Current through Register Vol. XLI, No. 50, December 13, 2024
Section 36-48-3 - High Voltage Protection3.1. The nominal voltage of power circuits shall not exceed 2,400 volts.3.2. The nominal voltage of the control circuits shall not exceed 120 volts.3.3. The ground-fault current shall be limited by a neutral grounding resistor to not more than 0.5 ampere. Current transformers used for the ground-fault protection shall be the single-window type and shall be installed to encircle all three-phase conductors.3.4. The trailing cable for the 2,400-volt continuous miner circuit shall be provided with instantaneous ground-fault protection set at not more than 0.125 ampere. The ground-fault protection device shall be equipped with an impedance measuring feature, "Look-Ahead" circuit, to guard against closing the circuit breaker on a circuit that has an existing ground-fault condition.3.5. The neutral grounding resistor shall be provided with backup ground fault protection that will de-energize the primary of the transformer if a ground fault occurs with the neutral grounding resistor open. This protection shall be set at 40% of the maximum voltage that could appear across the neutral grounding resistor during a ground fault. A time delay set at the lowest practical value that permits reliable coordination shall be permitted. The time delay shall not exceed 0.250 second.3.6. The neutral grounding resistor for the transformer supplying power to the 2,400-volt continuous miner shall be provided with thermal protection that will de-energize the incoming high-voltage circuit supplying power to the power center if the grounding resistor is subjected to a sustained ground-fault. The thermal protection shall operate at either 50 percent of the maximum temperature rise of the grounding resistor, or 1500 C (3020 F), whichever is less. The thermal protection shall not be dependent upon control power and may consist of a current transformer and overcurrent relay in the grounding resistor circuit.3.7. The trailing cable for the continuous miner shall be provided with instantaneous short-circuit protection set at no more than the setting specified in the continuous miner approval documentation or 75 percent of the minimum phase-to-phase short-circuit current available at the continuous miner, whichever is less.3.8. The short-circuit protective device shall contain no intentional time delay and shall be based on the maximum asymmetrical starting current or have a time delay of no more than 0.05 seconds and be based on the maximum symmetrical starting current. The time delay settings shall not exceed the settings specified in the approval documentation.3.9. Guarding made of grounded metal or nonconductive flame-resistant material shall be provided to minimize the possibility of miners contacting the high-voltage trailing cable and to protect the high-voltage trailing cable from damage. The high-voltage trailing cable shall be installed on well insulated insulators or guarded at the following locations: 3.9.a. The high-voltage trailing cable shall be guarded at the power center cable coupler for a distance of 10 feet.3.9.b. The high-voltage trailing cable shall be installed on well insulated insulators from the power center to the last open crosscut and shall be guarded at any location on the working section where it may be damaged by moving equipment. That portion of the trailing cable that is located in or inby the last open crosscut shall be hung when other equipment cables must cross the high-voltage trailing cable.3.9.c. The high-voltage trailing cable shall be provided with a guard that extends from the high-voltage miner cable entrance gland for a distance of a minimum of 10 feet.