Types of Monitoring Systems:
There are two types of monitoring systems achievable with CMCP500 Series Transmitters and Monitors. The system can be specified as a stand-alone system with local displays and
alert/danger relays using CMCP500
Series Monitors. Alternatively the system can provide an output to a DCS/PLC,
(existing or a supplied Wonderware
HMI package), with just the use of CMCP500 Series Transmitters and Analog to Digital Converters.
CMCP can provide Analog to Digital converters to communicate in Modbus,
Ethernet or any other protocol.
Monitoring Parameters:
Radial Vibration is usually the heart of the TSI system. It gets the
most attention and generally gives the first indication of out of
specification conditions. Most OEM TSI systems utilized a shaft rider
transducer system to monitor vibration with a shaft absolute output
signal. An exact replacement transducer system can be supplied, but most
customers and OEMs are specifying Eddy Probe Systems. A complete vibration
system would install two probes per bearing, with the
sensors located 90° from each other (X and Y).
Thrust Position indication includes one or two Eddy Probe Systems to
observe the position of the thrust collar within its bearings. This system
is an internal installation and need not replace the existing system
because many original installations utilize a differential pressure system
that interfaces with the turbine hydraulic control system.
Shell Expansion is the measure of a turbine case or shell moves in
relation to a fixed location usually measured with a Linear Variable Differential
Transformer (LVDT). Some existing OEM systems still use spindle
micrometers or dial indicators that are subject to mechanical damage and
human error. Although many systems installed with only one LVDT are
adequate, a complete TSI system specification should consider two LVDTs
located at each corner of the turbine shell. A second sensor will monitor
shell cocking or uneven thermal growth which is a fairly common occurrence
during startup when the sliding feet may have inadequate lubrication.
Differential Expansion - measurements are an important parameter
receiving much attention during turbine startup and warming. This
parameter measures how the turbine rotor expands in relation to the
turbine shell, or casing. A new differential expansion system using Eddy
Probes can be retro-fitted to any existing system. An Eddy Probe is more
reliable and robust than OEM supplied induction coil systems.
Valve Position - Correct valve positioning is required to efficiently
operate a steam turbine. Some turbines may require several throttle valves
be monitored, and some turbines will instrument the main stop valve(s) to
determine when they crack from their seats.
Retro-fit valve position measurements use DC LVDTs. All OEM TSI systems include valve position measurement(s)
as a startup and operation parameter. Some OEM systems utilized AC LVDTs
while others use mechanical linkages and scales for indication. A
retro-fitted system can be installed in the same position or relocated
to a more accessible or protected position.
Eccentricity - A rotor which has been sitting idle during overhaul or
has been inadvertently stopped during coast-down for an extended period
will develop a bow or bend. This condition must be corrected by turning
gear operation and, possibly, with auxiliary heating prior to high speed
operation to prevent internal clearance rubbing.
Eccentricity systems installed by OEMs monitor the turbine stub shaft or a
shaft collar using induction coils. A retro-fit Eddy Probe system will
monitor at the same location, and many times use the same bracketry.
Speed - Turbine speed indication supplied by OEMs comes in many forms:
observing a gear wheel located inside the front standard, electrically
converting the generator output frequency, or monitoring the turning gear.
A retro-fitted system using Eddy Probe's can be specified to observe any
multi-toothed gear wheel. Applications monitoring generator output
frequency without an integral turning gear may require installation of a
custom gear wheel.
Speed indication may be specified as an analog display or as a digital
display and can be interfaced to a zero speed system for turning gear
engagement.
Rate of Acceleration is usually monitored during startup to prevent
over-torquing the rotors as the turbine approaches critical speeds, and
as the operating speed is reached prior to line synchronization. Once the
generator has been synchronized and is being controlled by load
dispatchers the acceleration rate is not monitored.
Acceleration rate measurements use a speed input to derive its output
display. Eddy Probe systems can be installed as a replacement or
supplement an existing application.
Phase or phase angle, is a measure of the relationship of how one
vibration signal relates to another vibration signal and is commonly used
to calculate the placement of a balance weight. This parameter is not
usually displayed continuously but is monitored periodically to determine
changes in the rotor balance condition, deviations in system stiffness
such as a cracked shaft.
Phase angle measurements are sometimes not supplied by OEMs, but can be
installed using an Eddy Probe system. Installation involves locating or
installing a once-per-turn event such as a key or notch that the Eddy
Probe will view. An Eddy Probe viewing a notch is easier to install and
adjust, but the installation of the notch requires special tooling to cut
the notch. Keys are easier to apply using glues or epoxies and are subject
to coming off due to centrifugal forces.
Temperature of bearings is a measure of the how hot a bearing is
operating. It may be due to overloading, mis-alignment, improper
lubricant pressure and/or flow.
Nearly all turbine generator bearings were originally installed or
retro-fitted with bearing temperature sensors. These sensors may be
thermocouples or RTDs. This parameter is often overlooked possibly due to
the OEM output display located at some other panel not within the vicinity
of the retro-fitted TSI system. Any bearings that was not originally
equipped with temperature sensors can be retro-fitted to accept
thermocouples or RTDs.
Single Channel Transmitters/Monitors:
Each
of the above channels is monitored with an individual CMCP500 Series
Transmitter or Monitor.
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Variations of CMCP540(A) and CMCP545(A) transmitters/monitors are used to
monitor turbine specific parameters including:
Turbine speed is monitored with the CMCPTACH3 Programmable Tachometer. The CMCP-TACH3 also displays Rate of
Acceleration.
Integration:
STI Vibration Monitoring Inc.
integrates the single channel CMCP500 Series Transmitters/Monitors into a
complete and reliable Turbine Supervisory Instrumentation package. Several enclosure options are available
ranging from NEMA4X fiberglass to cast aluminum explosion proof, all
available with or without windows. Local
displays are a popular option for transmitter systems and a must for the
stand alone monitoring system. With the use of analog to digital converters,
this system can communicate with existing PLC/DCS systems. If a PLC/DCS does
not exist, CMCP can create a custom Wonderware HMI system to meet the customers exact needs.
Typical Installation Will Include:
For
additional information on Turbine Supervisory Instrumentation please view
the CMCP Application Notes:
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