Modelling a Challenging BESS Cable Installation Using Cableizer

As Battery Energy Storage System (BESS) projects continue to increase in scale, cable routing arrangements are becoming more complex. On a recent project, I was asked to assess a particularly challenging low voltage cable installation where conventional rating approaches would have introduced significant uncertainty.

The project involved multiple LV power cables installed within a series of ducts arranged in horizontal formation, located approximately 300 mm above an existing 33 kV cable system. The combination of congested cable routes, mutual heating effects, and the proximity of higher-voltage circuits created a scenario where detailed thermal modelling was essential.

The Challenge

Cable rating calculations are often straightforward when dealing with isolated cable circuits installed under standard conditions. However, BESS projects frequently introduce more demanding installation arrangements due to the high number of cables required within a relatively constrained footprint.

In this case, the installation included:

• Multiple LV circuits installed within individual ducts.

• Several ducts grouped together in horizontal formation.

• Close proximity to existing 33 kV cable circuits.

• Limited vertical separation between the LV and HV cable systems.

• A requirement to maximise cable utilisation while maintaining compliance with temperature limits.

The key concern was understanding how much thermal interaction would occur between:

1. Adjacent LV circuits.

2. Multiple ducts within the same installation corridor.

3. The LV duct bank and the underlying 33 kV cables.

Without detailed analysis, any cable selection would need to rely on conservative assumptions, potentially leading to unnecessary cable oversizing and increased project costs.

Why Cableizer Was Selected

For installations involving significant thermal interaction, analytical methods and standard correction factors can become increasingly difficult to apply with confidence.

Cableizer provides advanced thermal modelling capabilities that allow complex underground cable arrangements to be represented in detail. Rather than applying broad simplifications, the software can account for the actual installation geometry, cable spacing, duct arrangements, soil conditions, and circuit loading.

For this BESS project, Cableizer allowed the cable system to be built as a representative model of the final installation, providing a much clearer understanding of the thermal behaviour of the cable corridor.

Building the Model

The thermal model incorporated:

• Individual LV cable circuits.

• Duct dimensions and spacing.

• Horizontal duct bank configuration.

• Burial depths.

• Separation distances between circuits.

• The location of the underlying 33 kV cables.

• Soil thermal properties.

• Design loading conditions.

One of the important aspects of the assessment was ensuring that the influence of the 33 kV cables was properly understood. Although the vertical separation appeared reasonable at first glance, even relatively modest temperature rises from underlying circuits can affect the available thermal capacity of cables installed above them.

By incorporating both cable systems into the model, it became possible to quantify the impact rather than relying on assumptions.

Understanding the Results

The modelling demonstrated how heat generated by individual circuits interacted throughout the installation corridor.

Several observations became apparent:

Mutual Heating Matters

The thermal influence between adjacent LV circuits was significant. While a single circuit installed in isolation may have achieved a relatively high current rating, the grouped arrangement resulted in additional heating that needed to be accounted for.

Duct Arrangements Influence Capacity

The horizontal arrangement of multiple ducts created thermal overlap between circuits. The spacing between ducts became an important factor in determining overall cable performance.

Existing Infrastructure Cannot Be Ignored

The underlying 33 kV cables contributed additional heat into the surrounding soil. Although not necessarily the dominant factor, their effect was measurable and therefore needed to be considered during the design process.

Detailed Modelling Reduces Uncertainty

Perhaps the most valuable outcome was the ability to replace conservative assumptions with project-specific analysis. This provided confidence that cable sizing decisions were based on realistic installation conditions.

The Value of Thermal Modelling on BESS Projects

BESS developments often contain large numbers of LV and MV cables crossing relatively compact sites. As a result, thermal interactions that might be negligible on smaller projects can become major design considerations.

Detailed thermal modelling offers several benefits:

• Improved confidence in cable ratings.

• Reduced risk of overheating.

• Better utilisation of installed cable assets.

• Potential reductions in cable sizes and associated costs.

• Increased confidence during design reviews and stakeholder discussions.

In my experience, projects involving congested cable corridors are particularly well suited to advanced thermal analysis, especially where multiple voltage levels share the same route.

Conclusion

This BESS project highlighted the importance of understanding real-world installation conditions rather than relying solely on standard cable rating assumptions. The combination of multiple LV circuits within ducts, grouped duct formations, and the proximity of 33 kV cables created a challenging thermal environment that required detailed assessment.

Using Cableizer enabled the installation to be modelled in a way that reflected the actual site layout, providing a clear understanding of the thermal interactions within the cable corridor and supporting informed design decisions.

As BESS projects continue to grow in size and complexity, advanced thermal modelling is becoming an increasingly valuable tool for achieving safe, efficient, and cost-effective cable system designs.

Author: Matthew Kinsey
Cable Engineering Services

Specialising in cable system design, thermal rating assessments, ampacity studies, and independent cable design reviews for renewable energy, BESS, transmission, and distribution projects.