The VariStroke-DX (dual-transfer) skid is a dual-redundant hydraulic servo system which enables uninterrupted operations through on-line servo repair and replacement. Woodward’s innovative design, qualification and manufacture combines the robust dirt-tolerant technology of its industry proven and reliable single-acting VariStroke GI servos into an API612 redundant stand-alone hydraulic skid. The master/slave control with fast transfer times minimize system disturbances in mechanical-drive or generator-drive steam turbines all while using a low-pressure hydraulic oil source (typically turbine lube oil) to provide its output shaft driving force.
Designed for extreme use environments, the VariStroke-DX includes isolation valves with lock-out/tag-out protection and convenient knife-switch electrical terminal blocks for ease of replacement. The dual-transfer skid design also includes on-line replaceable large pressure gauges to provide a complete serviceable package to delivers extended production without down-time for plant operators’ looking for longer production cycles and alignment with major overhaul periods in your specific application.
Applications:
API612 steam turbines driving
Critical for plant production and availability.
Designed as a stand-alone skid, servo-to-servo communication and automatic failover logic is included within each servo forcing automatic transfers to the healthy servo with no external control logic or interface required. Optionally, users can use a local switch or control driven relay connected to the skid to routinely select and switch servo functions as the master and as the slave.
Features:
- Hazardous Rating: Zone 1
- Fail Direction: Retract
- Hydraulic Pressure: 3.44 to 35 bar (50 to 500 psi)
- Transfer Logic: Automatic “Bumpless” (Master to Slave), Manual External Selection
- Input Power: Accepts Redundant Inputs at 24 Vdc (18-32 Vdc) Each
- Demand Inputs: Accepts Redundant 4-20 mA
- Power Cylinder: Accepts Redundant Position Signals
Benefits:
- Fully packaged hydraulic assembly which includes automatic and manual switchover capability. This skid’s automatic switchover logic greatly simplifies the overall turbine control design and lowers system cost as no external switching logic or related wiring is required (not true with competing products).
- Pressure gauges are integrated into this skid to assist operators with verification of servo valve operation and control.
- Integrated isolation valves allow operators to easily isolate each servo valve for repair, replacement, and calibration without affecting the controlling servo valve or turbine operation.
- Each servo valve includes a discrete output relay contact which can be used to remotely indicate which servo valve is in control of the steam control valve/rack. A closed relay contact indicates which servo valve is currently functioning as the master unit.
The VariStroke-DX skid is designed to be used in combination with Woodward’s single-acting VariStroke Hydraulic Power Cylinders (VHPC). Depending on the application, users can order and pair the correct size (bore, stroke length, return spring force, etc.) VHPC with the VariStroke-DX skid to meet their specific application’s requirements.
Application Notes
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