Archives

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

Redundancy

With Vertex-Pro dual-redundant models, the CPU modules operate in a special master/slave

configuration, using synchronized memory and one-millisecond transfers to ensure bumpless transfers,

and allow on-line repairs, and program changes, to increase overall system availability. These models

allow for automatic and/or manual transfers between the two sets of modules in cases of external I/O,

internal module, or input power failures. Dual-redundant models allow any module to be replaced while

the unit is operating on-line. Annunciation of any control failure or transfer is provided through all

communication links and event logs.

Configurability

The following I/O list is utilized by Vertex-Pro models only. Vertex-Pro-C models are customized to the

specific application and may use the same, or more or less I/O signals, depending on the application.

Vertex-Pro inputs and outputs (I/O) are arranged into pre-defined and configurable groups. Pre-defined

I/O is fixed based on its use in all or most applications. Configurable I/O is selected based on the specific

needs of each application.

Applications

The Vertex-Pro anti-surge control is designed for industrial-sized axial or centrifugal compressors with 1

to 4 recycle loops. Standard off-the-shelf models are available and field configurable for 1 or 2 recycle

loop applications, while custom models are available for larger 3 or 4 recycle loop applications. This

controller includes specifically designed algorithms and logic to start, stop, control, and protect industrial

compressors driven by a stationary speed motors or variable-frequency drive motors. OEM-qualified

algorithms are used within the Vertex-Pro for straight-through, iso cooled, double-flow, single side-

stream, and back-to-back compressor applications.

Designed to replace CCC Series-3 and Series 3++ anti-surge controllers, the Vertex-Pro can be configured

to function like these controllers but uses two-times faster scan rates, improved surge anticipation logic,

and one integrated package for all control functions (anti-surge control loop 1. anti-surge control loop 2. 

performance control, and dual-redundant control).

The standard Vertex-Pro models (1 & 2 recycle loops) are field-configurable, allowing users to

configure/select the specific control algorithm required for the specific compressor loop and application.

Since 3–4 loop compressor applications tend to be complex, Vertex-Pro-C models (3 & 4 recycle loops)

are custom programmed by Woodward engineers, ensuring that the correct control and optimization

algorithms are used to meet the specific application requirements.

For critical applications requiring increased reliability and availability, users can order dual-redundant

control models, which have manual switch-over and automatic fail-over capabilities. These redundant

control models also allow users to replace/repair modules and perform program changes while the

compressor is operating on-line, thus greatly improving system availability.

The Vertex-Pro controller includes the following PID control & protection functions:

 Anti-Surge PID Control

 Rate PID Control

 Boost (open-loop backup line response)

 Surge Recovery

 Surge Minimum Position

 Start, Purge, Stop, Shutdown, & Zero Speed Sequencing Positions

 Alarm & Shutdown Logic

Alternatively, the following functions can be configured, depending on the application requirements:

Motor

 Current limit PID Control

 Start Sequence Logic

Compressor

 Throttle or Inlet Guide Vane Ramp Loading (motor protection)

 Performance Control (compressor suction or discharge pressure, flow, or external signal)

 Load Sharing (parallel compressors up to three trains)

The Vertex-Pro is built on Woodward’s field-proven MicroNet™ platform, and is available in simplex

or dual redundant models. All models utilize the MicroNet’s compact 8-slot chassis and

robust field termination modules. Simplex models include one of every module, while

dual-redundant models include two of every module, allowing users to perform both

bumpless on-line program changes and on-line module replacements.

The Vertex-Pro chassis is designed to be bulkhead-mounted in a cabinet or control

panel, and contains the required I/O and core control software to control industrial

motor-driven compressors. Typically, this controller is located in an enclosure that is

rated for the site-specific environment. Field termination modules (with integrated

circuit fuse protection) are included with this controller to allow users to easily land

and manage compressor and system interface wiring. The control also supplies

source power for associated sensors and I/O circuits.

This control is field-configurable, allowing users to easily configure the control to

application-specific requirements.

A menu-driven software program (Control Assistant) is provided with the control,

and when installed on any Windows based computer or laptop, serves as the human

interface to the control and or compressor.

This Control Assistant is used to configure, service, and optionally operate the control.

Optionally a touchscreen OpView™ panel is available for use as a local or remote

operator control panel. This OpView panel is comprised of a 307 mm (12.1”) touchscreen 

computer, and connects to the control via an Ethernet link.