Abstract: A semi-conductor system for controlling three phase motors by voltage and/or frequency variations. An input circuit provides dc power, such as a three phase full wave input bridge with silicon control rectifiers to provide a voltage controlled dc power output. An output inverter bridge having six silicon rectifiers receives dc power and converts it to three phase ac power for operating an induction motor. A diverter network is connected between the dc power input circuit and the output inverter and is activated periodically for temporarily diverting the dc power from the inverter in order that the inverter rectifiers may be turned off. The diverter may include a tank circuit having a capacitor and an inductor connected across the dc power output through a diode and a silicon control rectifier is connected to the tank circuit for shunting the dc power from the inverter and applying a reverse voltage to the inverter.

Abstract: A method and apparatus to control delivery of pressurized hydraulic fluid at a controlled pressure to open and close blowout preventers. A source of pressurized hydraulic fluid is connected through a pair of supply lines and through a control shifter valve for charging a closed system to a set-point pressure. A velocity fuse in each supply line diverts flow to one line if the other line breaks. Fluid from the source of pressurized hydraulic fluid is also delivered through a regulator valve to a regulated pressure line which is connected to one or more control valves. Each of the control valves is adapted to direct pressurized fluid selectively to either end of a blowout preventer actuator chamber.