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Mine Power Substation

Mine Power Substation - The area containing electrical switchgear (circuit breakers, fuses, switches, and/or transformers), used for the purpose of controlling power from the surface power system to the underground mine power transmission.

  1. Alternating current installations shall include A through M.
    1. Access to the mine power substation area shall be restricted by a protective fence or building, unless pad-mounted equipment is used.
      1. Gates in the fence shall be bonded by shunt straps.
      2. Each continuous section of conductive fence, gate, and/or barbed wire shall be connected to the station ground grid.
      3. Fence sections and gate shall be a minimum of seven feet high above ground, or six feet high with one foot of suitable barbed wire.
      4. The station ground bed shall extend a minimum of three feet beyond the fence and gate swing radius.
      5. When the incoming power distribution includes a static wire that is available on the last pole outside the substation, the static wire shall be connected to the substation ground grid.
      6. The substation ground grid shall be tested and shown to be 4 ohms or less before the static wire is connected. All future tests shall be done with the static wire connected and the results documented.
      7. Pad-mounted electrical equipment that is totally enclosed, locked, and no exposed energized conductors need not be enclosed by a fence. Access shall only be available from outside the enclosure panels in accordance with IEEE standards for pad-mounted equipment.
    2. Properly rated primary or incoming lightning arrestors based on phase to phase voltage of system.
    3. Positive disconnecting means on the incoming or primary line with a circuit breaker or fuses to interrupt safely any current, normal or abnormal, which might be encountered shall be installed.
    4. Transformer bank to convert the incoming or primary voltage to the transmission voltage. Voltage regulating autotransformers may be used to regulate the mine transmission voltage, but may not be used to convert the incoming or primary voltage to the mine transmission voltage. The potential of the mine high -voltage transmission system will be maintained so that it does not exceed by more than 15% the high-voltage rating of any system component.
      1. Secondary or underground transmission voltage shall not exceed fifteen thousand volts, nominal, phase-to-phase.
      2. Connections to provide mine transmission voltage
        1. Delta-Wye, Wye-Delta, and Delta-Delta are permitted connections
        2. No Wye-Wye connections or autotransformers shall be utilized for this purpose.
      3. Transformers feeding power to surface loads must be installed within the Mine Power Substation ground grid if their source of power is tapped from the underground mine power transmission. These transformers must be of the two-winding type to provide ground circuit isolation.
      4. Where the substation primary or supply voltage is equal to the mine transmission voltage, the main transformer may be omitted and a zigzag transformer used to derive a system neutral, if the neutral is not otherwise available. Under this condition, the supply voltage must be a dedicated circuit for the mine power substation.
      5. Neutral points
        1. Zigzag or grounding transformers may be utilized on delta-connected secondaries for deriving the neutral for the four-wire transmission circuit.
        2. The zigzag or grounding transformer shall be of sufficient capacity to carry maximum ground fault current continuously.
    5. Properly rated secondary lightning arrestors based on the phase-to-phase voltage of the system.
    6. Ground fault current limiting resistor shall be:
      1. Capable of continuously limiting ground fault current to fifty amperes or less.
      2. Adequately insulated for phase-to-phase voltage.
      3. Properly protected by grounded fence or screen, unless mounted eight feet or more above ground.
      4. Located as close as possible to source transformer.
    7. Secondary or mine feeder circuit breaker with:
      1. Adequate interrupting capacity for any possible condition of fault and no less than the short circuit capacity of the system supplying power to the breaker.
      2. Positive disconnect means that shall be provided on the input and output sides of the breaker.
      3. Use of automatic reclosing circuit breakers is prohibited.
      4. Automatic tripping of circuit breakers by protective relays and shall provide as a minimum tripping by:
        1. Undervoltage: The undervoltage protection shall cause the undervoltage tripping solenoid to directly activate the circuit breaker tripping mechanism when the power circuit voltage is no less than 40% of nominal. Either of the following methods may be used to comply with this requirement:
          1. An undervoltage protective relay shall cause the undervoltage solenoid to directly activate the circuit breaker tripping mechanism when the power circuit voltage is no less than 40% of nominal. The undervoltage protective relay must be identified on the schematic and wiring diagrams. The identified relay may also serve another protective or control function.
          2. The solenoid may serve as both the undervoltage protective relay and the undervoltage tripping solenoid, if the solenoid directly causes the circuit breaker to trip when the power circuit voltage is no less than 40% of nominal.
        2. Instantaneous phase overcurrent relays on all three phases
        3. Inverse time limit phase overcurrent relays on all three phases
        4. Ground fault current not exceeding fifteen amperes
        5. Ground-continuity check not exceeding seven amperes
        6. Ground fault-current limiting resistor protection and monitoring by current and potential transformer relaying.
      5. Ground-continuity check circuit that shall continuously monitor the integrity of the neutral circuit leading underground and shall cause breaker to open when either the ground or pilot check wire is broken.
      6. An ammeter capable of reading current in each phase and a voltmeter capable of reading phase-to-phase voltage shall be provided on all three phases at the circuit breaker.
      7. If any of the required protective relays operate only the shunt trip, then a shunt trip supervisory circuit is necessary.
      8. The open or closed status of the circuit breaker shall be indicated.
    8. Surge protection or station ground bed shall be maintained at four ohms or less.
      1. Connected to all lightning arrestors, substation equipment frames, fence or enclosures (if metallic) and substation structures (if metallic).
      2. There shall be no direct connection between this ground bed and either the grounded side of the mine direct current system or the neutral ground bed.
    9. Neutral or primary ground bed maintained at four ohms or less.
      1. Located at least twenty-five feet away from any station ground at its closest point. Only the inby or load end of the neutral current limiting resistor shall be connected to this ground bed. This connection shall be made by a conductor insulated for the phase to phase voltage of the system.
      2. No direct or metallic connection between any point of the high voltage alternating current neutral circuit and the mine direct current ground.
    10. High voltage conductors or cables leading underground from the mine power substation shall be flame resistant type and adequate for the intended current and voltage.
    11. Generators may be used as a power source.
      1. Located on a ground grid connected to the station ground grid.
      2. Transfer switches between the permanent mine power source and a generator shall not be made or broken under load, unless properly rated to interrupt available fault current.
      3. Input and output connections shall be hardwired.
    12. Enclosures shall be appropriately labeled for function and voltage.
    13. Checklist of required information for mine power substations (to be shown on schematics):
      1. One-line diagram of complete substation.
      2. All neutral and station groundbeds and fence/gate (or enclosure) layouts.
      3. All power and ground conductor sizes and insulation ratings.
      4. Transformer voltages, KVA, impedance, winding configuration and tap specifications
      5. Zig-zag transformer voltage and current ratings.
      6. Lightning arrestor voltage ratings.
      7. Disconnect switch voltage and current ratings.
      8. Circuit breaker or fuse voltage and current ratings and interrupting ratings.
      9. Ground fault current limiting resistor voltage and current rating.
      10. Generator voltage, KW, and available fault current.
      11. Control circuit schematic.