Project Overview
This project is a new IDNO (Independent Distribution Network Operator) primary substation requiring a long-distance 33kV cable connection from the NGED network. The project involved two incoming 33kV feeds over a 6.1km route, supplying a new primary substation with 33/11kV transformers for an 11kV IDNO distribution network.
This was one of the longest single cable studies we've undertaken, requiring detailed ampacity analysis and comprehensive cable pulling calculations to ensure the design was not just electrically compliant, but practically constructable.
The Challenge
Long-distance HV cable routes present unique engineering challenges beyond standard cable sizing. The 6.1km route required:
- • Thermal derating: Multiple cables in close proximity create mutual heating effects that reduce ampacity
- • Installation feasibility: Cable pulling tensions and sidewall pressures must stay within limits at every bend and section
- • Joint location optimisation: Minimising joints while keeping pulling sections manageable
- • Cost vs performance trade-offs: Balancing cable size, duct configuration, and installation complexity
Initial assessments showed that standard cable sizes (630mm² and 800mm²) would not meet the thermal requirements, driving the need for detailed optimisation analysis.
Our Approach
We delivered a comprehensive cable study covering ampacity, installation feasibility, and fault level compliance.
Cable Ampacity Study
- • Base case ampacity calculation
- • Duct configuration optimisation
- • Spacing and depth analysis
- • Thermal resistivity assessment
- • Software cross-validation
Cable Pulling Analysis
- • Section-by-section tension calc
- • Sidewall pressure verification
- • Route bend analysis
- • Joint location optimisation
- • Maximum section length limits
Network Configuration
- • 2x 33kV incoming feeds from NGED
- • IDNO primary substation
- • 2x 33/11kV transformers
- • 11kV IDNO distribution network
- • Fault level withstand verification
Technical Highlights
6.1km Route
One of the longest single cable studies undertaken—requiring comprehensive analysis beyond standard approaches.
Route Optimisation
Pulling sections reduced from 23 to 13 through iterative design, simplifying installation significantly.
Software Validation
Results verified using both EasyCableSizing and Cableizer, ensuring calculation accuracy.
Final Selection
1000mm² Al cable in 225mm ducts at 300mm centres—optimised configuration for this route.
Key Metrics
Iterative Design Process
The final design evolved through multiple iterations:
- Initial assessment: 630mm² cable insufficient for thermal requirements
- Second iteration: 800mm² cable still marginal on ampacity
- Final design: 1000mm² Al with optimised duct configuration
- Route optimisation: Pulling sections reduced from 23 to 13
Results
The study provided a complete cable design that meets both electrical requirements and installation constraints. The reduced pulling section count significantly simplified the installation scope.
"Completed for an IDNO developer via Greencurrent Power Engineering"
Key Facts
- Project Type
- IDNO Primary
- Cable Route
- 6.1 km
- Voltage
- 33 kV
- Cable Size
- 1000mm² Al
- Pulling Sections
- 13 sections
- DNO
- NGED (upstream)
- Location
- West Midlands
- Completion
- 2025
- Status
- Complete
Need HV cable studies?
We deliver comprehensive cable sizing including pulling analysis for constructability.
Get Your Quote