Electronic Driver Module (PCB)

The printed circuit board (PCB) is mounted on top of the housing. The PCB

performs the following tasks:

 Power Supply

 Isolated Input and Outputs

 Dual Redundant Demand inputs

 Dual Redundant inputs for Final Cylinder Feedback

  Microprocessor based control

 Actuator H-Bridge Drive

 Current Limiting for Thermal Protection

 Advanced Diagnostics

 Discrete Outputs for Fault, Alarm and Shutdown Enunciation

The shield connections for the Analog Output (terminal #20), CAN1 (terminal

#23) and CAN2 (terminal #29) are through capacitors only as indicated in the

wiring section of this manual.

The power supply section performs the EMI filtering on the (18 to 32) V (dc) input

voltage and generates controlled voltages for several electronics sub-systems.

The power supply system is monitored for proper operation. If input voltage or

internal power systems are detected outside of allowable operating ranges, a

diagnostic alarm will be enunciated.

Servo Valve Actuator

The VS-I uses a rotary limited angle torque (LAT) actuator. The permanent

magnet rotor is directly coupled to the servo valve.

The position of the rotor is measured by a solid state integrated circuit on the

PCB which detects the orientation of the sensing magnet on the shaft. The

H-bridge drive is regulated by the microprocessor to precisely control the servo

valve position and maintain the cylinder stroke position demand.

A unique function of the software is a periodic, symmetrically opposed impulse

which flushes silt and debris from the servo valve without causing undue wear

called “Silt Buster”. At the interval and amplitude selected by the user, this

function provides a very rapid motion of the hydraulic valve allowing any silt to be

flushed to the drain passage. This motion is followed immediately by a step of

equal amplitude in the opposite direction. The opposing symmetry of the impulse

results in no net change in fluid volume to the controlled servo valve, and thus

does not interrupt the control of the turbine. This unique function provides a

higher degree of stability, reliability, and silt resistance.

If the unit detects any diagnostic shut down condition, or if the detected

diagnostic condition prevents reliable control, or if a loss of power occurs, the

servo valve return spring forces the valve to connect the appropriate control

pressure to drain causing the cylinder to move to the fail-safe position.

Rotary Servo Valve

The servo valve has four ports: Supply, two Control Ports, and Drain/Tank. With

the hydraulic valve in its middle position, all ports are blocked. As the valve

rotates, the supply is connected to a control port while simultaneously connecting

the drain to the other control port. The combined action of the servo position

controller and cylinder position controller modulate the power cylinder position as

necessary to match the input demand.

Additionally, the Remote Servo has an OVBD (Over Board Drain) port which is

permanently connected to drain. This port can (optionally) be connected to the

OVBD connection on Hydraulic Power Cylinder to drain any leakage pass the

primary rod seal.

A unique function of the software is a periodic, symmetrically opposed impulse

which flushes silt and debris from the servo valve without causing undue wear

called “Silt Buster”. At the interval and amplitude selected by the user, this

function provides a very rapid motion of the hydraulic valve allowing any silt to be

flushed to the drain passage. This motion is followed immediately by a step of

equal amplitude in the opposite direction. The opposing symmetry of the impulse

results in no net change in fluid volume to the controlled servo valve, and thus

does not interrupt the control of the turbine. This unique function provides a

higher degree of stability, reliability, and silt resistance.

The VariStroke-I Remote Servo Kit contains the same primary

components as Integrated version, This kit allows the Hydraulic Power Cylinder

to be mounted separately from the servo in applications where space is

constrained.

Hydraulic Power Cylinder

The simple and robust design of VS-I hydraulic cylinder (Figure 1-3) is capable of

consistent performance for extended periods in challenging environments.

Hydraulic cylinder is designed to operate in wide range of hydraulic pressures

and with high oil contamination. The actuation stroke range can be adjusted

precisely using PC service tool allowing the same actuator to accommodate a

variety of strokes.

The hydraulic power cylinder is designed to be field replaceable in turbine shut

down condition.

Valve Rack Linearization—Since flow-through single and staged inlet steam

valves tend to be non-linear throughout their flow range, turbine controls must be

de-tuned to compensate for instability or sluggish control points throughout this

range. As a way of allowing turbine control optimization, the VariStroke-I includes

an 11-point linearization table to allow turbine OEMs or users to compensate for

poor valve linearization by digitally linearizing the control-to-valve flow

relationship.

Side Load Capability—A common problem with turbine actuators is oil leaking

from their output shaft due to connection to valve rack linkages which have an

arc-type of motion. This motion results in side loading of the actuator shaft, and

after long periods may result in shaft-seal wear and resultant oil leakage.

Designed for a continuous side load of up to 10% of actuator output, the

VariStroke-I actuator incorporates a high-force precision bearing and triple-seal

technology on its output shaft to solve this typical application problem.

The VariStroke Actuator offers the following benefits to the user in comparison to

other electro-hydraulic actuators:

Dirt Tolerance—The VariStroke-I actuator is specifically designed for steam

turbine applications where turbine lube oil is also used to power the hydraulic

turbine control valve actuator(s). Steam turbine applications can be extremely

challenging for hydraulic control valve actuators as dirt, metal shavings, water,

and other contaminants (babbitt, ammonia, etc.) are common in such oil

systems. Also due to the high temperatures at which steam turbines operate,

turbine oil breakdown is common, resulting in the creation of a sludge-type

substance and the varnishing of internal system components. However, the

VariStroke-I actuator is designed to operate reliably within such challenging

applications. Its corrosion-resistant materials, single moving rotary valve, 222 N

(50 lbf) of chip shear force, and self-cleaning port design allow it to operate in

such applications without experiencing undesirable sticking or dragging.

The actuator’s output shaft position is controlled by a digital controller with an

internal rotary servo valve that ports supply oil to and from its power cylinder

piston. This actuator’s digital controller architecture allows it to perform stable

position control during normal conditions, and also respond quickly to desired

valve step changes during system or plant transients. The actuator output force

is generated only by oil pressure for double-acting power cylinder. For the spring

assist actuator output force is a combination of force from hydraulic pressure and

spring. Spring assist cylinder is still working as double acting actuator but it has a

spring installed inside the cylinder. Spring can be mounted either on the piston or

rod side and it generates force toward the fail safe position. There are 3 different

spring force categories for each cylinder diameter, except for 8” and 10” cylinder

bores which need 4 spring force categories to cover application needs. The

springs are rated at about ~1.5%, ~2.5%, ~5.5% and ~10.5% of stall force at 500

psi supply pressure.

Introduction

The VariStroke-I is a linear electro-hydraulic actuator that utilizes a double-acting

or spring-assist power cylinder with integrated electronic driver module, servo

valve, and redundant MLDTs (Magnetostrictive Linear Displacement Transducer)

– based position feedback sensors to precisely control steam turbine valves. The

actuator’s driver module accepts one or two (redundant) 4–20 mA demand

setpoints and compares these setpoints to the sensed actuator shaft position to

accurately control output shaft position.

The VariStroke-I is factory and/or field configurable via a computer-based service

tool. The actuator’s PCI Service Tool uses a simple user-friendly format to allow

users to easily configure, calibrate, and adjust all internal functions and response

settings. The VariStroke-I also includes a 4–20 mA output channel to indicate

output shaft (control valve) position, and unit alarm and shut down relay outputs

for use as unit health and status indications.

The total installed cost for this fully integrated actuator is low because it has been

completely assembled and tested at the factory. This greatly reduces OEM and

end-user fabrication time, testing time, and site assembly time.

Control Functions

Motor Start-up/Shutdown

The Vertex-Pro provides three selectable start-up modes—Manual, Semi-Auto, and Sequence. In the

manual mode, the throttle valve or inlet guide vane (IGV) is opened by an operator manually

raising/positioning the Vertex-Pro’s valve demand signal. In the semi-automatic mode, the valve/vanes

are automatically opened to the user-defined

position at a user-defined rate. In the sequence mode, the Vertex-Pro automatically controls valve

position based on a defined sequence in order to prevent a motor overcurrent condition.

Motor Current Limit Control

When configured, this control function senses motor current and limits compressor load to protect

against motor overload conditions.

Anti-Surge Control

The anti-surge PID uses compressor pressure, temperature, and flow signals to calculate each compressor

stage’s operating point, then compares this value to the specific surge map and surge control line to

position the respective recycle valve, and hold the compressor away from surge.

INPUT SIGNALS:

Power Sources (Simplex or Redundant)

 AC/DC—Power Supply (88–132 Vac/47–63 Hz or 100–150 Vdc)

 HVAC—Power Supply (180–264 Vac/47–63 Hz)

Discrete Inputs (38)

Two discrete inputs are assigned pre-determined functions and thirty-six are configurable:

 Emergency Shutdown

 Reset

 Configurable Discrete Inputs (36)

Analog Inputs (24)

Five analog inputs are assigned pre-determined functions, and twenty-one are configurable:

 Compressor Flow Signal (4–20 mA)

 Compressor Suction Pressure Signal (4–20 mA)

 Compressor Discharge Pressure Signal (4–20 mA)

 Compressor Suction Temperature Signal (4–20 mA)

 Compressor Discharge Temperature Signal (4–20 mA)

 Configurable Analog Inputs (19) (4–20 mA)

OUTPUT SIGNALS:

Discrete Outputs (20)

Two discrete outputs are assigned pre-defined functions and, eighteen are configurable:

 Motor/Compressor Shutdown

 Motor/Compressor Alarm

 Configurable Discrete Outputs (18)

Analog Outputs (8)

One analog output is assigned pre-defined functions and seven are configurable:

 Anti-surge Valve (4–20 mA)

 Configurable Analog/Actuator Outputs (7) (4–20 mA)

Communication Ports (3)

 (2) Ethernet ports (OPC or Modbus® *)

 (1) Serial RS-232. RS-422. RS-485 Modbus port