The CPC is an electrohydraulic pressure-regulating valve control that utilizes a very accurate internal pressure sensor and PID controller to precisely control steam turbine valves. The CPC consists of a valve-actuator assembly, pressure sensor, and electronic driver module. The unit’s driver module accepts one (or two) 4–20 mA pressure setpoints and compares these setpoints to the sensed oil pressure, to accurately control turbine valve oil pressure.
The CPC controls oil pressure by porting supply-oil to its control-oil output port (turbine valve control oil) or back to the system supply tank. This converter’s special PID architecture allows it to perform very stable pressure control during normal conditions, and respond in milliseconds to desired valve step changes during system or plant transients. As a means of protecting the turbine, an internal valve-return-spring forces the CPC to a failsafe position (port oil to drain) and safely close turbine control valves upon any internal unit failure (electrical input power failure, pressure sensor failure, processor failure, etc.).
The CPC is factory and/or field configurable via a computerbased service tool. The CPC’s PCI Service Tool uses a simple user-friendly format to allow users to easily configure, calibrate, and adjust all internal functions and PID control settings. The CPC includes a 4–20 mA output channel to indicate control oil pressure level, and unit alarm and shutdown relay outputs for use as unit health and status indications into the system controller or plant DCS.