Fire Resistant Railway Signalling Cable Design
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Solution Overview
Problem
Existing fire-resistant signalling cables for railways are bulky, heavy, and complex due to multiple protective layers, which increase the metal sheath diameter and reduce the reduction factor, making them expensive and difficult to manufacture, while failing to ensure conductor protection during fires.
Innovation Solution
A signalling cable design with a cable core comprising insulated conductors by a fire barrier and flame retardant LSZH polymer layer, a copper screen in direct contact with the core, and two LSZH polymer layers outside the copper screen, maintaining a low reduction factor and simple structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple protective layers are added around the cable core to achieve fire resistance and flame retardancy, then the cable's fire performance is improved, but the cable becomes bigger, heavier, and more complex to manufacture
Solution Approach 1:
The patent combines the fire barrier and flame retardant insulating layer into a single integrated insulating structure around each conductor. The fire barrier (mica tape) and LSZH polymer layer are applied together as combined insulation, reducing the number of separate protective layers while maintaining both fire resistance and flame retardancy properties.
Solution Approach 2:
The LSZH polymer layers serve multiple functions simultaneously: they provide flame retardancy, act as fire protection barriers, and serve as structural cable components. The copper screen provides both electromagnetic shielding and structural integrity. This multi-functionality reduces the need for separate dedicated fire protection layers.
2Reliability
If multiple protective layers are added around the cable core to achieve fire resistance, then the cable's fire performance is improved, but the cable becomes heavier
Solution Approach 1:
The fire protection is applied locally where most needed - directly around each conductor with the fire barrier and flame retardant insulating layer. This localized approach provides effective fire protection at the critical points without requiring heavy uniform protection throughout the entire cable structure.
3Reliability
If multiple protective layers are added around the cable core to achieve fire resistance, then the cable's fire performance is improved, but the metal sheath diameter increases and the reduction factor decreases
Solution Approach 1:
The fire barrier and flame retardant insulating layer are applied preliminarily and directly to the conductors before the copper screen is installed. This preliminary application of fire protection at the conductor level provides fire resistance without requiring additional outer layers that would increase the overall cable diameter and affect the reduction factor.
4Reliability
If multiple protective layers are added around the cable core to achieve fire resistance, then the cable's fire performance is improved, but the cable becomes more expensive and difficult to manufacture
Solution Approach 1:
The fire barrier and flame retardant insulating layer are combined into a single manufacturing step where both layers are applied together during cable production. This merging of layers reduces the number of separate manufacturing operations required, simplifying the production process while maintaining fire resistance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cable achieves fire resistance and flame retardancy according to international standards, maintains a low reduction factor, and ensures conductor protection during fires, while being lighter and less complex to manufacture.
Implementation Method 1
the electromagnetic fields resulting from the power supply voltage of the catenaries (typically 25 KV AC) induce current in the parallel laid signalling cables
Implementation Method 2
the cables are provided with a metallic shield. The protective effect of this shield is rated as 'reduction factor' (rf)
Implementation Method 3
each being insulated by a fire barrier and a flame retardant low smoke zero halogen polymeric insulating layer
Implementation Method 4
at least one flame retardant low smoke zero halogen polymeric sheath in radially outer position with respect to the copper screen
Data Source
Figure 1
AI summary
The present invention relates to a signalling cable (1) comprising: - a cable core (2) comprising: ∘ a plurality of electric conductors (3) each insulated by a fire barrier (3a) and a flame retardant low smoke zero halogen polymeric insulating layer (3b); ∘ a core wrap (5); - a metallic screen (7) surrounding and in direct contact with the cable core (2); - at least one flame retardant low smoke zero halogen polymeric sheath (8, 9) in radially outer position with respect to the metallic screen (7).