What is the Type (N)TSCGECECWÖU MT BM PLUS Cable?

The Type (N)TSCGECECWÖU MT BM PLUS represents a specialized evolution of mining cables engineered specifically for tunnel boring machine (TBM) reeling drum applications. The “BM” designation stands for “Boring Machine,” and the “PLUS” indicates enhanced features including integrated control conductors and a monitoring system not found in standard mining cables.

This advanced cable system serves dual purposes: delivering medium voltage power (3.6/6 to 12/20 kV) to TBM cutting heads and auxiliary equipment while simultaneously providing control circuits for machine automation and continuous monitoring of cable sheath integrity. The cable’s construction specifically addresses the demanding mechanical requirements of tunnel construction, including torsional stress from reeling operations, continuous flexing during boring cycles, and harsh underground environmental conditions.

Primary Application Environments:

Purpose and Specialized Applications

Designed for Modern Tunnel Construction

The MT BM PLUS cable addresses the complete electrical needs of modern mechanized tunneling projects where TBMs operate continuously for months or years, advancing through varied geological conditions while maintaining power, control, and monitoring systems. The integrated design eliminates the need for separate control and monitoring cables, simplifying cable management and reducing failure points.

Critical Application Areas:

1. Large-Diameter TBM Operations

• Metro and Railway Tunnels: TBMs with 6-15m diameter cutting heads requiring multi-megawatt power supply (typically 6/10 kV or 12/20 kV systems)
• Road Tunnel Construction: Highway and expressway tunnel boring with large-diameter machines operating in challenging geology
• Water Conveyance Tunnels: Long-distance water transfer tunnels using gripper or shield TBMs
• Utility Tunnels: Shared utility corridor construction in urban environments

2. Hard Rock TBM Systems

• Gripper TBMs: Open-type machines for hard rock conditions where gripper shoes provide reaction force
• Double Shield TBMs: Combined gripper and shield systems for variable geology
• Mountain Tunnel Excavation: High-pressure rock conditions requiring robust cable systems
• Mining Decline Development: Access tunnel construction in mining operations

3. Soft Ground Shield TBMs

• Slurry Shield TBMs: Pressurized face support systems in waterlogged ground
• Earth Pressure Balance (EPB) TBMs: Mixed face excavation in urban environments
• Subsea Tunnel Construction: Underwater tunnel boring requiring complete water resistance

4. Micro/Mini TBM Applications

• Utility Installation: Small diameter (1-3m) tunnels for pipes, cables, and services
• Sewage System Construction: Underground drainage tunnel excavation
• Communication Infrastructure: Fiber optic and telecommunications tunnel installation

Monitoring Conductor System:

The unique monitoring conductor – a copper wire screen installed over the inner sheath – provides continuous surveillance of cable sheath integrity:

• Early Fault Detection: Changes in monitoring conductor resistance indicate sheath damage before insulation compromise
• Location Identification: Time-domain reflectometry (TDR) on monitoring conductor pinpoints damage location
• Predictive Maintenance: Trending monitoring conductor parameters enables scheduled replacement before failure
• Safety Enhancement: Provides warning of cable degradation in inaccessible tunnel sections

Advanced Technical Characteristics

Multi-Function Cable System Performance:

Electrical Performance Specifications:

Thermal and Environmental Performance:

Mechanical Performance Data:

• Maximum Tensile Load: 15 N/mm² of total phase conductor cross-section – optimized for controlled reeling drum tension
• Minimum Bending Radius: Per VDE 0298 Part 3 – typically 15-20x cable diameter depending on reeling drum design
• Maximum Torsional Stress: ±25°/m – critical specification for drum winding/unwinding operations
• Reeling Cycle Life: Designed for minimum 10,000 cycles under normal operating conditions
• Crush Resistance: Enhanced construction withstands cable management system pressures

Advanced Material Structure – Multi-Function Design

1. Phase Conductors (Power Transmission)

2. Primary Insulation System

• Semiconductive Conductor Screen: Tape applied over tinned conductor eliminates air voids
• 3GI3 Quality Rubber Insulation: EPR-based compound per VDE 0207 Part 20 providing electrical insulation
• Inner Semiconductive Layer: Extruded simultaneously with insulation ensuring perfect bonding
• Outer Semiconductive Layer: Provides smooth interface for earth conductor contact

3. Protective Earth Conductors

4. Control Conductors (Unique to MT BM PLUS)

5. Central Filler

Semiconductive compound on textile polyester support positioned at cable center. Functions include:

• Maintains circular cable geometry during bending and twisting
• Fills voids preventing water accumulation in tunnel environment
• Provides mechanical cushioning for cores during reeling
• Contributes to overall cable flexibility

6. Core Assembly

Three insulated phase conductors with individual earth screens, plus three control conductors, are twisted together with optimized lay length. TNT (non-woven textile) tape is wound over the twisted assembly, providing:

• Separation layer allowing controlled core rotation during torsional stress
• Protection of individual cores during handling
• Water-wicking prevention (TNT blocks capillary action)
• Smooth surface for inner sheath application

7. Inner Sheath – Primary Protection Layer

8. Monitoring Conductor (Unique Feature)

How Monitoring Conductor Works:

• Baseline Establishment: At installation, monitoring conductor resistance is measured and recorded (typically <2Ω per km)
• Continuous Surveillance: Automated systems measure resistance periodically (every hour or continuously)
• Damage Detection: Outer sheath damage exposes monitoring conductor to ground, changing resistance
• Location Identification: TDR sends pulse down monitoring conductor, reflection from damage point indicates distance
• Trending Analysis: Gradual resistance changes indicate progressive degradation requiring investigation

9. Outer Sheath – Final Protection

Compliance with International Standards

Primary Certification Standards:

TBM Cable Specific Testing Requirements:

Tunnel Construction Standards:

• EN 60204-1: Safety of machinery – Electrical equipment of machines (applicable to TBM electrical systems)
• IEC 61439: Low-voltage switchgear and controlgear assemblies (for TBM power distribution)
• ISO 23647: Guidelines for restricting the emissions of tunnel boring machines (environmental compliance)
• Regional Mining Standards: Additional certifications available for specific jurisdictions

Safety Thresholds and Operating Limits

Critical Safety Parameters for TBM Operations:

Torsional Stress Management:

Control Conductor Safety:

• Voltage Isolation: Ensure control circuits are properly isolated from power conductors – minimum 5kV withstand voltage
• Circuit Protection: Install individual overcurrent protection for each control conductor
• Signal Integrity: Shield control conductors from power conductor EMI where critical for automation systems
• Polarity Identification: Clearly mark control conductor functions to prevent mis-wiring

Monitoring Conductor System Safety:

Reeling Drum Installation Safety:

• Drum Diameter Verification: Measure actual drum diameter at installation – must exceed minimum bending radius
• Flange Guards: Install proper flange guards to prevent cable escape during reeling
• Emergency Stop: Integrate drum motor with TBM emergency stop system
• Cable Tension Monitoring: Install load cells on critical installations to verify tension within limits
• Proximity Sensors: Implement sensors to detect cable overlap or improper winding

Installation Precautions and Best Practices

Pre-Installation Testing and Verification:

Reeling Drum Installation Guidelines:

1. Drum Specification Verification

• Minimum Drum Diameter: Calculate based on cable OD – typically 30-40x depending on application
• Flange Height: Minimum 1.5x cable OD to prevent cable escape
• Drum Width: Sufficient for maximum cable length plus 10% safety margin
• Level Wind Mechanism: Required for cables >50mm OD or lengths >500m

2. Cable Loading on Drum

3. TBM Installation

• Cable Routing: Plan route avoiding sharp edges, hot surfaces, and moving equipment
• Support Systems: Install cable supports every 3-5m preventing catenary sag
• Entry Point Protection: Use cable glands with strain relief at TBM entry point
• Termination Location: Position terminations in protected, accessible areas of TBM
• Control Conductor Routing: Route control conductors away from high-current power connections to minimize interference

Operational Monitoring and Maintenance:

Continuous Monitoring Systems:

• Monitoring Conductor Surveillance: Automated resistance measurement every reeling cycle or hourly minimum
• Cable Tension Monitoring: Load cells verify tension remains within safe limits during operation
• Reeling Cycle Counter: Track cumulative cycles approaching 10,000 cycle replacement threshold
• Temperature Monitoring: Infrared sensors on terminations and high-current sections
• Control Circuit Monitoring: Verify control signal integrity during operation

Periodic Inspection Schedule:

TBM-Specific Operational Precautions:

• Advance Rate Coordination: Coordinate TBM advance rate with cable management system capacity
• Emergency Procedures: Establish procedures for rapid cable isolation in emergency situations
• Backup Power: Consider redundant power supply for critical TBM functions during cable maintenance
• Communication Systems: Ensure communication systems independent of cable-mounted control conductors
• Dust Management: Implement dust suppression near cable and reeling systems to prevent contamination

Common Problems and Advanced Troubleshooting

TBM Cable-Specific Issues:

1. Torsional Stress Damage

Symptoms: Internal conductor damage not visible externally, intermittent faults, gradual insulation resistance decrease, control conductor failures.

Root Causes:

• Inadequate drum diameter causing excessive twist during winding
• Improper level-wind operation allowing cross-winding
• Excessive cable tension during reeling amplifying torsional stress
• Accumulated stress from repeated reeling beyond design cycles

Diagnosis and Solutions:

• Calculate actual torsional stress: measure cable rotation per meter of deployment
• Inspect drum installation for proper diameter and level-wind function
• Review reeling procedures with operators – ensure proper technique
• If stress exceeds ±25°/m, implement corrective measures:
  • Increase drum diameter
  • Install or repair level-wind mechanism
  • Reduce cable tension during winding
  • Replace damaged cable – internal damage cannot be repaired
• Implement monitoring system to track torsional exposure

2. Monitoring Conductor System Failures

Symptoms: Monitoring conductor open circuit (infinite resistance), erratic resistance readings, loss of fault location capability.

Common Causes:

• Mechanical damage to outer sheath exposing monitoring conductor to physical damage
• Poor termination of monitoring conductor during installation
• Corrosion of monitoring conductor at termination points
• Monitoring conductor breakage from excessive cable bending

Solutions:

• Verify monitoring conductor connections at both cable ends – common failure point
• Apply corrosion protection compound at terminations
• If monitoring conductor damaged mid-cable, section-by-section testing identifies location
• For critical installations, implement redundant monitoring systems
• Document monitoring conductor baseline and acceptance criteria clearly

3. Control Conductor Failures

Symptoms: TBM automation malfunctions, sensor signal loss, safety interlock failures, PLC communication errors.

Root Causes:

• Control conductor breakage from excessive bending or torsional stress
• Insulation failure between control conductors or to ground
• Termination failures at control panels
• EMI interference from power conductors affecting control signals
• Water ingress affecting control conductor insulation

Troubleshooting and Resolution:

• Test each control conductor individually for continuity and insulation resistance
• Verify proper control voltage at both ends during fault condition
• Check for EMI interference using oscilloscope on control circuits
• Inspect control conductor terminations – often overlooked compared to power terminations
• For intermittent faults, monitor during TBM operation to correlate with specific movements
• If control conductor damaged, may be possible to re-route control circuits through spare conductors if available

4. Reeling Drum Mechanical Issues

Symptoms: Uneven cable winding, cable escape from drum, excessive tension, noisy operation.

Causes:

• Level-wind mechanism failure or misalignment
• Drum shaft bearing wear causing wobble
• Motor speed control problems causing jerky winding
• Inadequate flange height allowing cable overflow
• Debris accumulation on drum surface

Solutions:

• Inspect and service level-wind mechanism – critical for proper operation
• Check drum bearings for wear and replace if necessary
• Verify motor drive system operating smoothly with controlled acceleration
• Clean drum surface regularly to prevent foreign material buildup
• If cable has escaped drum, carefully rewind ensuring proper layering restored

5. Insulation Resistance Degradation

Symptoms: Gradual decrease in insulation resistance over time, intermittent earth faults, increased leakage current.

Causes Specific to TBM Applications:

• Tunnel moisture and humidity affecting insulation over months of operation
• Contamination from tunnel dust (often conductive minerals) on cable surface
• Thermal cycling from varying tunnel temperatures causing insulation stress
• Mechanical fatigue from thousands of reeling cycles
• Chemical exposure from ground water, drilling fluids, or exhaust gases

Preventive Measures:

• Establish insulation resistance trending program – plot monthly values
• Clean cable surface periodically using approved solvents
• Implement environmental controls where possible (ventilation, humidity control)
• Plan cable replacement before insulation resistance reaches critical minimum
• For long tunnels (>5km), consider multiple cable sections with intermediate splices for easier replacement

6. Termination Failures in Harsh Tunnel Environment

Symptoms: Localized heating at terminations, flashover, connection resistance increase, complete termination failure.

Contributing Factors:

• Dust and moisture accumulation on termination surfaces
• Vibration from TBM operation loosening connection hardware
• Inadequate creepage distance in high-humidity tunnel environment
• Corrosion of connection hardware from tunnel atmosphere

Best Practices:

• Use sealed termination enclosures rated IP65 minimum for tunnel service
• Apply silicone grease to all connection surfaces before assembly
• Re-torque all connection hardware after initial 24-hour operation period
• Schedule termination inspection and cleaning quarterly minimum
• Install terminations in protected areas of TBM away from dust/water exposure where possible

Complete Technical Specifications

Available Configurations (6/10 kV Example):

Note: Specifications shown for 6/10 kV rating with “üL” monitoring conductor. Similar configurations available for 3.6/6 kV, 8.7/15 kV, and 12/20 kV ratings. Custom lengths up to 2500m available on special reels for long tunnel projects.

Technical Resources and Industry Standards

Standards Organizations:

• VDE Institute – German electrical standards, DIN VDE specifications for mining and TBM cables
• International Electrotechnical Commission – Global electrical standards
• CENELEC – European electrical standardization
• ITA-AITES – International Tunnelling and Underground Space Association

Tunnel Industry Resources:

• Tunnel Business Magazine – TBM technology and project updates
• Underground Construction Magazine – Tunneling methods and equipment
• World Tunnel Congress Proceedings – Latest research and case studies

Feichun Cable Global Network:

• Mining Cables Latin America – Cables para túneles y máquinas tuneladoras en proyectos mineros
• Reeling Cable Solutions – Complete range for mobile mining and port equipment
• Australian Mining Cables – TBM cables for Australian tunnel and mining projects
• Crane and Festoon Cables – Specialized cables for port machinery
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