Guide to Configuring a Fiber Optic Sensing System

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Power Generation Applications  -  DAVIDSON POWER      

Combustion Dynamics Monitoring Systems

Davidson offers a line of general use fiber optic transducers and signal conditioners that together measure pressure, temperature, vibration, load, and displacement. For general use applications, these transducers and signal conditioners can be multiplexed and configured in a variety of ways to create a sensing system.  In addition to the components of a general use fiber optic sensing system, Davidson has developed product lines that are specifically tailored for process control, power generation, and oil and gas production.

Call us at 877-656-4900 to discuss your most demanding needs!

Process Control Davidson Process offers fiber optic transducers that measure pressure, temperature, level, and flow.  The systems are suitable as form-fit-function replacements for existing electronic transmitters and can be fitted for intrinsically safe installations.

Power Generation Davidson Power offers customized transducers with integrated signal conditioners for a variety of applications including combustion dynamics monitoring in gas turbines and monitoring of the combustion cycle/compression cycle in industrial engines and compressors.

Oil & Gas Production (Davidson Energy, Inc) Davidson Energy offers downhole point pressure and temperature measurement sensing systems, i.e. transducer and signal conditioner.  Davidson's system operates at temperatures to 500ºF, pressures to 20,000 psi, and at transmission ranges to 15km.

Combustion Dynamics Monitoring Systems
 

Large power generation gas turbine engines must operate outside stable stoichiometric limits to minimize emissions and operate efficiently.  Dynamic instabilities during the combustion process cause severe stress and potential damage to the engines. Advanced combustion monitoring systems can be used for on-line tuning and to maintain dynamic stability, minimize emissions, and detect problems.  Early detection can enable the operator to avoid  serious trouble or catastrophic damage to the engines.

Davidson offers a line of combustion dynamics monitoring systems customized for Siemens 501G and General Electric E and F series gas turbines. These turnkey systems include all of the transducers, cable, and signal conditioning needed for a fully integrated combustion dynamics monitoring system.

CDMS-7FA system is designed for use in General Electric 7FA gas turbines.

CDMS-7E system is designed for use in General Electric 7E / 7EA gas turbines.

CDMS-501G system is designed for use in Siemens 501 series of gas turbines. 

These systems offer the following performance specifications:

Frequency Response                 2 Hz to 5 kHz

Dynamic Range                        46 dB

Transducer Temperature Limit    1000° F

In the past, combustion dynamics monitoring systems utilized piezoelectric transducers with “infinite” tubes and associated purging systems. With Davidson fiber optic transducers, the infinite tubes and all of the associated purging systems can be eliminated.
 

The CDMS-7FA, CDMS-7E, and CDMS-501G systems integrate spectrum analyzer with state-of-the-art Davidson fiber optic transducers.  Davidson fiber optic transducers can tolerate temperatures up to 1000° F continuously and can be placed very near the combustion zone in the turbine.  The result of this direct measurement is higher quality signal with lower installation and maintenance cost.  The CDMS-7FA, CDMS-7E, and CDMS-501G systems are the best value for combustion dynamics monitoring.

These monitoring systems provide crucial information that turbine operators can use to tune the engines and this enables high operating efficiency and low emissions.  Moreover, the combustion dynamics signals provide insight into the health of the engines that may enable avoidance of costly maintenance or catastrophic failures and may even result in lower insurance premiums. 

Davidson provides a turnkey system including installation, commissioning, and training of site personnel.  For fleet applications, Davidson plans to offer an on-line monitoring service to assist with report generation, analysis of trends, and comparisons with other assets.  This collaborative service will allow operating personnel to discuss any situation with a combustion dynamics expert.

 

SYSTEM CONFIGURATION

 
A typical CDMS consists of the following major subsystems:

• Fiber Optic Pressure Pulsation Transducers with cabling specific for the turbines

• Fiber Optic Signal Conditioner

• Spectrum Analyzer

• Dynamic Monitoring System

Figure 1 – CDMS-7FA System Schematic

SUBSYSTEM DETAILS

 
Fiber Optic Transducers - Davidson fiber optic pressure pulsation transducers are designed for installation in the turbine casing where the existing pressure outlet tubes are installed.  The transducers housings are designed to be installed flush with the inner liner.  The transducers are tolerant to moderate misalignment of the threaded hole in the casing and the drilled hole in the liner of the General Electric turbines.  For the Siemens turbines, the transducers have been designed with flexible probes  insertion and adjustment flush with the end of the "J" tubes.  The transducers have 50 feet of fiber optic cable rated for 550° F with stainless steel overbraid for mechanical protection and rugged simplex connectors for ease of field installation and replace if necessary.

Figure 2 – GT1200-7FA Transducer Housing

Fiber Optic Signal Conditioner - The fiber optic signal conditioner sends a continuous beam of light to each of the transducers via the fiber optic cable.  Each of the separate light signals is modulated by the transducers and reflected back to the signal conditioner where it is converted into an electronic signal that is further processed by a microprocessor. The microprocessor in the signal conditioner converts the signals at sampling rates of 100 kHz. The microprocessor converts the signal into an analog output signal, i.e. +/- 5 Volts, proportional to the pressure.  The result is unprecedented measurement accuracy and frequency response in harsh industrial environments.

 

Spectrum Analyzer - A commercial spectrum analyzer and five-hundred feet of military-grade duplex singlemode fiber optic cable is typically included with the system.  The simplex fiber optic cable is terminated on each end and is routed from the turbine electrical cabinet to a fiber optic switch in the control room for connection to the monitoring system.  The simplex fiber optic cable is typically routed through the existing cable trays and enters the control room at a location to be determined at the time of installation.

Monitoring System and Software - The monitoring system consists of an industrial rackmount computer and a 17” LCD display for each turbine in the fleet.  The computer receives the signals from the turbines and displays the signals according a variety of options to be defined during the training session prior to installation.   Setup entails a normal computer configuration with a TCP/IP address that can be connected to the plant network and provides Virtual Private Network (VPN) access to external users. 

 

The monitoring software consists of the following:

• Basic Combustion Measurements - This package provides the basic combustion analysis software and allows the user to configure the display to provide a visual representation of the engine, to set thresholds for alerts and warnings, and to enter calibration constants for the transducers.

• Criteria Trending - This package provides the trend analysis software and allows the user to detect long term changes in the frequency spectrum of each combustor.

• Data Miner - This package provides the software necessary to extract data from the system archive in a variety of ways for further analysis.

• One-way MODBUS Slave Interface - This package provides a serial interface and necessary software to interface the CDMS system to the control system.

INSTALLATION, COMMISSIONING, AND TRAINING

Davidson provides turnkey installation, commissioning, and training for the system operators.  Consider the following when developing a plan for installation of a CDMS:

• A pre-site conference call should be conducted to walk through the installation identifying the need for penetrations, permits, power, special needs, etc.

• The turbine must be shutdown and cool at the time the transducers are installed.

• The turbine must have adequate alignment and clearance between the threaded the casing and the inner liners on GE turbines and along the "J" tube for Siemens turbines. 

• It is best to route the new fiber optic cables along existing cable trays.

• Electrical power needs to be available at the location of the monitoring system and the fiber optic signal conditioners.

• On-line or remote monitoring requires a broadband internet connection with the monitoring system.

• For planning purposes, assume that installation and commissioning can be accomplished by two technicians in two work days.

• Training in the use and setup of the system should be scheduled immediately after installation to minimize the delay in the use of the system after commissioning.  The training should be planned for completion in two eight-hour days at the customer site.