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Microturbine Testing Microturbines are increasingly being used at various consumer sites to generate 480 VAC, three-phase electrical power, typically in the range of 25 to 500 kW. They are relatively small, combustion-gas turbines that run on natural gas, hydrogen, propane, diesel fuel, landfill gas (methane), and even some bio-diesel fuels. The turbines come in two varieties, simple-cycle and recuperated-cycle. Simple-cycle turbines are about 15% efficient, compared to turbines with reliable recuperators (that is, no moving parts) that double efficiencies to nearly 33%. They reintroduce exhaust heat energy into the cycle instead of wasting it. Better yet, system efficiency can reach 85% with an integrated combined heating and power (ICHP) installation. Because they are about the size of an industrial refrigerator, microturbines can easily be installed on site and power a modest-sized building such as a convenience store. When multiple units are interconnected, they can offset the energy expenses and demands of larger facilities such as motels or large apartment buildings. Moreover, some users can sell their excess power back to the grid. Exceptional Efficiency A large market for the generated power and clean exhaust heat includes hotels and other installations that consume both power and heat, known as Combined Heating and Power (CHP) applications. This is the most efficient system. A typical installation employs a heat exchanger on the microturbine’s exhaust, which preheats water for a boiler. Less fuel is then needed for the boiler, and the microturbine system efficiency can reach 70 to 90%. Because of this, new, green energy-efficient buildings are increasingly using microturbines and have been working extremely well with remarkably low emissions. For example, one greenhouse application feeds the exhaust directly to the plants to supply warm, CO2-rich air. Other applications include hybrid-electric city busses, offshore oil-drilling platforms, and farms where fermenting waste tanks provide the fuel gas for operating the microturbines. Vibration TestingDan Lubell, Principal Turbomachinery Engineer, and Jon Wade, Senior Rotordynamics Engineer, use IOtech ZonicBooks with eZ-TOMAS to monitor and record the microturbines’ vibration levels during both production and development testing to ensure they remain within the design envelope. They also test production units in such a unique way that only the eZ-TOMAS software can satisfy their needs for analyzing rotating machines. Because the microturbines run at extremely high speeds, acquiring test data is critical to ensure that vibrations are not dangerously out of tolerance and cause the microturbines to fail. The ZonicBook measures and records synchronous, sub-synchronous, and super-synchronous vibration, which is at, above, and below running speed. The eZ-TOMAS has a built-in feature for condition monitoring alarm levels. It contains a unique, complex speed-vibration matrix, which applies constantly changing pass/fail criteria based upon the speed and time-at-speed operating point of the engine. A “Production Test Report” provides a final look at the engine as the data are summarized on a formatted output page. No further data processing is needed. IOtech ZonicBooks were selected over another stand-alone system that Lubell and Wade were already familiar with, initially because the other instrument was unable to measure turbine speed over 60,000 rpm. “In the beginning,” says Lubell, “we had to use some basic FFT analyzers in the test cell, and a person had to manually set up the instrument and watch it constantly; they were essentially stand-alone units with no software capability. We decided to upgrade the setup and find a new solution. In contrast to basic FFT analyzers, the ZonicBook records continuous vibration data, contains built-in FFT software, easily records the turbines’ top vibration levels, provides the added safety of an automatic shutdown, and prints out a record, all for one-half the price. We found the system to exceed our expectations.” Lubell and Wade use from one to eight channels to monitor very high-frequency rotor vibration levels that could reach several thousandths of an inch on each microturbine. Proximity probes are located near each oil-free air bearing that supports the rotor. The eZ-TOMAS software for monitoring and recording multiple channel vibration lets them analyze the proximity probes’ output amplitude, frequency, and phase in real time and compare both synchronous and asynchronous peak amplitudes in different locations to the complex pass/fail criteria, as well as the automatic shutdown limits. Hands-Off Testing “When we first started looking for equipment like this, I bought one of the earliest model ZonicBooks, tested it with the eZ-TOMAS software, and I found that it did more than the other instruments I had worked with and new ones that I evaluated. However, over time, we came up with some ideas that would help us even more — to enable a higher quality process — and we passed them on to the IOtech software engineers. They are very supportive. We would make a request for a new feature, and they would provide it in a couple of weeks, or sometimes just in hours. We are confident now that we can run the tests in an unattended cell because of all these improvements and upgrades. We are very pleased because we got the product we needed when no one else had it.”
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[ IOtech PC-Based Data Acquisition (DAQ) and Instrumentation - PDF Format IOtech PC-based products (USB, PCI, Ethernet, GPIB) and signal conditioning options capture waveforms and measure most physical parameters including temperature, vibration, strain, velocity, acceleration, position, as well as common voltage, current, power, and data logging. IOtech's solutions are used in environments such as |