In mine power supply systems, high-voltage supply lines typically utilize armored cables; consequently, their failure rate is significantly lower than that of the cables used for low-voltage power supply. Power supply to mining districts constitutes a vulnerable link within the overall power system, and given the harsh working environment, the proper selection of cable types and cross-sections is critical to ensuring the safety of power supply operations. The following sections outline the methods for selecting cable types and determining cable cross-sections.
Selection of Cable Types
The selection of cable types is closely linked to the reliability and safety of the power supply, as well as its economic feasibility. Article 467 of the *Coal Mine Safety Regulations* establishes the following requirements for cable selection:
1. The actual vertical elevation difference at the cable installation site must be compatible with the maximum permissible vertical elevation difference specified for the selected cable.
2. Cables must incorporate a conductor of sufficient cross-section to serve as a protective earth ground.
3. The use of aluminum-sheathed cables is strictly prohibited.
4. It is mandatory to select flame-retardant cables that have passed inspection and obtained the "Safety Mark for Coal Mine Products."
5. The cross-section of the cable's main cores must be sufficient to meet the load requirements of the power supply line.
6. Requirements for fixed-installation high-voltage cables:
(1) In vertical shafts or roadways with an inclination angle of 45° or greater, PVC-insulated, coarse-steel-wire armored, PVC-sheathed power cables-or XLPE-insulated, coarse-steel-wire armored, PVC-sheathed power cables-shall be used.
(2) In horizontal roadways or roadways with an inclination angle of less than 45°, PVC-insulated, steel-tape or fine-steel-wire armored, PVC-sheathed power cables-or XLPE-insulated, steel-tape or fine-steel-wire armored, PVC-sheathed power cables-shall be used.
(3) Aluminum-core cables may be used in intake inclined shafts, shaft bottom stations and their immediate vicinity, and for connections between the central substation and mining district substations; in all other locations, copper-core cables must be used.
(4) For fixed-installation low-voltage cables, armored or non-armored "Mw" series cables-or flexible rubber-sheathed cables of the corresponding voltage rating-shall be used. (5) Non-fixed high- and low-voltage cables must be flexible rubber-sheathed cables that comply with the Mr818 standard. Mobile and handheld electrical equipment shall utilize specialized rubber-sheathed cables.
(6) Cables used for lighting, communication, signaling, and control purposes shall be armored communication cables, rubber-sheathed cables, or M-, Chang-, or Chang-type plastic-insulated power cables.
(7) Low-voltage cables should not utilize aluminum cores; within mining areas, the use of aluminum-core low-voltage cables is strictly prohibited.
Selection of Cable Cross-Sections
The selection of cable cross-sections encompasses both high-voltage and low-voltage cables, with the selection of low-voltage cable cross-sections serving as the primary focus.
1. Selection of Main Cable Cores
Generally, low-voltage power supply lines within mining areas are relatively long; during operation, the current flowing through the cables generates a voltage drop and causes heating. To ensure the proper functioning of both the cables and the motors, the following four principles must be observed when selecting cable cross-sections:
(1) During normal operation, the actual temperature rise of the cable shall not exceed the maximum temperature rise permissible for its insulation material.
(2) Selection shall be based on the permissible voltage drop allowed for the cable circuit during operation.
(3) The selected cable cross-section must satisfy the requirements for mechanical strength.
Mining cables refer to the wires and cable products utilized for both surface and underground equipment within the coal mining industry. These include cables for coal cutters, conveyors, communication systems, lighting, and signaling equipment, as well as cables for electric drills, cap lamps, and power supply cables for underground mobile substations.
