Abstract: A trolley wire for conveying direct current power to an electrically powered vehicle in an underground mine is connected in series with a shunt to a power source. The current drawn by the trolley wire passes through a circuit breaker and the shunt. The shunt generates a voltage input signal proportional to the current drawn by the trolley wire. A solid state comparator device receives the input signal and compares it to a reference signal having a magnitude representing the maximum level of current permitted to flow through the conductor. If the reference signal exceeds the input signal, the comparator device supplies an output signal that oscillates between a positive and a negative voltage to a trip circuit. The output signal actuates the operating coil of the circuit breaker so that the circuit breaker contacts remain closed to permit current to flow through the shunt to the trolley wire.

Abstract: A pair of sensor assemblies that change in electrical resistance when exposed to a mixture of combustible gas are positioned at a selected location in a mine or on a piece of operating equipment and receive power for continuous operation from a regulated power source. Regulator devices maintain a preselected input signal to the sensor assemblies. When exposed to a mixture of combustible gas, the sensor assemblies generate output signals which are received by a comparator and switch assembly. If an output signal of a sensor assembly exceeds a preselected signal of the comparator associated therewith, an alarm signal is generated and an audible and visual alarm device is actuated to indicate the presence of a combustible mixture of gas in the mine atmosphere. A time delay mechanism is operable to interrupt the input signal to the sensor assemblies if the alarm signal continues longer than a preselected interval.

Abstract: A synchronous machine, operable as both a motor and a generator, is mounted on an electrically powered vehicle, such as a mine shuttle car, and includes a plurality of conductors having connections that are detachably engagable with receptacles of a stationary power bank. Engagement of the conductors with the receptacles supplies variable voltage alternating current power to the machine. The machine is drivingly connected to a flywheel on the vehicle and, operating as a motor, energizes the flywheel to store a preselected amount of mechanical energy. The electrical connection between the vehicle and the power bank is opened after the flywheel has been sufficiently charged. The stored energy in the flywheel is then available to drive the machine as a generator and produce high frequency, three phase, alternating current power.