Real-time networked condition monitoring has now been in full operation at PECO’s Peach Bottom station since 1996. In that time it has cut costs at start-ups and reduced crisis analysis time by some 85 per cent by enabling operators to concentrate on the real issues, and not imaginary problems: it has provided insight into reality.
Advanced condition-based maintenance systems have been in operation at the Peach Bottom Atomic Power Station since the end of 1996. Since that time we have been able to make significant savings across the board and continue to reap these benefits. One of the interesting effects of installing such systems has been their use in what might be termed ‘negative diagnosis’; using the system to prove where the problem is not, and hence allowing engineers to focus more quickly on the real causes of the problem.
PECO Energy is a Philadelphia-based investor-owned utility company operating eight power plants in south-eastern Pennsylvania and north-east Maryland, generating electricity for some 1.5 million consumers. The utility has a reputation for technical innovation. The real-time vibration-based condition assessment system at Peach Bottom is one of the world’s largest such installations.
Peach Bottom is a boiling water reactor plant driving two 1150MWe GE units that produce 25 per cent of the utility’s total capacity.
The plant, commissioned in 1974, represents a $1.2-billion capital investment. Each of the two reactor vessels is over 22 metres high and 6 metres across and houses 764 uranium dioxide fuel elements and 185 boron carbide control rods. Feed pumps supply water to each reactor, producing over 14 million pounds of steam an hour at 290°C and 1035 psi to drive the turbine/generators before being passed to condensate and recirculation pumps. The turbines are almost 90 metres long with a speed of 1800 rpm, producing 33 kA at 22 kV.
In 1992, a thorough reliability-centred analysis of the condition monitoring systems was conducted, resulting in the update project now in progress.
The review identified:
Perhaps the most important problem – and the key to achieving insight into reality – was that the analysis system was unable to correlate the various plant data, making it unable to relate vibration level changes to pressures, temperatures and flow levels. The decision to install a Solartron 1051-based networked vibration information system (NVIS) was taken in 1994; installation started in mid-1995 and was completed late 1996.
The strategy was to increase plant safety and equipment availability in an era of corporate downsizing. Three primary objectives were stated:
In business terms, it was necessary to show significant cost/benefits within a single two-year refuelling cycle, with payback in under five years, representing a 20:1 cost benefit ratio. The plan identified major O&M savings and reductions in the number and duration of planned and unplanned outages amounting to over $60 million savings in the 20 year planned plant life – well above the return criteria – with immediate savings of $50 000 in instrument cabling and installation costs from the chosen design.
The situation today
The NVIS system incorporates alarm and trip contacts for the main turbine/generator, and the reactor feedpumps and turbines, and collects, stores, analyses and displays vibration data for predictive maintenance on these units plus the condensate and reactor recirculation pumps/motors. A backup machinery monitoring system monitors the main turbines and the reactor feed pump turbines, and provides alarm and trip functions independent of the computer network. This arrangement prevents computer or network failures from either initiating or preventing a main turbine or reactor feed pump turbine trip.
Most of the computerized data acquisition systems in Peach Bottom are now integrated, encompassing over 270 vibration analysis channels concurrently diagnosing 18 separate pieces of rotating equipment. An essential part of the design was to import and export data to other plant monitoring systems.
The NVIS system is integrated into the existing Peach Bottom Data Acquisition System Ethernet ‘backbone’ which links various plant areas to a communications panel in the main control room. NVIS continuously monitors and analyses the plant across the existing data acquisition infrastructure – many of the new cables were installed in existing trays, saving cost – routing vibration data to the existing plant computer, and extracting related operational data.
A tribute to standardization
Any power station is inherently noisy electrically and so fibre optic Ethernet cabling is installed to ensure EMI (Electromagnetic Interference) immunity. This also provides an open architecture networking platform as well as ensuring high data reliability, simplified cable pulls and reduced power drain. The whole NVIS upgrade – including installation of the 1051 on-line condition monitoring systems – is an excellent demonstration of the benefits of standardization.
Solartron’s 1051 is built on a VMEbus-based hardware platform, UNIX/OSF operating systems with X-Windows/MOTIF graphical interfacing, and OSI and TCP/IP networking. Seven 1051-based subsystems at Peach Bottom feed data via Ethernet to the workstations, provide extensive signal and data processing and significantly reduce the processing load on the central host system.
Each 1051 provides up to 64 parallel dynamic analyser channels and 120 static analog or digital data acquisition channels, enabling it to relate machinery vibration levels to plant status and other static parameters, such as temperature, pressure and flow. This is the key feature that facilitates integration of the complete condition monitoring system, providing invaluable information during plant run-up, on-load and coast-down states. An important strength of the 1051 is its ability to acquire, simultaneously, vibration data from multiple rotating shafts and static plant data in parallel with processing spectra. This power, combined with the machine life-cycle database of critical plant equipment built by the 1051, simplifies fault diagnosis, helping detect and identify potential equipment problems well in advance, avoiding unnecessary shutdowns and optimizing the use of scheduled downtime.
Insight into reality
Plant operators are provided with a machine-state sensitive graphical interface which enables them to be directly involved during run-up, coast-down and on-load. However, the operator environment is strictly for viewing data and other important system parameters; no configuration changes can be made to NVIS while in this mode. The password-protected graphical environment for the vibration analyst provides a powerful software toolkit – including user-configurable alert and alarm functions, data management and a wide range of advanced analytical displays – with which to assess machine condition and diagnose problems. For example, the traditional orbit plot – frequently used to investigate shaft instability – can become cluttered; the 1051’s ‘filtered’ orbit plot removes unwanted information, providing an uncluttered display and allowing analysts to focus clearly on specific machine problems; a clear example of insight into reality.
Perhaps the most powerful view of reality comes with 1051’s multi-plot display, enabling the current and historical behaviour of similar pieces of equipment to be compared side-by-side. It can highlight hidden relationships between seemingly unrelated vibration and static plant parameters, such as interactions between turbines and auxiliary equipment. For instance, there was a problem with a machine at the outboard pump bearing; the multi-plot allowed the outboard pump shaft orbits from three similar pumps to be compared side-by-side, immediately highlighting the differences in each pump.
A primary objective was to replace the shaft cracking monitoring facilities on the vertical reactor recirculating pumps. The 1051 has expedited our ability to recognise shaft crack growth, and to record and document dynamic response information for on-going comparison.
The first real savings came from finally tracking down the cause of a repeated intermittent high vibration trip on a reactor feedpump which had been a persistent annoyance. Examination of the vibration data identified it was operating too close to its first critical frequency. This has now been incorporated into plant operating procedures. Following this, the system provided early indication of a failing primary probe on a reactor recirculation pump, enabling pro-active maintenance to be scheduled in good time and avoiding a critical alarm-induced trip.
A classic area for cost savings is turbine restart following a maintenance outage, and here the 1051 has proven invaluable. Start-up procedures called for turbine rotor bow elimination procedures; on-line real-time vibration monitoring via the 1051 has enabled us to eliminate this requirement and cut four hours off run-up times, saving $85 000 each time.
Key to the efficiency improvements made at Peach Bottom is the ready availability of data in an immediately useable format. Plant operators have a significantly improved picture of the equipment’s mechanical health, and vibration analysts have access to machinery data from any point in the office building – even from home. The system’s on-line ‘study process’ gathers real-time and historic data into a workbook of plots and observations, allowing the creation of application-specific screen displays to simplify repetitive tasks. Additionally, the facility to ‘cut-and-paste’ almost any on-screen information into an on-line engineer’s notebook streamlines the production of reports.
It is the immediate availability of useable performance data that allows diagnostic analysts to resolve crisis events in a short time, enabling them to quickly eliminate the unlikely and just focus on the likely. Here, the 1051 is being used to disprove that a piece of equipment is failing. A recent incident on the recirculating pump set will provide an illustration. The pump set alarm tripped. Immediate examination of the 1051 data showed no problem and so it was decided to bring the pump back on-line and search for the problem elsewhere. The cause was eventually traced to a circuitry problem on the alarm trip. The real benefit was that the 1051 data provided a focus on reality, enabling time to be spent on solving the real issues. Overall, the 1051 systems have provided a dramatic improvement in troubleshooting decision support, reducing analysis time during a crisis event by some 85%.
Work smarter not harder
The systems at Peach Bottom are not complete. Like most businesses we are updating our operating systems to eliminate the Y2k problem. Coincidentally, this will enable MIMOSA-compliant systems and procedures to be adopted more easily in the future. Moving towards MIMOSA (the Machinery Information Management Open Systems Alliance) standards would allow the exchange of common-format files containing, say, vibration, oil tribology, corrosion and thermographic monitoring information between data acquisition and analysis tools could advance our maintenance techniques further and faster.
Static data collection will also be expanded by integrating additional Solartron IMPs (isolated measurement pods) into the network. One target for these IMPs will be a high pressure injection pump for make-up water. This pump is only used occasionally but is stringently tested every quarter to ensure it will function immediately when needed. Installing the IMPs will enable the test data gathering and reporting to be better automated, eventually allowing the tests to be eliminated completely using data gathered during in-use periods.
Other planned enhancements include integrating with more plant-wide systems – particularly the asset and maintenance management systems – extending data correlation into an even wider realm. Advanced operator screens will be developed to further automate equipment condition assessment, enabling plant personnel to recognise abnormal trends easier and alert analysts more quickly and efficiently.
These operator screens will be tied in with more comprehensive alarm monitoring facilities – enhancing control room visibility – and the creation of an ‘engineering desktop’ that will enable almost live static and vibration data to be viewed virtually in real-time from anywhere in the world.
Too significant to ignore
Condition monitoring and analysis in utility power plants, a technology which promises great economic benefits in plant operation and maintenance, is now extensively applied at Peach Bottom Atomic Power Station. While plant managers were initially hesitant to accept some of the more advanced facilities, the reduction in maintenance overheads and overall increase in efficiency is becoming too significant for investor-owned power plant operators, such as PECO, to ignore.