Shafts vibration

Note In higher speed ranges and for HT motors, Ihese levels of shaft vibration are generally of the same order or slightly belter than prescribed in lEC 60034-14. corresponding to Table 11,3. 

Auxiliary bearing and shaft vibration probe length (given by manufacturer)... 

The maximum permissible vibration, in mils (0.001 in.), during shop test at rated speed shall be equal to the square root of 20,000 divided by the sum of rated speed plus meeh-anieal and eleetrieal runout for the overhung rotor design. Only the aetual total measured runout may be subtraeted from the unfiltered peak-to-peak amplitude measured during testing to attain the shaft vibration. The meehanieal-plus-eleetrieal runout subtraeted from the unfiltered peak-to-peak amplitude shall not exeeed 0.5 mils regardless of total runout. 

High-speed eouplings must be balaneed very earefully and, with a low overhung moment, the effeet of eoupling overhung moment is felt not only in maehine bearing load but in shaft vibration. 

To analyze a turbine, it is neeessary to measure pressures and temperatures aeross the turbine, shaft vibration, and the temperature and pressure of the lubrieation system. Table 19-7 shows the effeet various parameters have on important funetions of the turbines. Analysis of these parameters will aid in the predietion of ... 

Figure 8-33. Three methods for measuring shaft vibration. (Courtesy of Bently Nevadelf...

The vibration characteristics, determined by use of the instrumentation, will serve as the basis for acceptance or rejection of the machine. API standards generally require that the equipment be operated at speed increments of approximately 10% from zero to the maximum continuous speed and run at the maximum continuous speed until bearings, lube-oil temperatures, and shaft vibrations have stabilized. Next, the speed should be increased to trip speed and the equipment run for a minimum of 15 minutes. Finally, the speed should be reduced to the maximum continuous speed and the equipment should be run for four hours. API does not require that the four hours be uninterrupted however, it is generally interpreted that way. The interpretation is one of the many test criteria to be discussed. It would seem that a break in the test at the midpoint is not the same as having it cut short five minutes from the end because the vendor s boiler took an upset that was not related to the compressor test. The ibration during the shop test is normally specified as the API limit of 1.0 mils peak to peak, or the value from Equation 10.1, unfiltcred. whichever is lower. 

Shaft vibration measurement methtxls, 350 Shaking forces reciprocating, 368, 378 rotary, 382... 

Most generators have relatively soft support structures. Therefore, they require shaft vibration monitoring measurement points in addition to standard casing measurement points. This requires the addition of permanently mounted proximity, or displacement, transducers that can measure actual shaft movement. 

The units for shaft vibration measurement shall be peak-to-peak displaeement in pm (mils). 

Pumps furnished with proximity probes shall meet both bearing housing and shaft vibration limits. 

Selection of agitator drive and speed reducer Mechanical assessment of shaft. Vibrations Mass transfer at bubble/liquid, and liquid/solid... 

Instead of blindly looking at the shaft vibration and comparing it to a fixed threshold, we propose to identify the parameters influencing this vibration. Three significant parameters were identified oil temperature, speed, and load. Using historical data of the machine to be monitored or, if not available, of other machines of the same type, we can correlate this vibration with the three parameters. This results in a regression formula that can be coded in the rule engine to be applied on-line. This correlation study will be the focus of a future paper. 

During periods of normal operation several parameters are monitored, including turbine shell temperature and pressure, exhaust hood temperature, bearing oil temperature and pressure, condenser vacuum, shaft vibration, hydraulic oil pressure, and generator gas and winding temperatures. 

The pump failure can be associated with wear that can cause unbalancing and consequently mains shaft vibration. The use of accelerometers as vibration transducers allows the use of condition-based monitoring of the pump. Also, ultrasound analysis can be applied for detection of cavitation at the pump. 

Seal failures are the most common type of failure associated with rotating equipment. Since seals are a barrier between the process and the atmosphere, such failures are often likely to lead to environmental problems, and potentially a safety problem depending on factors such as the flammabUity/toxicity of the process fluid, the size of the leak, and its proximity to personnel or ignition sources. Seal failures can be caused by problems with the bearings, couplings, and shaft vibration. 

Shaft vibration detecting equipment continuously monitors the actual dynamic conditions of the machine. 

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