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

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.

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:
᭿

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

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

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

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

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

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

᭿
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

᭿
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

᭿
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:

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

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,

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