High Temperature Cycling in Cable Systems (MV)

Modern power grids are becoming increasingly dynamic. The integration of renewable energy sources and fluctuating load patterns introduces new operational stress factors for medium-voltage cable systems.
One of the most critical of these factors is high temperature cycling: the repeated heating and cooling of cable infrastructure under variable electrical load.
Where traditional systems operated under relatively stable conditions, today’s grids are defined by continuous thermal variation. This development directly impacts the performance and long-term reliability of cable joints.

→ What is High Temperature Cycling?
→ Why it matters to modern Grids?
→ How thermal cycling affects cable systems
→ Limitations of conventional jointing systems
→ Evaluation and testing considerations
→ Research findings on high temperature cycling in MV grids
→ System level perspective
→ Towards future proof joint design and conclusions
→ Downloadable content and related links

What is High Temperature Cycling?

High temperature cycling refers to the repeated heating and cooling of cable systems caused by varying electrical loads.
Typical drivers include:

  • Intermittent energy generation such as solar and wind
  • Load variability in electrified industrial processes
  • Grid congestion and switching operations

The result is not a stable thermal condition, but a continuous cycle of temperature changes within the system.

high Temperature Cycling in Cable Systems day/night difference

Why It Matters in Modern Grids

Thermal cycling is no longer an incidental phenomenon. It has become a structural characteristic of modern energy systems.
This challenges:
• Traditional design assumptions
• Lifetime predictions
• Reliability expectations
As a result, components that performed well under stable conditions may behave differently under dynamic load profiles.
Want to know if you have a problem with Thermal Cycling in your networ, just contact our specialists.

How Thermal Cycling Affects Cable Systems

Thermal cycling introduces several interconnected effects within cable systems.
Material Behaviour
Different materials expand and contract in response to temperature changes.
Mechanical Stress
Repeated expansion and contraction lead to stress accumulation, particularly at material interfaces.
Insulation Performance
Over time, insulation properties may degrade, and voids can form within the system.
These processes are progressive and often not directly visible, but they significantly influence long-term performance.

Cooling is an important driver for High Temperature Cycling in Cable Systems

Limitations of Conventional Jointing Approaches

Many jointing technologies have been developed based on assumptions of:

  • Stable load conditions
  • Predictable system behaviour
  • Controlled installation environments

In modern grids, where thermal cycling is dominant, these assumptions are no longer fully valid.
As a result, real-world performance may deviate from expected lifetime models
If you want to know more about technology as basis for the development of cable Joints, please download our Comparison guide for Jointing Technology below

Evaluation and Testing Considerations

Conventional testing methods are often based on steady-state conditions or limited cycling scenarios.
For dynamic applications, more representative approaches include:
• Extended thermal cycling tests
• Combined electrical and mechanical stress testing
• Long-term ageing simulations
These methods better reflect actual operating conditions in modern grids.

Research Findings on High Temperature Cycling in Medium-Voltage Joints

Research increasingly shows that high temperature cycling is a structural reliability factor in medium-voltage networks

The layers to create joint make the material interfaces

Field Evidence

A Jicable study (2011), reported that a significant share of cable joint failures is linked to high current loads, particularly cyclic loads.
The dominant degradation mechanism is thermo-mechanical:

  • Conductor expansion generates internal mechanical forces
  • These forces can lead to unexpected failure behaviour

Laboratory Validation

The same study demonstrated that these failure mechanisms can be reproduced under controlled test conditions.
This confirms that degradation is not incidental but a predictable effect of cyclic loading.

Interface behaviour

Additional research (Sensors, 2020) examined pressure behaviour at interfaces within cable joints.
Findings include:

  • Measurable pressure variations during thermal cycling
  • Variations up to approximately 40%
  • No full recovery after cooling

These effects contribute to Void Formation, Weak Spot Development and Accelerated Ageing.

Key Insight

The main risk is not temperature alone, but the interaction between:

  • Thermal variation
  • Mechanical stress
  • Material interface behaviour

This interaction determines how cable joints degrade over time under dynamic load conditions

System-Level perspective

Thermal cycling should not be analysed at component level alone.
Relevant system-level factors include:

  • Cable design and construction
  • Installation environment
  • Load profile over time
  • Accessibility for maintenance

A system-oriented approach provides a more accurate view of long-term performance.

Towards Future-Proof Joint Design

The focus in cable joint design is shifting.

From:Peak temperature  >>>>>  Towards  >>>>>   Internal temperature distribution

This determines:

  • Thermal gradients
  • Mechanical stress levels
  • Degradation behaviour

The insulation concept therefore becomes a key design parameter rather than a secondary consideration. As seen before and validated during tests the LoviSil® insulation is a non hardening liquid insulation that distributes temperatures better and keeps the joints and its material on a substantial lower temperature.

Conclusion

Cable joint performance under high temperature cycling is not defined by temperature alone.
It depends on:

  • Thermal gradients
  • Internal stresses
  • Long-term material behaviour

Solutions that reduce heat accumulation and limit thermo-mechanical stress contribute directly to improved reliability.
In increasingly dynamic power grids, this positions thermal management within cable joints as a critical factor in system performance.
Selecting the appropriate jointing concept is therefore not just a component choice, but a design decision.

Downloadable Content

Download : Azhar, H. (2024).  Added Value for Fluid Insulation. Lovink-Enertech. 
Download : Compare jointing technologies for Medium Voltage

Related Pages

Some pages that are related to the importance of fluid insulated joints for the long term reliability of electricity grids.

Applications in Renewables Energy Grids
Joints for Waterlogged areas
Transition Cable Joints 
Ageing of PILC Cables
Lovisil® Silicon insulated MV Joints program