The selection of underground cables in coal mines is a key link in ensuring the safe and reliable operation of underground power systems, which requires comprehensive consideration of various factors such as usage environment, technical parameters, and safety regulations. The following are detailed principles and guidelines for selecting underground cables:

1、 Basic principles of selection

1. ‌Scene matching principle‌：

• Mobile devices such as coal mining machines and tunneling machines should prioritize rubber sheathed cables, with a focus on flexibility and wear resistance (bending radius 6-8 times the outer diameter of the cable). Equipment with electronic control systems should additionally choose shielded types (such as MYP and MYPT series)

• Fixed lines can be selected according to the laying method: armored cables (MVV22, MYJV22) can be buried or laid along tunnels, and unarmored cables (MVV) can be selected for conduit laying

• Targeted selection is required for high-risk environments: flame retardant and anti-static type should be selected for high gas mines, and waterproof rubber sheathed cables (MYPTJ series) should be selected for water inflow tunnels

2. ‌Technical parameter matching‌：

• The voltage level must be ≥ system voltage (e.g. 0.66/1.14kV cable for 1140V equipment, 6/10kV cable for 6kV system)

• The current carrying capacity should be calculated based on the equipment power, referring to the GB 50217 standard, to ensure that the cable current carrying capacity is ≥ 1.2 times the rated current of the equipment

• The number of cores and cross-section need to be adapted to the requirements: power cables commonly use 4-core (3 fire and 1 ground) or 5-core (3 fire and 1 zero and 1 ground), and the number of control cable cores is determined according to the number of signal circuits (4-61 cores)

3. ‌Safety compliance bottom line‌：

• All mining cables must have the 'MA' certification issued by the National Mining Product Safety Mark Center

• Need to verify the product testing report to confirm that the performance parameters such as flame retardancy, anti-static, and insulation meet the standards

• Priority should be given to selecting products from legitimate manufacturers to ensure that the production process meets the standards (such as conductor purity ≥ 99.95%, uniform insulation layer thickness without bubbles)

2、 Key selection factors

1. Environmental adaptability

• ‌temperatureThe underground temperature is always high, and the cable should have strong heat resistance (such as XLPE insulation with a temperature resistance of up to 90 ℃)

• ‌humidityThe underground humidity is high, and the cable sheath material needs to be moisture-proof and have UV resistance and oxidation resistance

• ‌corrosiveThere are corrosive gases or liquids present, and the cable sheath material needs to be resistant to chemical corrosion

• ‌mechanical damageThe underground space is narrow and the working environment is unstable, so the cable needs to have excellent flexibility and anti vibration performance

2. Voltage level selection

According to the Coal Mine Safety Regulations and Power Supply Design Specifications, the underground voltage levels are divided into:

• High voltage level: 10000V (main power supply from underground substation to mining area substation), 6000V (secondary high voltage distribution voltage used in some mines)

• Medium voltage level: 1140V (common voltage for large equipment in comprehensive mining face), 660V (main voltage for power equipment in mining area)

• Low voltage level: 380V (power supply for small fixed equipment), 127V (dedicated voltage for lighting and signal systems), 36V (safe voltage for handheld devices)

3. Mechanical performance requirements

• Tensile strength: Steel wire armored cables should be used for vertical shafts or steeply inclined tunnels

• Wear resistance: Choose wear-resistant materials for mobile device cables to reduce replacement frequency

• Compressive performance: Armored structure is selected for fixed lines to reduce the risk of mechanical damage

3、 Suggestions for selecting different application scenarios

1. Select by region

• ‌Vertical shafts or tunnels with an inclination angle of 45 ° or more: Adopt PVC insulated thick steel wire armored PVC sheathed power cable, cross-linked polyethylene insulated thick steel wire armored PVC sheathed power cable

• ‌Horizontal tunnels or shafts with an inclination angle below 45 °: Adopt PVC insulated steel strip or fine steel wire armored PVC sheathed power cable, cross-linked ethylene steel strip or fine steel wire armored PVC sheathed power cable

• ‌Inlet inclined shaft, shaft bottom parking lot and its vicinity, between the central substation and the mining area substationAluminum core cables can be used; Copper core cables must be used in other locations

2. Select by device

• ‌Mobile equipment such as coal mining machines and tunneling machinesChoose MY type (0.38/0.66kV) rubber sheathed cable with a current carrying capacity of ≤ 50A; or MCP type (1.9/3.3kV) oil resistant and tear resistant cable with a thickened sheath of ≥ 3mm

• ‌Fixed equipment such as conveyorsChoose MVV type unarmored cable (underground dry tunnel) or MVV22 type steel belt armored version (6/10kV)

• ‌lighting systemUsing 127V dedicated voltage cable, 36V is the safe extra low voltage (selv)

• ‌communication systemUsing MHYV communication cable, it has the characteristics of waterproof, explosion-proof, pressure resistant, and tensile resistant

4、 National standards and industry norms

1. ‌Safety performance specifications‌：

• GB 3836 series standards: specifies the explosion-proof requirements for cables in explosive environments of coal mines

• MT 818 standard: requires cables to have good flame retardant properties

• Low smoke and halogen-free requirements: control the amount of smoke, avoid halogenated materials, and reduce the release of harmful gases

2. ‌Electrical performance requirements‌：

• Insulation resistance, dielectric loss, withstand voltage and other indicators need to meet the standards

• Conductor material: Multiple strands of copper wire are commonly used to ensure high conductivity and flexibility

3. ‌Installation specifications‌：

• Cables must be suspended: In horizontal tunnels or shafts with an inclination angle below 30 °, cables should be suspended using cable hooks

• The suspension of power cables should have appropriate sag, consistent sag and height, and be hung neatly without crossing

• Cables should not be hung on wind and water pipelines, and should not be exposed to water or dripping

5、 Suggestions for selection process

1. ‌Clearly define the usage environmentAssess underground temperature, humidity, corrosiveness, mechanical damage risk, etc

2. ‌Determine technical parametersCalculate load current, determine voltage level, select number of cores and cross-section

3. ‌Select cable typeDetermine based on device mobility (fixed/mobile) and installation method (direct burial/pipe penetration/suspension)

4. ‌Verify security performanceCheck 'MA' certification, flame retardant rating, anti-static performance, etc

5. ‌Consider maintenance costsChoose durable materials to reduce replacement frequency and lower later maintenance costs from the source of selection

By following the above principles and guidelines, it is possible to scientifically and reasonably select cables suitable for different scenarios underground in coal mines, ensuring the safe and reliable operation of the power system.