Modernisation of Control and Actuating Systems on Steam Turbines

Dipl.-Ing. Roland Schilling, Engineer Fritz Hofmann

Special Print from VGB PowerTech 3/2005

Kurzfassung

Modernisierungsalternativen für Stell-und Regeltechnik an Dampfturbinen

Leistungsfähige Stell- und Regelkomponentenzum Regeln der Dampfmassenströme beiDampfturbinen sind nicht nur bei Neuanlagenvorteilhaft. Eine Modernisierung der mecha-nisch hydraulischen Regelung bei bestehen-den Anlagen löst Probleme bei der Ersatzteil-beschaffung und bringt eine Verbesserungdes Regelverhaltens.

Je nach Zustand der bisherigen Stelltechnikstehen verschiedene Alternativen zur Verfü-gung. Häufig werden Druckstellglieder in dasvorhandene Regelölsystem eingebunden. Da-mit werden Stromeingangssignale in einenproportionalen Ausgangsdruck gewandelt.

Für verfügbarkeitskritische Applikationen gibtes auch redundante Ausführungen von Druck-stellgliedern.

Muss die Ansteuerung von einfach oder dop-pelt wirkenden Hydraulikzylindern ersetzt wer-den, kann ein elektrisch steuerbares Wege-schieberventil die richtige Lösung sein. Wege-schieber wandeln ein Stromeingangssignal ineinen proportionalen Hub.

Wenn es sinnvoll ist, den Hydraulikzylinderzu ersetzen, können Servomotoren eingesetztwerden. Servomotoren sind kompakte elektro-hydraulische Funktionseinheiten mit Positions-regler, Mengensteller und einem Hydraulik-zylinder. Diese Einheiten sind komplett geprüftund werkseitig eingestellt. Servomotoren sindfür verschiedene Anwendungen verfügbar,z. B. für eine Pilotventilverstellung, Ventilgrup-penverstellung oder Einzelventilantrieb.

An das Turbinenregelsystem werden je nachvorhandenem bzw. gewünschtem Automati-sierungsgrad unterschiedliche Anforderungengestellt. Neben den ursprünglichen Drehzahl-und Druckregelungen an einer Dampfturbineübernehmen Turbinenregelsysteme häufig eineReihe weiterer Funktionen.

Von einer modernen Turbinenleittechnik wirdhoher Bedienkomfort, benutzerorientierte Dar-stellung und Archivierung von Daten sowieeine mögliche Fehlerdiagnose erwartet.

Gemeinsam mit dem Betreiber kann die wirt-schaftlich und technisch sinnvollste Lösunggefunden werden.

Introduction

The control and actuating system is of greatimportance for the complete functioning of aturbine system. The customer expects high-quality technology at a favourable price.

Exact actuating components are necessary toadjust live and extraction steam valves.

Today’s digital turbine control systems offerhigh operating convenience, user-orienteddata presentation and filing as well as possi-ble remote diagnosis.

Motives to modernise the control and actuat-ing system:

— simplified, more rational handling,

— unavailability of spare parts,

— additional monitoring functions for tur-bine,

— creation of interconnected operation withother steam turbines of the plant,

— integration of turbine control and actuat-ing system in existing local process con-trol system,

— improvement of control behaviour.

— extension of turbine service life by tem-perature-dependent start-up programmes.

Electro-hydraulic Actuation

Depending on the condition of the former ac-tuating system various alternatives are avail-able.

I /H Conve r t e r s

I/H converters quickly and accurately convertan input signal 0/4 – 20 mA into a propor-tional output pressure.

Application

Triggering of pilot drives of positioningcylinders to control turbo machinery.

Design

I/H converters consist of a power-controlledsolenoid and a hydraulic unit ( F i g u r e 1 ).

Function

A 24V direct current activates a solenoid,which, in turn, generates power on the arma-ture via tappet. The power is specified via aninput signal of 0/4 – 20 mA.

Any modification of the 0/4 – 20 mA inputsignal affects the power generated by the so-lenoid onto the tappet.

This power is in balance with a hydraulicforce resulting from the output pressure infront of the control piston (pressure balance).The internal control system precisely controlsthe solenoid output power by flux modifica-tion.

As a result of this accurate control technolo-gy, the output pipe of the I/H converter is al-ways provided with the exactly requiredpressure for positioning the steam valve.

Example of Application

Modernisation of a 3-house Siemens extrac-tion/condensing turbine. Control stationTURCON®D-32, generator power limitation

VGB PowerTech 3/2005 3

Modern Control and Actuating Systems on Steam Turbines

Modernisation of Control and Actuating Systems on Steam Turbines

AutorenAutoren

R. Schilling

Voith Turbo GmbH & Co. KG,Electronic Drive Systems, Sales ManagerControl Systems, Crailsheim/Germany.

F. Hofmann

Voith Turbo GmbH & Co. KG,Electronic Drive Systems, Project Manager,Crailsheim/Germany.

Servomotor

Tank

Pump

Pro

cess

con

trol

eng

inee

ring

+ -

Setvalue

w

Magneticforce control

Pressurebalance

X0

PIU

X1

Pressure rangeadjustment

P

P

I/H converter - DSG

U

UB

BB

F

sValveposition

Steamcontrol valve

Live steam

Figure 1. Diagram I/H converter.

250 MW, start-up programme with detailedmonitoring of temperature difference ( F i g -u r e 2 ).

Conve r t e r Modu le s

Redundant design of I/H converter.

Application

Positioning of steam control valves in appli-cations with critical availability.

Design

Each I/H converter is provided with an elec-tronic monitoring system ensuring that theI/H converter reduces the pressure towardsminimum output pressure in the event of afailure. The output pressure of the properlyworking I/H converter is transferred. Theprocess continues smoothly. The defectivedevice can be replaced during operation.

Function

The two electric positioning signals (4 – 20 mA) of a redundant controller are in-dependently converted into a proportionalhydraulic pressure by one I/H converter each.

Both pressures act on a hydraulic maximumselection. The higher pressure is switched.With integrated test functions in turbine con-trol systems the hydraulic function is contin-uously monitored via additional pressure sen-sors by reducing the setpoint during normaloperation. These pressure variations avoid“sticking” of moving parts due to impurities.

Example of Application

Modernisation of an AEG-Kanis V40 extrac-tion steam turbine used for propulsion of acrude gas compressor. Turbine power ap-

proximately 18 MW, built in 1975. Redun-dant control station TURCON®R2 with com-puter, cable and input/output redundancy, in-corporation in the existing control systemthrough Modbus interface.

Way Va lve

Way valves convert an input signal 0/4 – 20 mA into proportional stroke onsingle- or double-acting hydraulic cylinders.The way valves (also referred to as flow con-troller) are electro hydraulic inverters withintegrated positioner and cascade magneticforce controller.

Application

Adjustment of positioning cylinders for thecontrol of turbo machinery.

Design

A “way valve” (flow controller) is an electri-cally controllable way valve consisting ofa power-controlled solenoid and a 3/3-wayhydraulic unit for single-acting cylinders or4/3-way hydraulic unit for double-actingcylinders ( F i g u r e 3 ).

FunctionDepending on the degree of deviation (set-point w – actual value x) and the set gainKPU, a command variable UMAG is createdfor the magnetic force controller. The mag-netic force FMAG generated in the magneticsystem is indirectly recorded by measuringthe magnetic flux UHall. FMAG affects the con-trol piston of way valve via tappet that ismoved against the control spring until theway-depending spring force FF is in balancewith force FMAG, resulting in a volume flowvariable in direction and size, which activatesan externally situated hydraulic cylinder.When the actual position is recorded andtransmitted to the positioner integrated in theway valve, the hydraulic cylinder is adjustedto a controlled position.

Example of Application

Modernisation of a 3-house AEG-Kanis dou-ble extraction turbine G32 17606+GE50K17607, generator power approximately 8 MW.Redundant control station Turcon®R2 withcomputer, cable and input/output redundan-cy, incorporation in the existing control sys-tem through Modbus interface.

Se rvomoto r s

Electro-hydraulic servomotor for the adjust-ment of valves or valve groups.

Application

Activation of control valves on turbo ma-chinery.

4 VGB PowerTech 3/2005

Modern Control and Actuating Systems on Steam Turbines

Figure 2. Application example I/H converter.

FM QSFKPU KPD

PI

TP

s

Us

X0X1

+P

+

-

+

+

+

IActualvalue

x

Setvalue

w

IU

U

Proc

ess

cont

rol e

ngin

eerin

g

Positioncontrol

Servomotor

Magneticforce control

Scaling

actualposition

Actualposition

Valveposition

Way valve

Positionpick up

Flow control way valve - WSR

UB

BFB

U

-UHall

UMAG

FMAG FF

Live steam Steamcontrol valve

Figure 3. Diagram flow control way valve.

Design

A servomotor is the intelligent and compactelectro-hydraulic combination of a controlsolenoid with integrated positioner, hydraulicflow controller and a hydraulic cylinder.

The supplier is able to completely check andadjust servomotors. The customer is providedwith an actuator with clearly defined inter-faces ( F i g u r e 4 ).

Function

A position setpoint selects a magnetic forcesetpoint. The magnetic force generated modi-fies the position of the control piston againstthe spring force and thus supplies the dosedpressurised oil to the hydraulic cylinder. Themagnetic force is returned to the magneticforce controller by measuring the magneticflux.

The force resulting from restoring springforce along with the external force and thehydraulic force moves the piston spindle sothat the actual position, measured by meansof a position sensor, follows the set position.

Examples of ApplicationPilot Valve Adjustment

Modernisation of a Borsig steam turbine usedfor propulsion of a boiler feed pump drive,turbine power approximately 2.4 MW. Theservomotor takes over angular positioningcontrol of the valve cam shaft. Control sta-tion Turcon®D, turbine protection 2 out of 3votes including electronic overspeed protec-tion system and axial shaft monitoring.

Valve Group Adjustment

Modernisation of a Creusot-Loire turbineused for propulsion of a compressor, built in1975, turbine power 13 MW. Conversion ofcontrol valve drive with complete servomo-tor. Redundant control station Turcon®R2with computer, cable and input/output redun-dancy ( F i g u r e 5 ).

Single Valve Adjustment

Modernisation of an AEG-condensation tur-bine used for propulsion of a boiler feedpump drive. Five live steam control valvesare positioned by five directly coupled servo-motors. Control station Turcon®D, turbineprotection 2 out of 3 votes including elec-tronic overspeed protection system and axialshaft monitoring.

Control Engineering

Depending on the existing or required degreeof automatisation, differing requirements areset upon the turbine control system. Moreand more efficient hardware, following thegeneral trend in computer technology, offersfree capacity for additional functions.

VGB PowerTech 3/2005 5

Modern Control and Actuating Systems on Steam Turbines

BF

UB

FM QSF

UB

KPU KPD

PI

TP

s

Us

X0X1

+P

+

-

+

+

-+

IActualvalue

x

Setvalue

wI

U

U

Proc

ess

cont

rol e

ngin

eerin

g

Positioncontroller

Power cylinderwith spring

magnetic force controller

Standardisationactual position

Actualposition

Live steam

Valveposition

Way valve

Steamcontrol valve

Servomotor

Positionpick up

Figure 4. Diagram servomotor.

Figure 5. Application example servomotor.

Standa rd Func t i ons

— Speed control:Automatic run-up, from starting automat-ic start-up to synchronous speed withtemperature-dependent ramps. Holdingpoints and rapid run-through resonanceareas can be configured.

— Load settings:Automatic start-up of the load ramp fromthe pre-selected initial load to the pre-se-lected final load after closing the genera-tor switch.

— Extraction pressure control:Smooth extraction pressure control sys-tems which can be connected and discon-nected, optional temperature control.

— Live steam and back pressure control:Pressure control systems which can beconnected and disconnected smoothlyand which can be automated using exter-nal input signals (e.g. generator switch,island operation).

— Limiting stages:Priority controlled limiting stage to mon-itor e.g. minimum live steam or maxi-mum output ( F i g u r e 6 ) .

Add i t i ona l Func t i ons

In addition to the original speed control andpressure control functions on a steam turbine,the turbine control systems take over a wholeseries of additional functions:

— integration of machine-related links,

— control of drives for pumps and valves,

— integration of limiting and monitoringdevices,

— data acquisition for condition-orientedmaintenance,

— control of feedwater quantity,

— condenser pressure limitation,

— rotary angle position control for valvecam shafts,

— additional logics to control a steam by-pass,

— integrated visualisation,

— test functions for overspeed protection orredundant actuation,

— surge limitation control, surge protectionand discharge pressure control for com-pressors ( F i g u r e 7 ).

Sys t em Fea tu r e s

Modular hardware and software allow con-figuring turbine control systems for simpleand complex applications in accordance withcustomer requirements.

Hardware:

— Usage of wide-spread computer plat-forms allows customer’s participation intechnical progress.

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Modern Control and Actuating Systems on Steam Turbines

Live steam HP-trip-valve HP-RV

LP-RV

I/H conv.

I/H conv.

Generator

w

x pL

1

w

<

Central limiting stage

>

Limitingoperation

Speedcontroller

Extractioncontroller

Back pressurecontroller

Live steamcontroller

Mixi

ng s

tage

HP LP

yn yHP

yEx yLP

xnxp

xpEx

y Exy n

wpEx

wpBack

wpLivew

1Steam pipeElectr. signal lineHydraulic pipe

xpBack

Figure 6. Standard functions turbine control system.

1

1Speedcontroller

wn

xn

Live steam

HP-trip-valve

HP-RV

Hydrogen

Process primar y control system

Suctionpressurecontroller

Suctionpressuresetpoint

HP

MAXDischargepressurecontroller

Pumplimitcontroller

Actualvalue q

Setpointqmin

pHP

xp suction

xT suction

xp dis

vy

y

w

x w

xp suction

wp

Steam pipeElectr. signal lineHydraulic lineGas line

I/H conv .

Figure 7. Additional functions turbine control system.

Webvisualisation

Diagnostic

Programming

LAN-Modem

Modem

Customer

Parametrisation Visualisation

Ethernet-LAN

TURCON® D-32

V oithCrailsheimGermany

Figure 8. Remote diagnostic turbine control system.

— Many logs and interfaces are availablefor data exchange with primary controlsystems.

— High availability is reached by use offlash memories, low-power-CPUs withpassive cooling and special power packswithout fan. Thus, the computer hardwareworks without moving/rotating parts.

Input/output modules:

— Usage of standard field bus systems al-lows flexibly configuring inputs/outputsand a great variety of modules.

— Decentralised signal acquisition allowsminimum cabling.

Software:

— Real-time multitasking operating systemsoffer fixed cycle times for processing ofcontrol programs.

— Efficient PLC operating systems alloweasy integration of customer-specificfunctions.

Redundant control systems are appropriatefor customers with high demands as to relia-bility. Features of redundant control systems:

— Computer redundancy, cable redundancy,input/output redundancy.

— Smooth change-over of all control andlimiting functions in the event of failurein the process managing system to theparallel operating system.

Se rv i ce F r i end l i ne s s

High operating convenience, user-orienteddata presentation and filing as well as errordiagnosis, if necessary, is expected from up-to-date turbine control systems:

— Minimum service cost due to remotemaintenance and optimisation via mo-dem.

— Programme alteration possible with run-ning machinery( F i g u r e 8 ).

Summary

High-capacity control and actuating compo-nents for the control of steam mass flows onsteam turbines offer advantages not only fornew equipment. Modernisation of the me-chanical hydraulic control solves problems inspare parts purchasing and improves the con-trol behaviour.

Depending on the condition of the former ac-tuating system, various modernisation alter-natives are available.

Apart from the original speed and pressurecontrol on steam turbines, advanced turbinecontrol systems are able to satisfy a numberofadditional functions.

In close co-operation with the operator themost sophisticated solution in regard to botheconomy and technology will be found. �

VGB PowerTech 3/2005 7

Modern Control and Actuating Systems on Steam Turbines

Voith Turbo GmbH & Co. KG

Electronic Drive Systems

P.O. Box 1555

74555 Crailsheim

Phone: +49 7951 32-0

Fax: +49 7951 32-605

turcon@voith.com

www.voithturbo.com

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