Process Engineering Equipment Handbook Episode 2 Part 1 pot

Inertia of input side Inertia of output side Disconnection time of the generator Losses in the generator drag torque Torque/speed/time behavior of the gas turbine considering the acc

C-342 Control Systems; Controls

FIG C-365 Seal oil system for floating ring seals; API equivalent system (Source: Sulzer-Burckhardt.)

Control Systems; Controls C-343

FIG C-366 Lube oil unit (Source: Sulzer-Burckhardt.)

FIG C-367 Lube oil unit according to API 614 (Source: Sulzer-Burckhardt.)

possible because of potential overspeed of the turbine after the release of thecoupling

A method for protection of gas turbines against overtorque and overspeed isdescribed below The overspeed limitation is achieved through the incorporation of

a hydrodynamic coupling, acting as a brake

A gas turbine generator set normally consists of three major mechanical components, a gas turbine, a gearbox, and a generator

These components are connected with couplings that besides transmitting thetorque also must be able to cope with the misalignment and the displacementcaused by the temperature gradients in the system

The generators operate at standard speeds, 1500 (1800) rpm or 3000 (3600) rpm.The gas turbine speed differs with the individual turbine design from 3600 to20,000 rpm, typically

A gearbox that reduces speed is required in practically all generator set designs.The gear ratio can be as high as 12 times and different types of gearboxes are used

Aeroderivative gas turbines are based on aircraft engines with only minor design modifications The lightweight design however also makes the turbines moresensitive to the overloads that can appear when there is a malfunction in thesystem.

Fault conditions. From a power transmission point of view the drive during normalrunning conditions can be considered as smooth with small variations in the torque.The overtorque that can appear, and which has to be considered in designing thesystem, is a rare failure event

If we discount mechanical failures, the main potential source for overtorque isthe generator

Electrical fault conditions in the generator can produce a large overtorque that is transmitted back to the system: the turbine, the gearbox, and the powertransmission components

The electric fault possibilities are

 Malsynchronization

 Short circuit

Both events involve torque peaks at the generator output shaft of a magnitude tentimes full load torque (10¥ FLT) The peaks are of short duration and the torque ispulsating with the frequency of the generated current Malsynchronization onlygives few torque peaks while in a short circuit situation the pulsation of the torquecan go on for some seconds

The nature and exact size of the torque peaks are well defined and normallyknown by the generator manufacturer

How the torque peaks are transmitted backward through the system is governed

by the inertia and the stiffness of the components involved

The situation is complex and a dynamic analysis of the torque fault conditions

is normally required for determination of the torque that reaches the gas turbine

Torque-limiting requirements. The turbine itself, which also is the most costly item,

is in many cases the weakest link that has to be protected The requirement for

C-344 Control Systems; Controls

FIG C-368 Gas turbine generator set, general layout (Source: J.M Voith GmbH.)

Control Systems; Controls C-345

limiting the torque can in many cases be difficult As examples, both the Allison501-KB7 and GE’s LM 6000 need protection at approximately 2–2.5 ¥ FLT in certainconfigurations

Compared to most other drives protected with torque-limiting couplings therelation between the requested torque limit and the FLT is unusually small Ashearpin coupling is inadequate for such applications

Basic design. The basic design principle of this OEM’s (Safeset®) coupling is totransmit the torque through a frictional joint in which torque capacity is controlled

by hydraulic pressure This coupling type connects a gear to a shaft in Fig C-369

If the coupling is exposed to a higher torque than it can transmit over thefrictional joint it will slip there The relative movement of this slippage cuts a valve(shear tube) with a shear ring so the hydraulic pressure, the contact pressure, andconsequently the transmitted torque drop to zero The drop in torque occurs in afew milliseconds

This coupling has some basic advantages that has made it an appropriate solution

in certain gas turbine generator set applications

 The torque limit is not influenced by high fatigue and remains practicallyunchanged after a large number of load cycles The coupling will thus not releaseunneccesarily

 The torque limit is adjustable and can be set at low levels, i.e., 1.4–1.6¥ FLT andthereby protect components that have to operate close to their limits

 The resetting of the coupling after release is quick and reliable so the downtime

of the unit is minimized

Typical applications outside of the power generation field are very highly loadedsteel mill drives and pump drives in the chemical industry, where productiondowntime costs can be extremely high

Overspeed and overspeed limits. When a gas turbine is mechanically disconnectedfrom the workload and inertia of the generator it will momentarily increase speed.The magnitude of the speed increase is controlled by the residual energy in thesystem, i.e., the amount of fuel that is available and how it progresses to flame out.The overspeeding is also controlled by the inertia that is accelerated by theresidual energy Therefore there is a significant influence based on where in thedrivetrain the mechanical disconnection takes place

If the separation is made between the gearbox and the generator, theoverspeeding gas turbine will have to accelerate not only its own inertia but alsothe inertia of the gearbox, which will result in a lower peak speed

Speed is a critical design factor for a gas turbine and any overspeeding requirescertain actions depending on how much the speed is exceeded

Such actions could be:

 Inspection of the turbine

 Removal and complete disassembly

For the operation and for reducing the hazards it is important to reduce theoverspeed, and this can be done by including a hydrodynamic coupling in thedrivetrain

The requirements on the turbo coupling are limited by letting the coupling rotate

at speed and only react to the speed difference between gas turbine and generator

The braking torque is thus acting toward the relatively large inertia of thegenerator.

The hydrodynamic principle. The torque transmission behavior of a hydrodynamiccoupling (turbo coupling) is dependent mainly on the following factors

 Geometry: profile design, diameter d p

 Operating fluid: density r, fluid level, viscosity n

 Operating conditions: input speed wp, speed ratio (slip) n, accelerationThe torque transmission behavior of the turbo coupling can be described with thefollowing formula

T = l · r · d ·w

C-346 Control Systems; Controls

FIG C-369 Coupling basic design principle (Coupling is a Safeset™.) 1, shaft; 2, hub; 3, hollow steel sleeve; 4, antifriction bearings (on each side); 5, seal (on each side); 6, shear ring; 7, shear tube; 8, oil charport (Source: J.M Voith GmbH.)

Control Systems; Controls C-347

The performance coefficient, l, is dependent on fill level, speed ratio (slip), and theprofile design

Typical l-slip curves for a typical OEM’s couplings with various fluid levels areshown in Fig C-370

Two main features of the hydrodynamic coupling are the torsional separation anddamping

Input and output speeds or torque fluctuations are dampened or completely separated from input to output side, depending on the frequency

These features have a positive effect in all applications in respect to the dynamicbehavior of the complete system This will result in lower stressing of componentparts and reduced stimulation

Different applications require specific hydrodynamic coupling designs Forexample:

 Constant fill coupling: soft start of electric motors, torque limitation on the drivenmachine

 Variable speed coupling: control of driven machine speed

 Clutch-type coupling: separating driver and driven machine

Specific coupling and profile designs have been developed to meet the variousrequirements

The residual energy in a gas turbine after the release of this coupling will result

in acceleration to the turbine because of its relatively low inertia To keep theoverspeed within acceptable limits, a slipping turbo coupling can be used betweenthe gas turbine and the generator, which has a relatively high inertia (Fig C-371).For this application the turbo coupling must meet the following design criteria

 Rapid torque buildup with increasing slip

The development of the turbo coupling was conducted on a circuit that had good torque transmission capability at very high acceleration Tests on the circuit design were carried out up to a slip of 16 percent and a maximum acceleration of

6000 rpm

The features of the turbo coupling unit include:

 Resetting of the system after release

 Self-contained unit, easily removed from the drive systemFigure C-373 shows a compact design for this unit with incorporated turbo coupling.The flanged-sleeve 1 on the input side is connected via the intermediate sleeve 3

to the flanged shaft 2 on the output side The serration connects the sleeve 3 to theoutput shaft A friction joint connects the input shaft to the sleeve 3

The friction forces are generated by pressuring the hollow sleeve 4 The slippingtorque can be set by varying the oil pressure in the hollow sleeve

C-348 Control Systems; Controls

FIG C-371 Gas turbine drive with Safeset ® and coupling (without gearbox) (Source: J.M Voith GmbH.)

FIG C-372 Torque transmission of a turbo coupling (Voith VTK) versus slip (Source: J.M Voith GmbH.)

Control Systems; Controls C-349

After reaching the maximum transmittable torque the input side will rotaterelative to the output side The relative movement (slip) is used to cut open thehead of valve 6 (shear tube) The oil pressure in the hollow sleeve is released andthe torque transmission is interrupted The pump-wheel 7 of the turbo coupling isconnected to the flanged sleeve (input) and the turbine wheel 8 is connected to theflanged-shaft (output) The acceleration of the gas turbine results in a speeddifference between the coupling wheels that generates a torque as shown in Fig C-

372 The torque is almost proportional to the slip (See Fig C-374.)

FIG C-373 Design of safety device consisting of Safeset ® coupling and turbo coupling (Source: J.M Voith GmbH.)

FIG C-374 Safety device after overload occurred (Source: J.M Voith GmbH.)

This OEM’s (Safeset®

) turbo coupling unit is designed in such a way that it can

be mounted between two membrane couplings This allows the assembly andremoval of the unit without disturbing the gearbox or the gas turbine

Simulations of LM 6000 fault events. Figure C-375 shows the speed response of a LM

6000 gas turbine and generator using the torque speed characteristic (Fig C-372)

of a turbo coupling (Voith turbo size 682)

The speed response without a turbo coupling is also shown The significantlylower speed using a Safeset®

and turbo coupling can clearly be seen The calculationassumes the following data are known

 Inertia of input side

 Inertia of output side

 Disconnection time of the generator

 Losses in the generator (drag torque)

 Torque/speed/time behavior of the gas turbine considering the acceleration

Controls, of Power Supply

Fluctuations and disturbances in a power supply can have expensive consequencesfor the process engineer A 2-s power interruption in a semiconductor plant cost over

$70,000 in 1997 dollars The following* cases illustrate the costs associated withpower fluctuations

The power behind thunderstorms can cause problems for industrial facilitieswhere electronic systems that control critical equipment are sensitive to the storms’slight voltage disturbances These brief voltage sags can disrupt process electronics,resulting in losses in production and costly downtime to recalibrate and restart the

C-350 Control Systems; Controls

FIG C-375 Speed response of the gas turbine and the generator with and without safety device (Source: J.M Voith GmbH.)

* Source: Adapted from extracts from “Compensating for Lightning,” Mechanical Engineering Power,

ASME, November 1997.

This OEM’s (Safeset®

) turbo coupling unit is designed in such a way that it can

be mounted between two membrane couplings This allows the assembly andremoval of the unit without disturbing the gearbox or the gas turbine

Simulations of LM 6000 fault events. Figure C-375 shows the speed response of a LM

6000 gas turbine and generator using the torque speed characteristic (Fig C-372)

of a turbo coupling (Voith turbo size 682)

The speed response without a turbo coupling is also shown The significantlylower speed using a Safeset®

and turbo coupling can clearly be seen The calculationassumes the following data are known

 Inertia of input side

 Inertia of output side

 Disconnection time of the generator

 Losses in the generator (drag torque)

 Torque/speed/time behavior of the gas turbine considering the acceleration

Controls, of Power Supply

Fluctuations and disturbances in a power supply can have expensive consequencesfor the process engineer A 2-s power interruption in a semiconductor plant cost over

$70,000 in 1997 dollars The following* cases illustrate the costs associated withpower fluctuations

The power behind thunderstorms can cause problems for industrial facilitieswhere electronic systems that control critical equipment are sensitive to the storms’slight voltage disturbances These brief voltage sags can disrupt process electronics,resulting in losses in production and costly downtime to recalibrate and restart the

C-350 Control Systems; Controls

FIG C-375 Speed response of the gas turbine and the generator with and without safety device (Source: J.M Voith GmbH.)

* Source: Adapted from extracts from “Compensating for Lightning,” Mechanical Engineering Power,

ASME, November 1997.

Control Systems; Controls C-351

equipment A pilot project funded by Oglethorpe Power Corp in Tucker, Ga., andthe Electric Power Research Institute (EPRI) in Palo Alto, Calif., tried to eliminatethe problem by compensating voltage fluctuations with the PQ2000 energy storagesystem designed by AC Battery Corp in East Troy, Wis

Oglethorpe Power selected the Brockway Standard Lithograph plant inHomerville, Ga., as the site for the first commercial installation of the PQ2000system The Brockway facility is a prime location to test the power-compensationsystem because southeast Georgia has one of the highest rates of lightning in theUnited States; the flat terrain is also susceptible to high winds and hurricanes thatcan cause power disturbances

The Homerville plant houses four production lines, each equipped with temperature drying ovens, that are used to cure printed metal for canned productssuch as Folger’s Coffee cans in the United States as well as paint and brake-fluidcans Fifteen adjustable-speed drives on the four lines control the printing process.Outages number 30 to 50 times per year due to storms at the Homerville facility.Three motor burnouts per month, due to poor-quality electrical service after anoutage, occur The outages also triggered the protective devices that turned off theplant’s ovens Plant workers had to purge the oven systems of gas before relightingthem, a 15-minute process for each line

high-Power disturbances caused both a safety concern and a productivity issue,because workers had to climb a 20-foot ladder to purge the burners

The PQ2000 system is designed to continuously monitor the utility voltageprovided to a commercial or industrial facility Whenever a disturbance is detected,the system switches and picks up the load, isolating itself and the load from theutility system to protect the load from the disturbance Once the utility systemreturns to normal, the PQ2000 system switches the load back to the utility

Speed is of the essence The PQ2000 can deliver up to 2 MW in about one-quarter

of a cycle (or 1/240 s) to maintain power to critical equipment Most powerdisruptions typically last only a few cycles, so the AC Battery engineers designedthe power-storage system to dispense power for up to 10 s, ensuring an extra margin

of safety

This system demonstrated its ability to protect plant operations from variousutility disturbances ranging from a voltage sag to a complete outage up untilsuccessful reclosure Synchronization is maintained The PQ2000 and otherimprovements, such as properly grounded and improved electrical drives, trimmedthe Homerville factory’s annual electrical costs from a high of $110,000 to $120,000down to $60,000 to $70,000 (see Figs C-376 and C-377)

Using this system to correct a 2-s power outage can save a semiconductormanufacturing plant $70,000 in product that would otherwise be lost The same 2-s interval can cause $600,000 in data processing losses for a computer center,require weeks of cleanup in a glass plant, or corrupt critical patient data at ahospital

Other power supply improvements*

Harmonic distortion in distribution networks is a growing problem due to theincreased amount of low-pulse power electronic equipment going into service.Power supplies for computers, UPS systems, and fluorescent lamps produceharmonic current which contributes significantly to the harmonics in the network

In low-voltage networks, mainly the third and the fifth harmonics are affected

* Source: This section is adapted from extracts from “Industry Needs Quality Supplies,” International

Power Generation, July 1998.

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FIG C-376 The PQ2000 system offsets voltage disturbances caused by storms, thereby preventing

costly production-equipment shutdowns (Source: Mechanical Engineering Power, ASME,

November 1997.)

FIG.C-377 Schematic for the wearing of the PQ2000 (Source: Mechanical Engineering Power, ASME, November 1997.)

Control Systems; Controls C-353

FIG.C-378 Network problems caused by the consumer (Source: International Power Generation,

to 30 percent) below its nominal value on one or more phases The embedded chips

in many production processes sense disturbances in this range and can fail toperform Both sags and complete interruptions can last from 100 ms up to a number

of seconds or until the fault is cleared by the auto-recloser Longer breaks can beput down to reliability, not quality, problems See Figs C-378 and C-379

All the major manufacturers offer solutions to poor power quality These includetwo technologies: FACTS (flexible AC transmission systems) and HVDC (highvoltage direct current) Both use power electronics and are set to develop quickly.The use of power electronics makes it possible to design equipment that allows fast and flexible control of power flows through AC transmission systems, giving continuous control of active/reactive power and increasing network capacity,stability, and quality HVDC is a proven technique employed by most electric powertransmission organizations for a variety of reasons

FIG.C-379 Network problems affecting the consumer (Source: International Power Generation,

July 1998.)

C-354 Controls, Retrofit

It is used on systems with long transmission lines for coupling dissimilar ACnetworks, and for submarine cables There are now distinct possibilities for using

DC converters to improve network power quality

HVDC equipment takes a supply from one point in an AC network and converts

it to DC in a converter station (rectifier) It is transmitted over a line of any distanceand converted back to AC to supply a receiving AC network

Using direct voltage and direct current, no reactive power is transmitted, linelosses are low, and power quality is high The OEM recently demonstrated a

DC application with the installation of a 10-kV, 3-MW compensator designed for specialist supply situations such as infeeds to cities and supplies to small isolatedcommunities

At the heart of the system is a voltage sourced converter, which is a DCtransformer of sorts, with the relationship between direct input voltage and theoutput voltage dependent on the relative conduction times of the valve connected

to the positive DC terminal and the valve connected to the negative DC terminal.Using pulse width modulation, most output voltage waveforms can be synthesized Specifically, a sinusoidal voltage can be generated, which means that unlike a conventional HVDC converter, a voltage source converter can supply

a passive AC load from a DC source Such a device (HVDC Light) was installed at

a Swedish steel mill to improve the network’s power quality The steel mill was thesource of many power quality problems arising from the operation of its electric arcfurnaces that affected surrounding users Voltage flicker, harmonics, and currentunbalance are a long standing complaint of neighbors of steel mills

The converter stations, rated at 3 MW at ±10.5 kVdc are connected on a 10 km

AC transmission line The installation will not only reduce quality problems on thelocal network but improve the mill’s productivity, energy consumption, and powerfactor This pilot installation will provide the technology for larger applications(initially up to 50 MW)

(Note: Table C-30 is taken from a paper “Power Transmission and How It IsChanging” given by GEC Alsthom T&D Power Electronics Systems for the IEEPower Division in London.)

Controls, Retrofit

Frequently, the retrofit of an entire control system is an efficent way to optimizethe performance of a plant Many turbomachinery packages, including gas- andsteam-turbine–driven ones, are in good mechanical working order but need theircontrol systems tweaked to maximize their potential It may be more cost effective

to retrofit the entire control system Some examples follow.*

Application case 1

The aeroderivative gas turbine application control package (see Fig C-380) replaces

older mechanical/hydraulic/electronic/pneumatic aeroderivative fuel regulatorswith a modern, reliable application control package that runs on an advanced PLC-based system The control package for the gas turbine provides fuel control, bleedvalve control, and inlet guide vane control

Advantages

 Hardware independent system: Application control package’s portability allows

choice of platform, reducing need for additional spare parts and training expenses

* Source: Petrotech Inc., USA.

Controls, Retrofit C-355

TABLE C-30 Comparison of Conventional Equipment and Power Electronic Solutions to Network Problems

Problem Conventional Solution Power Electronic Solution

low voltage at heavy load capacitor power factor correction —

high voltage at low load breaker switched capacitor/reactor —

low voltage on line outage breaker switched capacitor SVC

voltage variability but location — relocatable SVC or

interarea swings stabilizing signal in generator excitation —

unstable interconnection series capacitor, excitation damping HVDC back-to-back link persistent loop flow open connections, series reactors HVDC back-to-back link

poor parallel line sharing series capacitor/reactor or quad booster —

poor post-fault sharing breaker switched series —

continuous need to adjust sharing capacitor or quad booster TCSC or SSC

voltage variable and continuous poor — thyristor phase shifter

fault level limits series reactors HDVC back-to-back link more power needed, but new line cable, gas duct convert AC line to DC impossible

Key: SVC, static VAR compensator; Statcom, GTO thyristor-based SVC; TCSC, thyristor-controlled series capacitor; SSC, static series

compensator; NGH, subsynchronous damping circuit.

 Fault tolerant: Control package is available on ICS Triplex fault-tolerant

controllers for critical control applications Software functionality is extended to

2 out of 3 (2oo3) voting at the CPU and I/O level

 Simplified interface to DCS or SCADA: Communication tasks are handled with

a separate, dedicated module in the PLC, increasing data rate and simplifyingnetwork installation

 Improved fuel regulation: Fast loop sampling rate, combined with modern digital

control techniques improve steady-state setpoint control and reduce overshootduring transients

 Improved startup reliability: Special “lean lightoff ” procedure ignites all

combustors with essentially 100 percent reliability and with reduced thermalstress

 Improved engine temperature monitoring and control: Advanced statistical

algorithms detect turbine hot/cold spots and automatically reject failedthermocouples

 Fail-safe features: Redundant overspeeds, open/short monitoring of mA and

thermocouples, read-back monitoring of outputs, and special self-check featuresimprove safety

 Nonproprietary interfaces: Simple 4–20 mA, RTD, thermocouple, and dry contact

I/O allow simple interface of existing sequence/protection logic unit, making cost partial upgrades practical and system troubleshooting easier

low- Improved operator information with optional MMI: Optional Man-Machine

Interface (MMI), MS Windows-based graphic operator interface, displays systemstatus, trending, and data logging, which can be used as part of a preventativemaintenance program

Scope of supply. The application control package for aeroderivative gas turbinecompressor drive system includes:

 Analog inputs, 4–20 mA:

 Load setpoint (capacity control)

 Compressor discharge pressure (CDP)

 Ambient temperature (CIT)

C-356 Controls, Retrofit

FIG C-380 Simplified schematic showing an aeroderivative gas turbine compressor drive application control package integrated into an advanced PLC-based control system (Source: Petrotech Inc.)

 TIT (up to 18 thermocouples)

 Analog outputs, 4–20 mA:

 Fuel control valve position setpoint

 Inlet guide vane position setpoint (if applicable)

 Bleed valve position setpoint

 High TIT alarm

 High TIT shutdown

 Low TIT shutdown

 Low TIT delayed alarm

 Rejected thermocouple

 Shutdown in the event of too few thermocouples

 DT alarm

 DT shutdown

 Thermocouple spread alarm

 Thermocouple spread shutdown

 Turbine maximum limit

 Turbine minimum limit

 High firing fuel pressure shutdown

 Transmitter failure alarms

 Transmitter failure shutdowns

 Output failure shutdowns

 Control mode

 Controllers/special features:

 Start-up controller for fuel valve

 NGP (gas producer speed) controller for fuel valve

 NPT (power turbine speed) controller for fuel valve

 TIT controller for fuel valve

 TIT rate of rise controller

 Fuel acceleration schedule

 Fuel deceleration schedule

 Deceleration rate limiter

 Corrected speed (CNGP) override

 Inlet guide vane controller

 Bleed valve controller

 Combustion monitoring system

 Stagnation detection system

 Compressor application control package

 Gas turbine sequencing and protection discrete logic

 Compressor sequencing and protection discrete logic

 End elements

Options for complete control system upgrade

 Compressor application control package

 Gas turbine sequencing and protection discrete logic

 Compressor sequencing and protection discrete logic

 Communication interface to DCS or SCADA

 Capacity control application control package

 PLC hardware

 Man-machine interface unit with WonderWare InTouch® licensed softwarepackage

 Complete custom-engineered control panel, factory tested and ready to install

 Fuel control valve system upgrade

 Acceleration control valve system upgrade

 Inlet guide vane actuator system upgrade or retrofit

 Bleed valve actuator system upgrade

 Thermocouple upgrade

 Vibration system upgrade

 Installation and commissioning

 Training

C-358 Controls, Retrofit

Controls, Retrofit C-359

Application case 2

The Series 9500 integrated control system provides cost-effective complete or

partial control system retrofits for gas turbine–driven generator packages (see Figs.

C-381 and C-382) The Series 9500 system provides replacement controls foroutdated electrohydraulic and analog-electronic controls The PLC-based systemcan include turbine and generator sequencing, complete turbine control, loadcontrol, DCS interface, and a graphical operator interface for system status,trending, and data logging

Main features are similar to those for the system in the preceding case

The gas turbine generator control package includes:

 Firing (soft lightoff ) ramp

 Startup controller

 NHP controller

 NHP acceleration controller

 EGT controller

 EGT rate of rise controller

 EGT controller for inlet guide vanes (if applicable)

 Combustion monitoring system

 Dual fuel capability with online transfer

Auxiliary systems for gas turbine generator packages. The following auxiliary systemsand components are also typically made available for complete or partial systemupgrades:

 Fuel control valve system upgrade can include replacement of fuel control valve,fuel speed ratio valve upgrade, addition of a fuel vent valve, compressor dischargepressure transmitter, and interstage fuel pressure transmitter

 Dual fuel conversions including addition of a gas or liquid fuel valve system

 Hydraulic servocontrols if applicable, such as second-stage nozzle controls on

a GE Frame 3 gas turbine, or inlet guide vane controls on a GE Frame 5 gasturbine

 Complete second-stage nozzle actuator and hydraulic system retrofit for GEFrame 3, with an increased capacity industrial RAM and servo with accumulator,pumps, and support components integrated into a complete system

 Speed probe and exciter gear assemblies

 Flame detectors for combustion chambers

C-360 Controls, Retrofit

FIG C-381 Simplified schematic showing a advanced PLC-based integrated control system for a gas turbine generator set The system provides turbine fuel control, temperature control, sequencing/protection, and communication interfaces (Source: Petrotech Inc.)

Controls, Retrofit C-361

Retrofit system features include

 Multiple-stage compressor control capability: Provides integrated compressor

control for up to four compressor bodies in a single hardware platform Eliminates multiple-box control approach and simplifies controller-to-controller communication while also reducing overall system complexity and cost

 Built-in, proven algorithms for every application: Seven built-in algorithms for

each independent stage and ability to add customer-defined algorithms for eachcompressor stage

 Advanced control strategies enhance process stability:

 Each compressor stage controller is independently optimized

 Coordinated control action between stage controllers for runup, rundown,loading, and upsets is much smoother and faster than multiple-box systems

 Anticipation-based control and asymmetrically damped control provide superiorresponse to upsets and improved compression process stability

 Digital curve fit surge control lines for each stage produce constant safetymargins for safe operation and reduced recycle

 Adaptive control strategies continuously adjust control safety margins to actualcompressor stage operating conditions

 Loop-gain linearization allows equal percentage valve trim for improvedstability at lower recycle without requiring detuning for high recycle

 Valve actuator preload control eliminates delay in surge valve response.Typically, ASC-M3 systems have the valve full open on upsets in 3/4 s or less

 PURGE/RUNUP/RUNDOWN coordination feature provides optimum sequencefunctions without field solenoids, timers, or additional field cables

 Compressor efficiency increase: Energy consumption of driver is reduced by

eliminating unnecessary recycle

FIG C-382 Replacement controls for two GE Frame 5 generator sets in utility power generation peaking service (Source: Petrotech Inc.)

 Integrated compressor control options: Capability exists for integrated options

such as capacity control and pressure override control Advanced control strategiesare easily accomplished at a much lower cost than typical multibox systems

 Command initiatives on a per-stage basis: Individual PURGE and ON-LINE

contacts for each compressor stage allow for more complex, efficient loadingsequences of multiple-stage compressors

 Failed transmitter fallback algorithms: Fallback algorithm allows continued, safe

operation in the event of a critical transmitter failure Critical transmittersinclude compressor flow, suction pressure, and discharge pressure

 Molecular weight correction: Automatic surge line compensation for shifts

attributable to changes in molecular weight protect against surge duringchanging inlet gas conditions

C-362 Controls, Retrofit

FIG C-383 Simplified instrument diagram showing one ASC-M3 compressor controller in a four-stage compressor

application with a recycle valve for each stage Controls for each body are independently calibrated and configured per the requirements for the respective stage A single ASC-M3 can handle compressor control applications ranging from a single- stage compressor up to four independent stages, including various integrated control options and enhancements This flexibility eliminates a multiple-box approach and reduces overall system complexity and cost Each compressor body can have a different control algorithm, and can have flow measurement in the suction or discharge Runup, rundown, purge, loading, and upset control are coordinated between stages Built-in high-select and low-select functions can combine two, three, or four “controller” outputs to a single recycle valve if required Each ASC-M3 complete-train compressor controller

is individually factory configured with exactly the inputs, outputs, and control functions appropriate for the particular compressor Each controller requires an Application Engineering Service package, catalog item AES, which provides preliminary calibration and configuration, as well as bench test As shipped, as configured model ASC-M3 compressor controller typically requires only verification of the field wiring and minor field tuning to be placed in service (Source: Petrotech Inc.)

Controls, Retrofit C-363

FIG C-384 Simplified function block diagram showing the ASC-M3 control features for a single compression body Discrete outputs and the printer port are common for all stages (Source: Petrotech Inc.)

 Incipient surge detector: Detects mild surge and takes corrective action before a

violent surge occurs The incipient surge detection algorithm is independent ofthe compressor performance map and therefore is immune to inaccuracies in thecompressor’s respective map

 Increased analog input capability: Separate transmitter inputs for control and

performance monitoring allow flexibility for optimization of control while alsomaximizing accuracy of performance calculations

 Assignable AUTO/MANUAL control block with flexible operator interface:

AUTO/MANUAL station allows the manual adjustment of up to eight controllersfrom a single location

 Fault-tolerant capability: Hot backup configuration is available for critical control

applications via a transfer gate The transfer gate monitors the health of the main

C-364 Controls, Retrofit

Compressor performance curves showing a 10 percent safety margin established at design ratio, and 10 percent safety margin at the highest ratio ( FIG C-385) Calibration of 10 percent at design ratio results in a loss of safety as ratio increases Calibration of 10 percent at the highest ratio results in excess recycle and loss of efficiency This information source’s method ( FIG C-386) of digital curve fit results in a uniform safety margin across the entire operating range with no loss of efficiency due to excess recycle (Source: Petrotech Inc.)

386 385