By Scott Abramson, Reliability Manager, Duke Energy Generation Services
In the reliability world of utility businesses, CBM typically refers to condition-based maintenance or condition-based monitoring. In reality, performing conditioned-based monitoring helps those charged with conducting condition-based maintenance. This philosophy should be looked at as homogeneous across utility assets when the organization is seeking long-term reliability of an asset. This is especially true when the organization depends on the health of its assets to provide long-term revenue generation.
Today, more utility businesses are adding a mix of renewable assets to their traditional generation fleets. The same CBM philosophies that apply to traditional assets hold true for renewable assets. In many cases, however, asset owners have been slow to support, fund and install CBM equipment.
Condition-based monitoring equipment encompasses several different types of instruments and monitoring equipment. The most common devices sense vibration levels, oil contamination, temperatures and pressure changes. Some equipment monitors all of the above. Many asset operators have developed their own customized tools for monitoring equipment condition. Duke Energy Renewables, part of Duke Energy’s commercial businesses, is one of them. Duke Energy Renewables’ reliability group developed an in-house performance monitoring tool that complements the traditional CBM equipment.
Among all contemporary renewable forms of energy generation, wind power possesses many similarities with conventional generation. For example, wind turbines and steam turbines both involve rotating shafts and load-carrying bearings, as well as all the axial and radial forces that accompany the dynamics of these moving parts. For years, generation facility owners have used vibration monitoring equipment on rotating equipment to monitor asset health. The decision to equip 500 to 1,200 MW steam turbines with condition monitoring equipment has historically been an easy one for asset owners.
The speed at which renewable asset owners have adopted the concept of CBM and funded equipment installations is rather puzzling, particularly to those in an organization charged with optimizing asset reliability and productivity. For wind turbines that sit nearly 300 feet in the air and endure intense stress during rotation, the decision to install some type of CBM equipment hardly seems debatable.
The business case for installation of CBM equipment on wind turbines begins with the gearbox. As an integral part of the wind turbine drive train, gearboxes withstand constant stresses exerted on their internal components, which consist of gears, bearings and shafts. The gearbox is considered the workhorse of the drive train with a typical low-speed rotation of 15 rotations per minute (RPM) and a high-speed rotation of 1,800 RPM. This mechanical mesh translates into a 118:1 ratio from the three different stages and approximately 382 combined teeth of gears.
The business case for installing CBM equipment on wind turbines becomes much stronger when cost comparisons are made between potential catastrophic failure of an asset and the upfront cost of CBM equipment installation. The typical gearbox replacement ranges from $100,000 to $250,000. Gearbox removal, along with installation of a new unit, necessitates the use of a crane, too. Complete gearbox replacement, including equipment, crane time, labor and lost megawatt generation, can easily approach $500,000.
As a result, the cost of one wind turbine gearbox failure would be enough to make the asset owner wish he or she had invested in a vibration monitoring/CBM system. Oftentimes these systems are packaged with accelerometers, cabling, signal converter box and software for data collection and analysis.
According to a May 2010 Renewable Energy World magazine article, gearbox failures account for the largest amount of downtime, maintenance and loss of power production at U.S. wind farms.These costly failures can approximate 15 to 20 percent of the price of the turbine itself, making wind turbine gearbox monitoring a virtual necessity. The article validates the notion that most gearbox failures are preventable and often result from improper lubrication and lack of routine maintenance.
Making the decision to embrace CBM is only the first step. Next, the asset owner must develop a request for proposal (RFP) document and circulate it among potential bidders. Doing so affords the asset owner an opportunity to specify details that suit their particular circumstance and encourages bidders to propose a system that is appropriate and suitably adaptable.
Once the bidding process is complete, the next step is to develop a selection matrix to help methodically identify the system and vendor that best meets the organization’s needs.
Duke Energy Renewables installed General Electric Wind Energy’s condition-based maintenance monitoring system at several of its wind farms, which are located in Colorado, Pennsylvania, Texas and Wyoming. Together, Duke Energy and GE Wind Energy set out to boost the reliability of the electric generation at the selected wind farm by exploring and implementing next-generation wind turbine technologies. Duke Energy personnel are true believers in the value of CBM, as evidenced by their decision to procure the GE Bentley Nevada ADAPT wind condition monitoring solution for the selected project in early 2010. This decision represented the first phase of a proactive asset monitoring and health management program. The Duke Energy team worked with the GE and Bentley Nevada experts to understand the technology and the capabilities offered by the ADAPT wind condition-based monitoring solution.
Duke Energy has already seen benefits over more than a year of using the GE condition monitoring system at our Campbell Hill Windpower Project near Casper, Wyo. Data gathered from accelerometers installed on one of the wind turbines indicated anomalies in the waveform displayed in the enveloping spectrum. The spectrum waveform displayed mechanical impacts that look like spikes or peaks, (typically referred to as amplitude or acceleration). This type of vibration data is typically associated with early signs of bearing failure. The bearing identified was on the high-speed stage of the wind turbines gearbox. This prompted a shutdown and inspection of the high-speed stage of the gearbox. Upon inspection, an inner race defect in the high-speed downwind bearing was discovered. A bearing can be replaced at a fraction of the cost of a total gearbox replacement.
In another case, wind turbine #19 displayed similar signs of high energy waveforms. This time, however, it was on the generator end of the rotating assembly. By catching this bearing before complete failure the repair was much less costly and the downtime for the wind turbine minimized. By proactively addressing conditions identified with CBM equipment, Duke Energy can maintain a high level of availability and reliability, thereby enabling uninterrupted revenue generation from the wind farm.
Duke Energy views CBM as a vital diagnostic tool that helps drive asset performance higher and enables best-in-class operations and maintenance practices. When it comes to boosting productivity, reliability and safety, the capital expenditures for CBM system and equipment upgrades appear to be worthwhile.
Author: Scott A. Abramson has over 30 years of experience in the utility business and has held several responsible positions within Duke Energy. Scott is currently the Reliability Manager for Duke Energy Generation Services and provides corporate support for over 23 generating facilities that consist of renewable generation assets along with fossil generation assets. Scott and his groups’ focus is to maintain a high level of reliability for DEGS assets by exercising proactive measures, which include condition monitoring for achieving an efficient and effective implementation of condition based maintenance. Scott holds an MBA along with several industry recognized certifications that include Certified Maintenance and Reliability Professional (CMRP) and Certified Energy Manager (CEM).
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