The application of 2400 V to longwall face equipment

Operational and safety aspects of 2400 V longwall systems, as compared with 995 V systems, are presented. A 900 ft face width was chosen for the comparison, and typical longwall equipment, power requirements, and cable lengths were selected. The kVA rating of the power-center transformer was specified as 2500 kVA, with a 0.05-pu impedance and a resistance-to-reactance ratio of 4.0. Maximum fault currents were calculated for each system voltage, assuming a bolted three-phase fault and an infinite bus at the primary of the power-center transformer. Maximum fault currents and interrupting capabilities of circuit breakers at both utilization voltages were then compared. Typical cable sizes were specified for each system voltage, and their respective voltage regulations were calculated. Voltage drops and motor-torque reductions were also calculated and compared for conveyer-motor starting conditions. Better voltage regulation, improved motor torque, and decreased cable sizes are achieved with the higher voltage. Enhanced safety features collectively provide a safer electrical installation at 2400 V than presently required for 995 V systems.<>