Power plants periodically require performance testing to verify proper operation and pinpoint areas for improvement. However, performance testing requires specialized expertise and experience, and quite a bit of judgment. This is why power plant personnel usually don’t attempt to do this type of testing themselves, but instead rely on expertise provided by either a dedicated internal team or a third-party company.
Introduction
One of the first decisions for any test team is determining just how many additional points of measurement are needed and at precisely what locations. In some cases, it’s not possible to insert an instrument at exactly the desired point of measurement, so judgments must be made as to the best approach.
More measurements result in more data and potentially better test results, but there is a cost to adding additional instruments, so tradeoffs must be made. The lower the cost of adding each instrument, the easier it is to make these types of tradeoffs.
The next step is to install test software on a computing platform, usually a PC. Once all instruments are installed and working, the output from each is connected to the PC. Connections are also made to deliver data from existing instruments and other sources to the PC.
Once all data is connected to and available at the PC, the test software can process the data and produce results. But performance testing requires much more than just crunching numbers, because test personnel must be able to spot data inconsistencies, instrument errors and other issues. They must also be able to interpret the results, and in some cases install additional instruments to measure more variables.
One of the first steps for a performance test is the installation of additional instruments, a difficult task with traditional wired solutions.
Issues with Wired Infrastructure
Performance testing requires the installation of instruments to measure parameters such as flow, pressure, temperature and power in steam and gas turbines, coal- and gas-fired boilers, cooling tower pumps and fans and metered steam flow systems. Instruments are installed in each of these areas and connected to the plant’s control and monitoring systems, and data from these instruments is used in performance testing.
In many cases, there are challenges associated with the use of wired instruments for performance testing. These include the labor, expense and time required for installation; conversion of the analog signals from the instruments to digital; and possible damage to the long power and signal wires that run across the plant.
Labor expenses and time required for running wires can be excessive, but a bigger problem is often the expense and time required for debugging analog-to-digital conversion and other issues. And the longer the wire runs, the greater the likelihood of damage to wires and replacement of connectors and fuses. These issues create pressure to reduce the cost and time of performance testing.
Years of experience has proven that there is no viable way to substantially reduce the issues associated with wired instrumentation and its related infrastructure, so a solution is needed to replace wired with wireless instruments.
Deploying a Wireless Solution
Major utilities have been using WirelessHARTTM instruments for years in permanent installations across plants and facilities with great success, so it is natural for them to investigate their use in the temporary installations required for performance testing.
WirelessHART can be thought of as the HARTTM digital communication protocol without wires, although it can communicate much more data than the standard HART protocol. It is an International Electrotechnical Commission (IEC) 62591 industry standard, with wide acceptance and use worldwide. It’s easy to use, and its mesh technology enables the automatic establishment of communications between each WirelessHART instrument and one or more gateways.
For performance testing, only one gateway is required, and it can be hardwired to the PC using Ethernet and the ModbusTM TCP/IP communications protocol.
A combined cycle gas turbine generating unit with a heat recovery steam generator requires about 60 points of measurement, with 32 of these measurements made using wireless instruments, and with each wireless instrument connected to the gateway.
Communications between an instrument and the gateway is typically not direct, but instead is automatically routed through one of the other instruments along an automatically selected and optimal communication path. The other assets can have similar setups for wireless measurements, although fewer points of measurement are required. These points of measurement are typically spread across a wide area of the plant or facility, one of the main factors favoring wireless over wired installations.
Each instrument is installed at the desired point of measurement, with no wires required for power or for connection to the gateway. Each instrument automatically connects to the gateway and is quickly recognized. Data from the instrument is then sent to the PC-based performance testing software at selected intervals, typically once per second.
Benefits for End Users
Upgrading from wired to wireless instruments reduces field labor substantially, about 40 percent for gas turbine testing and by 15 percent for cooling tower testing. For quarterly verification of metered flows at cogeneration plants, for example, wireless instruments allow three separate tests to be combined into one, cutting field labor by 25 percent. With wired instrumentation, these would have to be run independently because test areas are normally widely dispersed. With wireless, all tests can be setup and run at the same time from one central location.
These field labor cost reductions are very conservative, as they assume no problems with wired installations, which is typically not the case. Reducing field labor costs produces a corresponding reduction in test setup time, from weeks to days in many cases.
A WirelessHART plant performance monitoring system allows utilities to reduce the cost and time required for testing procedures. These savings also allow them to perform additional types of performance tests on equipment such as steam turbines and heat recovery steam generators, leading to improvements in the operation of these critical assets.
To further improve testing, utilities can add additional points of measurement in locations not feasible for the temporary installation of wired instruments, such as at the stack of a heat recovery steam generator.
For more information, please visit the FieldComm Group website.
