mechanical relaxation, thermal aging, or repeated operations. To quantify this effect, the preload force was set to 80% of its nominal value, simulating a typical preload degradation scenario. This threshold was selected with reference to engineering safety margins for preload force, aiming to evaluate the thermal stability of the system under non-ideal conditions.

As shown in Figure 16, after a 20% reduction in preload force, the maximum temperature in the contact region of the resistive plate reaches 628.43 K, significantly exceeding the allowable material temperature of 600 K. The increase in temperature is primarily attributed to the reduction in real contact area due to decreased contact pressure, leading to higher contact resistance and increased Joule heating losses. These results confirm that preload failure considerably increases the risk of thermal damage, highlighting the importance of regular maintenance and preload monitoring.

3.3.2. Influence of Surface Roughness Variation

The surface roughness of the resistive plates directly affects contact resistance and thermal conduction performance. Long-term operation involving arcing erosion, mechanical wear, and oxidation can significantly increase surface roughness. In this study, the roughness parameter was increased from an initial value of 3.4 μm to 7 μm to simulate a moderate level of surface wear. This value was selected based on statistical measurements of surface topography from resistors in actual service.

As shown in Figure 17, under increased roughness conditions, the maximum contact temperature rises to 587.20 K, approaching the allowable temperature limit. This is caused by a reduction in effective contact points due to increased roughness, which constricts current conduction paths, thereby increasing local current density and contact resistance. The results indicate that even with normal preload, surface wear can still be a critical factor limiting the thermal performance of the resistor, particularly under frequent operation and high-current conditions where the degradation of contact condition requires special attention.

3.3.3. Influence of Edge Chamfering

To mitigate current concentration at the edges caused by the skin effect, an optimization measure involving a 2 mm × 45° chamfer at the edges of the resistive plate was proposed. This design aims to improve current distribution by modifying the edge geometry to reduce local magnetic field intensity. Simulations were conducted under the same current conditions, preload, and vibration characteristics as the baseline model to independently evaluate the effect of chamfering.

The results show that the maximum current density at the edges of the chamfered structure is 183.25 kA/m², approximately 9.4% lower than that of the original structure (Figure 18a). Although the chamfer slightly reduces the apparent contact area, the improved current distribution significantly reduces the risk of local overheating, with the maximum temperature reaching 564.35 K (Figure 18b), which remains within the allowable limit. This demonstrates that edge chamfering is an effective and feasible design optimization measure that can significantly improve current distribution uniformity and thermal safety margin, even with a slight reduction in contact area.

4. Discussion and Conclusions

This study developed a comprehensive electro-thermo-mechanical coupling modeling framework to investigate the dynamic contact characteristics of a closing resistor in a 750 kV gas-insulated circuit breaker under transient closing conditions. By integrating system-level electromagnetic transient simulation, full-scale mechanical testing, and finite element analysis, the research provides new insights into the dynamic behavior of resistor stacks during switching operations. The main findings are summarized as follows:

(1)

The microscopic roughness of resistor plate surfaces results in a significantly reduced real contact area compared to the nominal cross-section, generating substantial constriction resistance and thermal resistance at the interfaces that lead to elevated localized temperatures.

(2)

The skin effect causes pronounced current concentration at plate edges during transient events, intensifying localized heating. Parametric studies demonstrate that edge chamfering (2 mm × 45°) effectively reduces current crowding by approximately 9.4%, offering a viable optimization strategy for current distribution improvement.

(3)

Both mechanical shock from the operating mechanism and thermal stress from Joule heating dynamically affect interfacial contact pressure. This interaction leads to a characteristic pressure drop followed by gradual recovery during switching events, significantly influencing the contact reliability.

(4)

Contact pressure variations directly modulate both contact resistance and bulk resistance, causing the overall resistance to exhibit a temporary decrease followed by rebound during the pre-insertion interval. Parametric analysis reveals that preload force reduction to 80% of nominal value elevates peak temperature to 628.43 K (exceeding the 600 K safety limit), while a surface roughness increase to 7 μm raises the temperature to 587.20 K (approaching the safety limit).

These findings provide valuable insights for the design and optimization of closing resistors in ultra-high-voltage circuit breakers. The results support improvements in material selection, surface finishing techniques, and structural design—particularly through edge optimization and preload force management—to ensure reliable operation and extended service life of switching equipment in high-stress environments. The developed modeling approach offers an effective tool for performance prediction and design evaluation of electrical contact systems in high-voltage applications.