POWER November 2012 - 20

augment or replace an existing instrument
system. EPRI estimates the cost of the
minimum system in the range of $120,000
to $180,000, the basic automatic system
at $150,000 to $270,000, and the complete
system at $225,000 to $300,000,
although specific site locations could add
additional cost.
A seismic instrumentation installation or
upgrade at a nuclear power plant is subject
to certain licensing considerations. It
should be noted first that voluntary implementation
of the earthquake-response
guidelines provided in the four EPRI references
listed in the sidebar, including installing
new seismic instrumentation, does
not generally require prior NRC approval.
This is a synopsis of an EPRI white paper
originally published in January 2012 and
available at no charge from www.epri.com.
Search for document 1024889.
-Edited by Dr. Robert Peltier, PE
Maximizing Steam Turbine/
Compressor Performance
with Precise Torque Monitoring
at the Coupling
All turbo machinery is subject to degradation
that, over time, will affect the system's
efficiency and operational performance.
Precise monitoring of turbo machinery performance
with continuous torque-monitoring
systems can be used to identify gradual
efficiency loss. That, in turn, allows a more
focused maintenance scope to be developed
that can return the system to its optimum
operation and efficiency.
Torque monitoring based on heat balance,
energy balance, and other methods
requires measuring numerous parameters
such as pressure, temperature, flow rate,
and gas composition, which require highaccuracy
instrumentation. However, phase
displacement technology can be used to
accurately measure torque directly at the
coupling to within 1% of full-scale torque,
a combination of all electrical and mechanical
sources of error.
Measure the Torque
A torque-monitoring system was recently
installed on a cracked-gas compressor
train at Qenos Olefins in Australia to determine
the causes of a power limitation.
The Kop-Flex Powerlign system installed
utilizes phase displacement technology
for long-term reliability, eliminating the
need for recalibration.
Two rings with pickup teeth are installed
on a torsionally soft spacer and
are intermeshed at a central location. Two
monopole sensors 180 degrees apart are
mounted on the coupling guard. As the
20
2. Tracking two signals. The Powerlign system produces two independent torque signals.
Source: Kop-Flex
Sensor 1
4
3
2
1
o
-1
-2
-3
-4
Time
3. Important stats. Typical output from Powerlign system includes torque, power, speed,
and temperature. Source: Kop-Flex
Torque
60,000
50,000
40,000
30,000
20,000
10,000
Power
Speed
Temp
60
50
40
30
20
10
Sensor 2
Time
coupling rotates, the ferromagnetic teeth
create an AC voltage waveform in the sensor
coil, which is digitally processed using
known calibration parameters. Because of
the intermeshed pickup teeth, the system
is referred to as a single-channel phase
displacement system, producing two independent
torque measurements (Figure 2).
The Powerlign system will output torque,
power, speed, and temperature, which can
be easily integrated with any distributed
control system (Figure 3).
At the Olefins plant the operating cycle
of the steam-driven, cracked-gas compressor
train is seven to eight years. During
this cycle the plant eventually has production
limitations because the compressor
train encounters a power limit. " Turbine
fouling " or " compressor fouling " or a combination
of both caused the power limit.
The true cause had long been the subject
of an engineering debate among the Machinery
group, Process Engineering group,
and Operations department.
www.powermag.com
The power loss was so important that
the plant considered upgrading the turbine's
power rating from 7.5 MW to 9 MW.
This upgrade would have required a capital
investment of $2 million, so the plant
elected to defer this investment and instead
installed a torque meter during the
last eight-year major overhaul shutdown.
The installation involved replacing
the existing coupling spacer and flexible
halves with a " drop-in " torque meter
and integral flexible elements (Figure 4).
The torque meter assembly was dynamically
balanced to API standards so it was
not necessary for the user to return any
coupling components for the retrofit. The
coupling guard was modified so that the
two variable-reluctance sensors could be
installed, completing the mechanical installation
(Figures 5 and 6).
Successful Restart
The plant was restarted after completing a
number of compressor efficiency improvePOWER
| November 2012
Value (N-m, kW, RPM)
Voltage
16:37:11
16:40:42
16:44:12
16:47:44
16:51:12
16:54:43
16:58:13
17:01:44
Temperature (C)
http://www.epri.com http://www.powermag.com
POWER November 2012

Table of Contents for the Digital Edition of POWER November 2012
