ENERGY TORQUE MEASUREMENT APPLICATIONS
ENERGY TORQUE AND POWER APPLICATIONS
TORQUE MEASUREMENT & POWER MONITORING CASE STUDIES
See how customers around the world are using TorqueTrak systems from Binsfeld Engineering to troubleshoot and optimize their machinery, control processes, increase efficiency, prevent damage and solve challenging problems — in short, saving time and money by making smart data-based decisions.
Water Turbine Performance Testing
When Russell Westbrook and Mete Sireli of Clean Current Power Systems needed to do some turbine performance testing, they chose Binsfeld’s TorqueTrak products to help them look for answers. Clean Current ran their proprietary “generator in open circuit” in a tank full of water to determine the total losses of the turbine due to various effects such as “generator cogging”, “bearing friction”, and “viscous losses”.
After completing the water tank tests in their shop, they sent the turbine to the Institute of Ocean technology for testing in their 200m tow tank. Part of this testing included using a hydraulic brake equipped with a force transducer to determine the torque produced by the turbine. They ran the generator in “open circuit” as in the previous test. A known brake pressure was applied to keep the turbine rotational speed constant. Using this information they correlated the brake pressure to the measured brake torque required to run the turbine at a given torque and rotational speed.
The in-house tank tests with Binsfeld’s TorqueTrak Systemand the towing tank tests with a custom built brake-force transducer allowed Clean Current to determine the hydrodynamic performance of their proprietary turbine.
Bending Strain on Wind Turbine Blades
Kenetech Wind Power, Palm Springs, CA – To further optimize the design of their large scale wind turbines, Kenetech design engineers wanted actual bending stress measurements on the blade shank where it attaches to the rotary hub. But how could the signals from the rotating Micro-Measurements strain gages be communicated to the data collection system?
Slip rings were ruled out due to the lack of space and the excessive cost of machine disassembly required for installation on the rotor located 200 feet above the desert floor. Binsfeld TorqueTrak telemetry provided a convenient solution to the problem.
The lightweight telemetry transmitters were carried up the tower and installed on the rotor hub, eliminating the need for a crane. The bending gage data was transmitted from the rotating system to a receiving antenna on the tower and then cabled into the data collection trailer on the ground. Kenetech now had live bending data that they could correlate with wind speed and other parameters to provide key information to improve the turbine design.
Torsional Vibration on Refinery Fan
Engineering Dynamics Incorporated (EDI) performed a field test of an induced draft (ID) fan system at a refinery that was experiencing failures of couplings, flexible disc style. The fan is part of an atmospheric furnace that heats approximately 152,000 barrels of crude per day. The ID fan is driven by a 350 HP induction motor. The motor speed is controlled by a variable frequency drive (VFD) from 0 to 1200 RPM. The trouble began when the motor was changed out for one of similar electrical performance, but of different physical size.
The failure of the original flexible disc coupling consisted of a crack in the spacer, which appeared to originate at a bolt hole. Initially, plant maintenance was blamed for possibly over tightening the coupling bolts. The 45 degree angle of the crack in the coupling spacer is a typical indication of high torsional vibration.
To quantify the transmitted and dynamic torque in the coupling, a TorqueTrak 10K telemetry system from Binsfeld Engineering was used with a Micro-Measurements strain gage. The waterfall plot below shows a torsional natural frequency (TNF) of the system near 58 Hz, which was being excited by 1× electrical frequency of the VFD. This resulted in high dynamic torque in the coupling when operating the fan at 1000 – 1200 RPM.
Coupling Meltdown on Pumping Station
At a crude oil pumping station (consisting of 10 units with 4500 HP/ unit), a problem arose where the elastomeric couplings melted during regular operations as seen in this photo.
Suspecting torsional vibration as the cause of failure, Mr. Gilberto Rios of DYNA company installed the TorqueTrak 10K telemetry instrument and a Micro-Measurements strain gage to measure the true dynamic torque during operation. Shown below are the data. a. Torque. b. Shaft Speed. c. Torsional Vibration Spectrum:
in TEST 6 at 984 RPM, the torque increased dramatically, and showed great oscillation. In the test, the speed was reduced quickly to avoid irreparable damage to the elastomeric couplings.
ANALYSIS & CONCLUSION
The heat produced by vibratory torque resulted in great oscillation which led to such a temperature increase the rubber element of the bearing started to melt. The most likely cause of the failure is due to the interaction between torsional vibration and the operation of the governor. At high loads and speed, the governor can lose stability and excite oscillations.
However, interaction between the governor system and low-frequency torsional vibrations can cause damage to the elastic coupling and/or driven machine. Because improving the performance of the governor at these low loads proved to be very difficult, the solution would be to install an oversized coupling that could deal with the vibratory torque level without exceeding the allowable heat production in the rubber element.
Due to the high cost of this solution, it was decided to limit the engine’s velocity to a maximum of 970 rpm since a speed over this limit will produce very severe torsional oscillation. The units at this oil pumping station have been working for the last months using this set max velocity with acceptable results.
This case study was provided by:
Mr. Gilberto Rios
DYNA Tv 33 136-53
In 24 Bogota 01100, Colombia
Around 20 years in petroleum companies in Colombia, USA, Middle East.
Torque Data Key to Wind Turbine Design & Production
Torque is an important variable to the designers and manufacturers of wind turbine technology. Torque data is especially critical in the evaluation of wind turbine components such as bearings, gears, and braking systems. By providing the true mechanical work being generated by the rotor shaft, torque can be used to determine the true efficiency of the system: mechanical energy in – versus electrical energy out.
In order to collect torque data, a bondable strain gage sensor is applied to the shaft. The strain gage is a Wheatstone bridge circuit that changes resistance in response to distortion of the shaft surface when rotated under load. The relationship between this distortion (strain) and the mechanical work being generated (torque) is linear in the elastic region and based on the physical properties of the shaft. The best way to collect strain data from a rotating shaft is via a telemetry system that reads the analog signal from the strain gage and transmits it as a digital signal to a stationary receiver where it is collected for analysis or used for real-time process control.
The TorqueTrak Revolution system manufactured by Binsfeld Engineering Inc. provides torque, power (hp or kW), rpm and direction of rotation data continuously using inductive power and data transfer. It has been used successfully in many applications in the wind industry, where the typical service life goal for wind turbines is 20 years and meaningful validation trials may last on the order of months or years.
One of our clients tested a scaled-up design of their patented vertical wind turbine for 18 months. The 25-100 kW turbines being evaluated featured unique stationary stators that funneled and accelerated the wind into the rotor blades. “The robust and unique combination of the stator and rotor design allows the turbine to operate in Class 6 and 7 wind speeds (25-30 m/s). Most turbines cut out at 25 m/s,” they said. Our client added that they’ve been using the TorqueTrak Revolution to capture torque data for a publishable power curve. The data will validate the full-size models developed from 1/12-scale wind tunnel prototypes. They also plan to use the results to scale up designs in the 0.25-1 MW range and scale down designs in the 1-5 kW range.
TMA 25 KW VERTICAL WIND TURBINE
The National Renewable Energy Laboratory has also specified the TorqueTrak Revolution as one of over 150 sensors being leveraged to characterize all dynamic motions and loadings on a generic gearbox typically employed in most large-scale turbine designs. The goal of this collaborative effort between the Department of Energy, wind turbine OEM’s, drivetrain component and lubrication suppliers, and turbine owners and operators is the development of a complete mathematical model of the entire system, available in the public domain for the validation of improved gearbox designs.1
Two gearboxes in the 600-750 kW range are being built and instrumented for the investigation. One will be run on a 2.5 MW dynamometer at the National Wind Technology Center and the other will operate in the field on a turbine in the Ponnequin wind farm, both located in Colorado. The TorqueTrak Revolutionallows studying of torque loads when braking on high speed shafts. Occasionally – our customers find that generators may carry torque for a short period of time.
Ensuring quality and reliability is the reason another client in Iowa invested in two test stands for the gearboxes that represent the core of their powertrain. Their 2.5 MW wind turbine splits the torque from the rotor shaft through a multipath, load-distributing design to drive four generators, reducing component failures and extending the operating life.2
TORQUETRAK REVOLUTION SYSTEMS ON GEARBOX TEST STAND
To test production gearboxes, they built two test stands incorporating the TorqueTrak Revolution, one system monitoring torque on each of the four output shafts. The torque signals are fed back to a PLC that controls a hydraulic servo loop regulating rotary actuators that maintain the desired torque load on each shaft. Both regular production and endurance testing have been performed on the test stands. The endurance tests simulated 20 years of operation in 1,100 hours. This method was used because continuous torque data was necessary.
Utilizing torque as part of a condition-based monitoring (CBM) strategy is not currently standard practice in the wind industry. Bearing temperatures, vibration, and oil particulates are commonly measured variables relied upon to monitor drivetrain health. Measuring, and logging, torque data is important to many components – especially at it relates to the gearboxes.
The measurement of true mechanical torque is a key parameter for the wind industry in test stand and design validation applications. It may hold promise as a worthy drivetrain CBM variable in the future. As the examples show, the TorqueTrak Revolution system is an ideal instrument for the continuous measurement of torque in these cases.
THE TORQUETRAK REVOLUTION SYSTEM
The TorqueTrak Revolution delivers continuous torque and power data using inductive, noncontact technology, resulting in long-term, reliable operation. Installation is simple; shaft modification and machine disassembly are not required. It features sophisticated 14-bit signal processing for a precise output signals and many setup tools for easy calibration and scaling.
• W. Musial, S. Butterfield & B. McNiff (2007). Improving Wind Turbine Gearbox Reliability. Presented at the 2007 European Wind Energy Conference, paper preprint, NREL/CP-500-41548: http://www.nrel.gov/docs/fy07osti/41548.pdf
• Clipper Windpower Plc (2006). Liberty.
Determining Stresses on Life-Limited Components
A TorqueTrak 10K user in a Gulf Coast refinery was having issues with their compressor train. The compressor train uses a synchronous motor drive in a hard start application. In that application, torque pulses occur from 120 Hz to 0 Hz during the transient start-up. When accelerating up to synchronous speed the system passed through torsional resonances. A resonant condition like this creates stress in machinery components that can exceed their endurance limits for fatigue.
The customer found it necessary to analyze these stresses using finite element computer modeling. They then used that information to determine a safe number of system starts. Often in this arrangement, some components in the machinery train are life-limited. By temporarily installing the TorqueTrak 10K with a Micro-Measurements strain gage, the user was able to accurately determine the torques and stresses of the life-limited components. This validated the computer model and allowed the customer to operate the system without concern for further damage.
The TorqueTrak 10K saved the client time and money by avoiding excessive system repairs and the cost of replacing components prematurely.
Torsional Analysis Resolves Pump Motor Failure
A six-stage horizontal centrifugal pipeline shipping pump driven by a 10,000 BHP variable frequency electric motor failed after only four years of operation. Inspection of the failed unit revealed that the rotor bars were badly deformed with points too close to the stator windings. Two identical pumps were inspected and the same problem was detected, though not as severe.
DYNA, a vibration analysis consultant, was called in to investigate the three systems. Utilizing TorqueTrak instrumentation and Micro-Measurements strain gages, test data was collected over the full range of shaft speeds from dead stop on up to the maximum operating speed of 4,100 rpm. Two speeds were found to produce specific torsional vibration amplitudes, indicating a resonance condition, on each of the three pumps. The first (at 720 rpm) was the typical Slow Roll speed. Maximum dynamic torque values as much as 30% of the supplied torque were measured at this speed. The second was at 3,375 rpm, which was within the normal operating range, with peak loads as great as 10% of the supplied torque detected. For an electric motor, the maximum allowable dynamic torque is 1% of the supplied torque. At these shaft speeds, the 6th motor harmonic was exciting resonance in the system and causing high lateral vibration leading to premature failure.
As a result of the analysis, the suggested solutions were to shift the Slow Roll speed up or down 10% and to add inertia (a weighted disk) close to the coupling to move the natural frequency node below the normal operating range. Once implemented, the vibration was eliminated and the reliability of the pumps restored.
TT10K Used to Identify Damage Cause of Coupling Failure
Weeks after commissioning, a compressor unit tripped on high motor vibration. Upon inspection, cracks were found in the center piece of the coupling indicating a possible torsional vibration problem.
The unit consisted of a 3150 HP induction motor operating at 894 RPM, shim pack coupling, flywheel, and 4-throw reciprocating compressor. Full load torque (FLT) of the motor was 222,000 in-lb. After the coupling was repaired, a Binsfeld TorqueTrak TT10K system and a Micro-Measurements strain gage were installed on the motor shaft to measure both transmitted (average) torque and dynamic (alternating) torque.
Peak torque of more than 450% of FLT was initially found with the compressor loaded, which is considered excessive even for reciprocating machinery. However, the signal appeared clipped so the unit was shut down to adjust the transmitter. It is important to check the time wave forms for flat spots, spikes, drop – outs, etc. to ensure good data collection.
Binsfeld includes a convenient remote control that allows easy changing of settings such as channel and gain. Without any soldering of pads, the remote was used to quickly switch the gain from 4000 to 2000. The unit was re-started and the maximum torque was actually 630% of FLT (1,400,000 / 222,000= 6.3).
One engineer questioned the calibration since the torque readings were extremely high. Further comparison with other measurements such as motor current and cylinder pressures verified correct horsepower and that the Binsfeld system was accurate. In addition, the remote had been used to perform built-in shunt calibration during installation of the TT10K to check for proper scale factor.
The high torque exceeded the coupling manufacturer’s allowable limits and caused the failure. The first torsional natural frequency (TNF) was coincident with 5× running speed, which greatly amplified the dynamic torque (AF ˜ 80). For a reliable system, the TNF should have a separation margin (SM) from significant compressor harmonics. API recommends a SM of 10% if possible.
The compressor manufacturer offers “detuners” or internal flywheels that can be bolted onto the crankshaft. This compressor frame can accommodate three detuners, which were promptly ordered from the factory and express shipped to the site. Within a few days the modified compressor unit was re-tested. Strain gage measurements confirmed that this additional inertia lowered the first TNF from 75 Hz to 71 Hz (now 5% below 5× running speed) thus reducing the torque amplitude at that harmonic. The torque levels are now considered acceptable.
By Troy Feese, P.E. Engineering Dynamics Incorporated – San Antonio, Texas, USA http://www.engdyn.com/
Methane Booster Torque and Temperature
Ariel Corporation was working on an issue with Rotor Bearing Technology & Software, Inc. (RBTS) for a company in Australia. Since its start up, the customer had experienced multiple elastomeric element failures in the drive coupling on their large coal bed methane booster compressor at loads and speeds in the design operating range. This compressor unit is driven by a natural gas engine.
The analytical torsional model initially predicted the first mode torsional natural frequency (TNF) to be below 800 RPMs (720 RPM at 30°C and 620 at 100° element temperature at rated engine torque).
Ariel’s Tom Stephens performed site testing with two TorqueTrak instruments with Micro-Measurements strain gages simultaneously: one for coupling dynamic torque, and one for coupling element temperature. Because these elements are part of the rotating coupling assembly, Ariel decided to use telemetry to transmit the signal from their internal temperature sensor. The measurement data indicated the coupling was acting much stiffer than originally modeled with the fundamental twist critical speeds between 800 – 850 RPM. Operating at, or even near, the critical speed was causing the coupling’s elastomeric elements to heat up. The drive train’s fundamental twist mode of vibration was being excited by the inherent unsteady torque demand from the compressor which resulted in damaging levels of torsional vibration in the drive coupling.
The plot shows the coupling element heat generation under different vibratory torque levels – a value below zero indicates that the coupling is cooling down and above zero indicates that it is heating up. Referring to this chart, to prevent the elastomeric elements from overheating, one can see that the vibratory torque level must remain below about 11,000 ft-lbs P-P.
Armed with this data, a slight modification was made to the setup of the coupling assembly which resulted in lowering the drive train’s fundamental twist frequency and ultimately improved compressor reliability. Binsfeld’s TorqueTrak products provided the required telemetry solution to facilitate the simultaneous monitoring both torque and temperature on a rotating coupling assembly which were essential to enabling Ariel and RBTS to fully understand the problem and arrive at a solution.
BINSFELD ENGINEERING INC.
Binsfeld's Torque Measurement Systems measure true mechanical torque and power on rotating shafts. We also offer consultation, strain gaging and installation services.
Binsfeld's Rotary Temperature Transmitter Systems provide accurate and reliable temperature control on heated godets and calendars. We also offer design and OEM services.
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