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| High-voltage longwall equipment |
Description of Problem
The demand for larger, more powerful mining equipment stimulated the need for increased voltages for coal mine face machinery. Higher-voltage equipment can supply more power without the need for larger, heavier portable cables. Special design, use, and maintenance precautions are needed to ensure an equivalent level of safety when high-voltage systems are used in permissible areas. Prior to passage of the Mine Safety and Health Administration's (MSHA) final rule for high-voltage longwall machines, the voltage limit for type-accepted permissible longwall machines was 1,000 V ac. Equipment operating above 1,000 V ac required a petition for modification. This entailed an approval examination for each high-voltage longwall machine deployed inby, which greatly slowed the industry penetration of this more productive mining equipment.
Research and Development Activities
NIOSH research showed that higher voltages for face equipment was feasible with appropriate precautions. Under one study, a 750-kVA explosion-proof load center was built that was used by MSHA's Approval and Certification Center as a test bed. It provided important information about large-scale, high-voltage, explosion-proof equipment. Another research study produced finite-element stress calculations and a material analysis, the results of which helped formulate the final rule.
R&D Outputs and Transfer Activities
Several NIOSH reports provided technical information to MSHA that was used to help formulate new regulations to allow the use of high-voltage longwall machines in coal mines. The information included the enclosure pressures developed during electrical arcing at up to 15 kV in methane-air atmospheres. Also included were recommendations for high-voltage electrical creepage and clearance distances, design criteria for explosion-proof enclosures, and permissibility hazard reduction. The final rule credits two separate NIOSH research reports that were used to help formulate its technical language.
Description of Intermediate Outcome
MSHA published its final rule for 30 CFR 18 and 75, "Electric Motor-Driven Mine Equipment and Accessories and High-Voltage Longwall Equipment Standards for Underground Coal Mines" on March 11, 2002 (Federal Register, Vol. 67, No. 47, March 11, 2002, Rules and Regulations, pp. 10972-11005): http://www.dol.gov/msha/regs/fedreg/final/2002004863.pdf. This final rule established MSHA's new mandatory electrical safety standards for the installation, use, and maintenance of high-voltage longwall mining systems used in underground coal mines. The final rule also included design approval requirements for high-voltage equipment operated in longwall face areas of underground mines. The new provisions allow the use of high-voltage longwall face equipment with enhanced protection from fire, explosion, and shock hazards without the need for a petition for modification. This regulation ensures an equivalent level of electrical safety and streamlines the approvals process.