In 10kV distribution systems, cable terminations are one of the key components that directly affect system reliability.

As a protection device connected in parallel with the power system, a surge arrester remains energized for many years and continuously operates under electrical stress.

Compared with ordinary cable accessories, surge arresters require higher levels of insulation performance, sealing reliability, and long-term structural stability.

In recent years, rear plug-in surge arresters have gradually become a widely used solution.

By reserving a standard plug-in interface at the rear of the termination, the surge arrester can be directly connected to the termination.

This design eliminates external connection wires, additional brackets, and extra installation space.

However, one important point is often overlooked:

Rear plug-in is only an installation method. Behind the same rear plug-in design, different manufacturing processes can lead to significant differences in long-term reliability.

1. Assembly-Type Terminations: Internal Interfaces Are the Main Challenge

Traditional assembly-type rear plug-in surge arresters are manufactured by combining several separate components together.

The ZnO resistor blocks, insulation housing, semi-conductive shielding layer, sealing parts, and grounding components are produced separately and then assembled into a complete plug-in unit through assembly, encapsulation, and compression processes.

However, whenever multiple components are assembled together, internal interfaces inevitably exist.

And these interfaces may create potential risks, such as:

• Small air gaps; 
• Material separation; 
• Weak bonding areas between different layers. 

These issues may not always be visible during factory testing or at the early stage of operation.

Standard withstand voltage tests and partial discharge tests may not always detect very small defects inside the structure.

However, after years of operation under continuous electrical stress, these hidden weaknesses may gradually develop into reliability problems.

The possible failure process is:

1. Electric Field Disturbance Caused by Air Gaps

Air gaps inside insulation can disturb the electric field and create weak points where partial discharge may start.

2. Long-Term Damage Caused by Partial Discharge

Continuous partial discharge can gradually damage insulation materials and accelerate aging.

3. Interface Failure

Over time, discharge may continue developing along internal interfaces and eventually lead to insulation failure.

More importantly, the performance of assembly-type structures is highly dependent on installation quality.

Small differences in:

• Installation methods; 
• Surface cleanliness; 
• Silicone grease application; 
• Compression force; 

may affect the final consistency of the product.

In other words:

Assembly-type technology leaves some critical quality factors to the installation process, where control can be more difficult.

2. Integrated Molding Process: Removing Internal Interfaces from the Structure

The key idea behind an integrated molding process is simple:

Create a complete structure instead of assembling multiple separate parts.

In an integrated molded termination, the stress cone, main insulation, and external shielding layer are molded together in the same mold.

These components become a unified structure with improved consistency.

The surge arrester plug-in unit itself — including the ZnO resistor blocks, insulation layer, and external shielding layer — is also manufactured through an integrated molding process.

The plug-in unit and termination share:

• The same manufacturing process; 
• The same material system; 
• A continuous shielding structure. 

After installation, they form a stable shielding and sealing system.

When internal assembly interfaces are removed, problems related to interfaces, such as:

• Air gaps; 
• Internal separation; 
• Weak bonding areas; 

can be significantly reduced.

This is not simply an improvement of an existing process. It is a way to reduce potential problems from the structural design stage.

The value of an integrated molding process can be understood from three perspectives:

1. More Stable Electric Field Control

The geometric relationship between the stress cone and insulation layer is controlled by the mold.

This improves product consistency and reduces the influence of installation differences.

As a result, the electric field distribution becomes more stable.

2. Lower Partial Discharge Risk

A dense internal structure with fewer potential air gaps helps reduce the possibility of partial discharge.

During long-term energized operation, the risk of local discharge and hot spots can be effectively reduced.

3. Better Resistance to Aging and Environmental Stress

Under challenging conditions such as:

• Humidity; 
• Pollution; 
• Temperature changes; 

a structure with fewer internal interfaces provides better protection against moisture penetration and electrical stress.

The material and structure can maintain stable performance over a longer service period.

In simple terms:

The integrated molding process moves more quality control from the installation site back to the factory manufacturing process.

For power system operators, this means:

More consistent products and more predictable long-term performance.

3. Why Are Surge Arresters More Sensitive to Internal Interfaces?

For ordinary cable accessories, the impact of interface problems may be relatively limited.

However, surge arresters are different.

They have three characteristics that make manufacturing differences more important.

First, They Remain Energized Continuously and Generate Heat

Surge arresters are permanently connected in parallel with the power system.

They continuously withstand operating voltage, while a small leakage current flows through the ZnO resistor elements and generates heat.

It is similar to a small heater that operates continuously throughout its service life.

Under this condition, internal air gaps create two risks:

First, they may trigger partial discharge.

Second, they may create local hot spots due to different heat transfer characteristics.

The temperature increase can further increase leakage current, which causes more heat generation.

This creates a cycle:

Higher temperature → Faster aging → More heat generation

Second, Moisture Is One of the Biggest Threats, and It Often Enters Through Interfaces

One of the main causes of surge arrester failure is moisture penetration.

The failure process is usually:

Seal aging → Moisture ingress → Increased leakage current → Higher temperature → Performance degradation

In traditional assembly-type structures, internal interfaces can become potential paths for moisture.

Third, They Must Withstand Repeated Plugging and Unplugging

For assembly-type plug-in units, every installation and removal may affect the internal interface condition.

Over time, this may result in:

• Silicone grease loss; 
• Seal wear; 
• Reduced contact pressure. 

For integrated molded structures, shielding and sealing performance are mainly provided by the structure itself.

Even after repeated plugging operations, performance can remain more stable.

4. Comparison of Two Rear Plug-In Surge Arrester Solutions

5. Conclusion

Returning to the original question:

For the same rear plug-in surge arrester design, which manufacturing process provides better long-term performance?

When both solutions have the same installation method, protection requirements, and space advantages, the key difference comes down to one factor:

How the internal structure is manufactured and how potential weak points are controlled.

The value of an integrated molding process can be summarized in three aspects:

• Removing weak internal interfaces from the structure itself, improving long-term reliability; 
• Moving more quality control from the installation site back to the factory, improving product consistency; 
• Creating a sealing system that works together with the termination body, supporting a more balanced service life. 

In simple terms:

The value of integrated molding is not only about changing the manufacturing process. It is about reducing uncertainty throughout the entire product lifecycle.

One solution may focus more on initial cost, while the other focuses more on long-term reliability and lifecycle value.

For modern distribution networks pursuing:

• Higher reliability; 
• Lower maintenance; 
• More predictable operation; 

improving structural design and manufacturing consistency has become an important direction for the future development of cable accessories.