Process Engineering Equipment Handbook Episode 2 Part 1 pot

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 the
coupling.
A method for protection of gas turbines against overtorque and overspeed is
described 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 the
torque also must be able to cope with the misalignment and the displacement
caused 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 to
20,000 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 more
sensitive to the overloads that can appear when there is a malfunction in the
system.
Fault conditions. From a power transmission point of view the drive during normal
running 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 the
system, is a rare failure event.
If we discount mechanical failures, the main potential source for overtorque is

the 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 power
transmission components.
The electric fault possibilities are
᭿
Malsynchronization
᭿
Short circuit
Both events involve torque peaks at the generator output shaft of a magnitude ten
times full load torque (10¥ FLT). The peaks are of short duration and the torque is
pulsating with the frequency of the generated current. Malsynchronization only
gives few torque peaks while in a short circuit situation the pulsation of the torque
can go on for some seconds.
The nature and exact size of the torque peaks are well defined and normally
known 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 Allison
501-KB7 and GE’s LM 6000 need protection at approximately 2–2.5 ¥ FLT in certain
configurations.

Compared to most other drives protected with torque-limiting couplings the
relation between the requested torque limit and the FLT is unusually small. A
shearpin coupling is inadequate for such applications.
Basic design. The basic design principle of this OEM’s (Safeset
®
) coupling is to
transmit 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 the
frictional 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, and
consequently the transmitted torque drop to zero. The drop in torque occurs in a
few 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 practically
unchanged after a large number of load cycles. The coupling will thus not release
unneccesarily.
᭿
The torque limit is adjustable and can be set at low levels, i.e., 1.4–1.6¥ FLT and
thereby 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 loaded
steel mill drives and pump drives in the chemical industry, where production
downtime costs can be extremely high.
Overspeed and overspeed limits. When a gas turbine is mechanically disconnected
from 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 the
system, 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 the
residual energy. Therefore there is a significant influence based on where in the
drivetrain the mechanical disconnection takes place.
If the separation is made between the gearbox and the generator, the
overspeeding gas turbine will have to accelerate not only its own inertia but also
the 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 requires
certain 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 the
overspeed, and this can be done by including a hydrodynamic coupling in the
drivetrain.
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 the
generator.
The hydrodynamic principle. The torque transmission behavior of a hydrodynamic
coupling (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 w
p
, speed ratio (slip) n, acceleration
The torque transmission behavior of the turbo coupling can be described with the
following formula.
T =l· r · d
p
5
· w
p
2
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 the
profile design.
Typical l-slip curves for a typical OEM’s couplings with various fluid levels are
shown in Fig. C-370.
Two main features of the hydrodynamic coupling are the torsional separation and
damping.
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 dynamic
behavior of the complete system. This will result in lower stressing of component
parts and reduced stimulation.
Different applications require specific hydrodynamic coupling designs. For
example:
᭿

Constant fill coupling: soft start of electric motors, torque limitation on the driven
machine
᭿
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 various
requirements.
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 the
overspeed within acceptable limits, a slipping turbo coupling can be used between
the 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
᭿
High availability
Brake properties at high speed and acceleration. Figure C-372 shows the torque
transmission of a turbo coupling versus slip for generator speeds of 3000 and
3600 rpm.
FIG.
C-370 Typical slip curves for various filling levels. (Source: J.M. Voith GmbH.)
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 system
Figure 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 the
output shaft. A friction joint connects the input shaft to the sleeve 3.
The friction forces are generated by pressuring the hollow sleeve 4. The slipping
torque 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 rotate
relative to the output side. The relative movement (slip) is used to cut open the
head of valve 6 (shear tube). The oil pressure in the hollow sleeve is released and
the torque transmission is interrupted. The pump-wheel 7 of the turbo coupling is
connected to the flanged sleeve (input) and the turbine wheel 8 is connected to the
flanged-shaft (output). The acceleration of the gas turbine results in a speed
difference 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 and
removal 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 significantly
lower speed using a Safeset
®
and turbo coupling can clearly be seen. The calculation
assumes 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 consequences
for 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 with
power fluctuations.
The power behind thunderstorms can cause problems for industrial facilities
where 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 and
removal 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 significantly
lower speed using a Safeset
®
and turbo coupling can clearly be seen. The calculation
assumes 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 consequences
for 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 with
power fluctuations.
The power behind thunderstorms can cause problems for industrial facilities
where 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., and
the Electric Power Research Institute (EPRI) in Palo Alto, Calif., tried to eliminate
the problem by compensating voltage fluctuations with the PQ2000 energy storage
system designed by AC Battery Corp. in East Troy, Wis.
Oglethorpe Power selected the Brockway Standard Lithograph plant in
Homerville, Ga., as the site for the first commercial installation of the PQ2000
system. The Brockway facility is a prime location to test the power-compensation
system because southeast Georgia has one of the highest rates of lightning in the
United States; the flat terrain is also susceptible to high winds and hurricanes that
can cause power disturbances.
The Homerville plant houses four production lines, each equipped with high-
temperature drying ovens, that are used to cure printed metal for canned products
such as Folger’s Coffee cans in the United States as well as paint and brake-fluid
cans. 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 an

outage, occur. The outages also triggered the protective devices that turned off the
plant’s ovens. Plant workers had to purge the oven systems of gas before relighting
them, a 15-minute process for each line.
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 voltage
provided 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 the
utility system to protect the load from the disturbance. Once the utility system
returns 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 power
disruptions typically last only a few cycles, so the AC Battery engineers designed
the 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 various
utility disturbances ranging from a voltage sag to a complete outage up until
successful reclosure. Synchronization is maintained. The PQ2000 and other
improvements, such as properly grounded and improved electrical drives, trimmed
the Homerville factory’s annual electrical costs from a high of $110,000 to $120,000
down 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 semiconductor
manufacturing 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 a
hospital.
Other power supply improvements*
Harmonic distortion in distribution networks is a growing problem due to the
increased amount of low-pulse power electronic equipment going into service.
Power supplies for computers, UPS systems, and fluorescent lamps produce

harmonic 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.
C-352 Control Systems; Controls
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,
July 1998.)
Business areas with large concentrations of office blocks can generate power quality
problems.
Voltage sags are more common than complete outages. When major faults do
occur on the distribution system, the customer’s voltage can drop significantly (20
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 to
perform. 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 be
put down to reliability, not quality, problems. See Figs. C-378 and C-379.
All the major manufacturers offer solutions to poor power quality. These include
two technologies: FACTS (flexible AC transmission systems) and HVDC (high
voltage 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 power

transmission 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 AC
networks, 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 distance
and converted back to AC to supply a receiving AC network.
Using direct voltage and direct current, no reactive power is transmitted, line
losses 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 isolated
communities.
At the heart of the system is a voltage sourced converter, which is a DC
transformer of sorts, with the relationship between direct input voltage and the
output 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 the
source of many power quality problems arising from the operation of its electric arc
furnaces that affected surrounding users. Voltage flicker, harmonics, and current
unbalance 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 the
local network but improve the mill’s productivity, energy consumption, and power

factor. 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 Is
Changing” given by GEC Alsthom T&D Power Electronics Systems for the IEE
Power Division in London.)
Controls, Retrofit
Frequently, the retrofit of an entire control system is an efficent way to optimize
the performance of a plant. Many turbomachinery packages, including gas- and
steam-turbine–driven ones, are in good mechanical working order but need their
control 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 regulators
with a modern, reliable application control package that runs on an advanced PLC-
based system. The control package for the gas turbine provides fuel control, bleed
valve 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
large voltage variability tap changer SVC

voltage variability but location — relocatable SVC or
unpredictable Statcom
very long line shunt reactor series capacitor SVC or Statcom TCSC or SSC
stability limit reached series capacitor TCSC or SSC
subsynchronous resonance detune; reduce series capacitor TCSC or NGH damper
long distance instability higher voltage, new lines HVDC long distance
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
connect unsynchronized systems — HVDC long distance
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
sharing — unified power flow controller
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 simplifying
network installation.
᭿
Improved fuel regulation: Fast loop sampling rate, combined with modern digital

control techniques improve steady-state setpoint control and reduce overshoot
during transients.
᭿
Improved startup reliability: Special “lean lightoff ” procedure ignites all
combustors with essentially 100 percent reliability and with reduced thermal
stress.
᭿
Improved engine temperature monitoring and control: Advanced statistical
algorithms detect turbine hot/cold spots and automatically reject failed
thermocouples.
᭿
Fail-safe features: Redundant overspeeds, open/short monitoring of mA and
thermocouples, read-back monitoring of outputs, and special self-check features
improve safety.
᭿
Nonproprietary interfaces: Simple 4–20 mA, RTD, thermocouple, and dry contact
I/O allow simple interface of existing sequence/protection logic unit, making low-
cost partial upgrades practical and system troubleshooting easier.
᭿
Improved operator information with optional MMI: Optional Man-Machine
Interface (MMI), MS Windows-based graphic operator interface, displays system
status, trending, and data logging, which can be used as part of a preventative
maintenance program.
Scope of supply. The application control package for aeroderivative gas turbine
compressor 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.)
Controls, Retrofit C-357
᭿
Analog inputs, frequency:
᭿
Three redundant NGP
᭿
Three redundant NPT
᭿
Analog inputs, mV:
᭿
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
᭿
Operating states:
᭿
Firing

᭿
Warmup
᭿
Accelerate
᭿
Load
᭿
Status, alarms, and shutdowns:
᭿
Fault
᭿
GP (gas producer) overspeed alarm
᭿
GP underspeed shutdown
᭿
GP overspeed shutdown
᭿
Redundant GP overspeed shutdown
᭿
DGP alarm
᭿
NPT (power turbine) overspeed alarm
᭿
NPT underspeed shutdown
᭿
NPT overspeed shutdown
᭿
Redundant NPT overspeed shutdown
᭿
DNPT alarm

᭿
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
᭿
GP speed #1
᭿
GP speed #2
᭿
GP speed #3

᭿
GP speed #4
᭿
GP speed #5
᭿
NPT speed #1
᭿
NPT speed #2
᭿
TIT switch #1
᭿
Manual
᭿
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
᭿
Ramps:
᭿
Firing (lean lightoff) ramp
᭿
Startup ramp
᭿
Loading ramp
᭿
Cooldown ramp

᭿
Does not include:
᭿
PLC hardware
᭿
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 software
package

᭿
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 for
outdated electrohydraulic and analog-electronic controls. The PLC-based system
can include turbine and generator sequencing, complete turbine control, load
control, 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 systems
and components are also typically made available for complete or partial system
upgrades:
᭿
Fuel control valve system upgrade can include replacement of fuel control valve,
fuel speed ratio valve upgrade, addition of a fuel vent valve, compressor discharge
pressure 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 gas

turbine.
᭿
Complete second-stage nozzle actuator and hydraulic system retrofit for GE
Frame 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.
᭿
Thermocouple retrofits.
᭿
Skidded water or steam injection systems for NO
x
reduction.
Application case 3
Retrofit controls systems are available for fully integrated, multiloop,
microprocessor-based antisurge control and real-time performance monitoring
for multiple-stage (tandem) turbocompressors. See Figs. C-383 and C-384.
Additionally, the system can provide a variety of compressor control options (see
Figs. C-385 through C-397), which makes it a completely integrated compressor
control system.
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 each
compressor 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 superior
response to upsets and improved compression process stability.
᭿
Digital curve fit surge control lines for each stage produce constant safety
margins for safe operation and reduced recycle.
᭿
Adaptive control strategies continuously adjust control safety margins to actual
compressor stage operating conditions.
᭿
Loop-gain linearization allows equal percentage valve trim for improved
stability 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 sequence
functions 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 strategies
are 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 loading
sequences of multiple-stage compressors.
᭿
Failed transmitter fallback algorithms: Fallback algorithm allows continued, safe
operation in the event of a critical transmitter failure. Critical transmitters
include 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 during
changing 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 of
the compressor performance map and therefore is immune to inaccuracies in the
compressor’s respective map.
᭿
Increased analog input capability: Separate transmitter inputs for control and
performance monitoring allow flexibility for optimization of control while also
maximizing accuracy of performance calculations.
᭿
Assignable AUTO/MANUAL control block with flexible operator interface:
AUTO/MANUAL station allows the manual adjustment of up to eight controllers
from 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