One characteristic common to many electric utility companies is the mix of sizes and technologies at the utility’s various plants. This means efforts to improve performance and reduce costs can vary from plant to plant. For personnel undertaking such improvements, the tools must be flexible so technicians can measure baseline performance and implement improvements easily and quickly. The testing required to verify proper operation and pinpoint areas for refining or upgrading will be different than that needed for checking condenser cooling towers versus turbines.
Evaluating the performance of a major power-plant equipment asset usually involves utilizing a number of instruments to measure strategic aspects of the asset’s function. And, while it is a good idea to have these instruments on a permanent basis, it may not be cost effective. This leaves the power plant’s evaluation team with the task of deploying them temporarily during the actual testing efforts. Installing these can cause some challenges.
As an example, one major electrical utility has maintained an evaluation program since the early 1980s. It formed a dedicated generating-plant performance team to provide specialized testing and analytical services. The team used heat rate to benchmark performance. Heat rate is a common measure of cycle efficiency in a steam-cycle power plant. It is equal to fuel heat input divided by electrical output.
Troubleshooting was an issue because temporary wiring often failed intermittently in operation. When such failures occurred, excessive troubleshooting time and a high level of expertise were required to determine the root cause. As the team got used to saying, “Technicians install the wiring, and engineers troubleshoot it.”
To address these concerns, the team adopted WirelessHART for instruments temporarily installed to perform gas turbine and cooling tower tests. The wireless units also were used to verify the accuracy of the cogeneration unit steam measurements. By avoiding much of the complex wiring normally required for this type of temporary installation, the team estimates it saves 15 to 40 percent of setup time.
Modern wireless technology allows the team to perform more than 100 tests and performance evaluations each year. The experience gained adds to an extensive database of documenting past performance challenges and solutions. According to the power plant performance team, it would not be able to perform as much testing with conventional wiring due to the high amount of labor, installation, troubleshooting and decommissioning time needed for the wired infrastructure.
Mechanics of Testing
Performance testing requires specialized expertise, experience and quite a bit of judgment. When assessing an installation, one of the first decisions for a test team is determining how many additional points of measurement are needed and where. In some cases, it is not possible to insert an instrument at the exact desired point of measurement, so judgments must be made to find an alternative.
The additional measurements yield more data and — potentially better test results. Of course, when testing, there is a cost to adding each instrument. Using wireless instruments eliminates much of the wiring costs and allows the team to add more instruments without exceeding the budget.
Test technicians routinely install instruments to measure parameters such as:
- Flow, pressure, temperature and power in steam and gas turbines.
- Temperature and pressure in coal- and gas-fired boilers.
- Power consumption and mechanical component condition in cooling tower pumps and fans.
- Flow in metered steam systems.
The test software usually is installed on a PC, which interfaces with all the special instruments and the plant’s automation host system. Before wireless instrumentation was available, technicians needed to run temporary wiring for data acquisition. This cumbersome practice was difficult to install and manage because this wiring did not use cable trays and was strewn throughout the plant (figure 1).
Once all data sources were connected and available at the PC, the test software can process the data and produce results. Performance testing requires more than just crunching numbers, however. The test technicians need to spot data inconsistencies, instrument errors and other issues. They need to interpret the results and, in some cases, install additional instruments to measure more variables if the required information to make decisions was not available.
FIGURE 2. WirelessHART is a self-organizing network, so it requires a minimum of setup time and network management.
Resolving Wired Infrastructure Issues
Before WirelessHART, adding instrumentation was complex. Associated costs and complications included labor expense and the time required for installation, conversion of analog signals from the instruments to digital, and possible damage to the power and signal wires running through the plant.
Labor expenses and the time required for running wires was high, but they usually were predictable. The bigger problem in many cases was the expense and time required for troubleshooting and debugging analog-to-digital conversion and other issues. Electricians could run wires, but more expensive engineering time was required for troubleshooting. Unfortunately, at the time, these problems were simply accepted as part of the process and unavoidable.
At the electric utility, the company pressed for a more efficient solution. Company management asked the plant performance team if they had any money-saving ideas. The utility had been using WirelessHART instruments for some time in permanent installations — across many plants and facilities — with great success.
It was, therefore, natural to consider investigating the use of wireless technologies in the temporary installations required for performance testing. WirelessHART can be thought of as the HART digital communication protocol without wires. WirelessHART, however, can communicate more data than the standard HART protocol. For the testing team, the setup was simple because only one gateway was required to interface to the wireless instruments. It was hardwired to the PC using Ethernet and Modbus TCP/IP.
FIGURE 3. One gateway has been sufficient for communications with all temporary instruments at each installation.
Case in Point: Testing Turbines
As a case in point, consider one of the complex installations found at power plant. Evaluating a combined-cycle gas turbine (CCGT) generating unit with a heat recovery steam generator typically requires about 60 points of measurement — with about half of the instruments using WirelessHART. These devices form their communication path to the gateway automatically because WirelessHART uses a self-organizing mesh network (figure 2). Some communicate with the gateway directly while others create links with adjacent instruments.
The best gateway location usually is in a high position — away from walls and large steel structures — so there is a clear line of sight from any direction (figure 3). With this simple approach and the self-organizing capabilities of WirelessHART, communication problems are rare. The radio signal is resilient, and the meshing action also helps a network cover a large area.
At the power plant, though some instruments still required wiring, upgrading from wired to WirelessHART instruments reduced field labor substantially: about 40 percent for gas turbine testing and 15 percent for cooling tower testing.
For quarterly verification of metered flows at cogeneration plants, wireless instruments allowed three separate tests to be combined into one. This reduced field labor by 25 percent. By contrast, when the test had been run with wired instrumentation, the three tests had to be run independently. (The test areas were widely dispersed among different areas of the plant, making it too expensive to run wiring.) In all, reducing field labor costs resulted in reduction of test setup time from weeks to days, by conservative estimates.
Though the test team did not have the time to perform any site surveys or configure the instrument placement for optimal radio communication, wireless communications between the gateway’s integral antenna and each instrument were surprisingly robust. (Placement was chosen for testing convenience.) This demonstrated quick setup and proved the robustness of the WirelessHART technology.
The WirelessHART plant performance monitoring system allowed the utility to reduce the cost and time required for each test. With more available time, it can perform additional types of performance tests on equipment such as steam turbines and heat recovery steam generators. This can lead to improvements in the operation of critical assets.
To improve testing, the company plans to add additional points of measurement — such as at the stack of a heat recovery steam generator — in locations not feasible for the temporary installation of wired instruments.
In conclusion, using WirelessHART to modernize plant performance monitoring can help a utility expand its testing and asset-management programs. As wireless sensing technology continues to penetrate industrial facilities for process and equipment monitoring, there are more types of instruments that can be added permanently to production assets— turbines, cooling towers, pumps and even individual steam traps — to diagnose and improve performance continuously. These instruments can use an existing WirelessHART network and can be used to perform many of the same tests an evaluation team would — but on a continuous basis. This allows the team to concentrate on the highest-value assets.
WirelessHART is a useful tool to evaluate and improve performance. It has the potential to recover additional revenue for any utility as well as provide a public good by reducing the carbon footprint through increased efficiency. PC