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ISO TC 108/SC 1
ISO/DIS 20806
ISO TC 108/SC 1/WG 15 Secretariat: ANSI
Mechanical vibration In-situ balancing of rotors Guidance, safeguards and reporting
lment introductif lment central lment complmentaire
Document type: International Standard Document subtype: Document stage: (40) Enquiry Document language: E G:\WPFILES\TC108\SC1\20806\ISO_DIS_20806_(E).doc STD Version 2.1
Foreword .............................................................................................................................................................v Introduction........................................................................................................................................................vi 1 2 3 4 4.1 4.2 5 6 6.1 6.2 6.3 6.4 6.5 7 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 8 9 10 10.1 10.2 10.2.1 10.2.2 10.2.3 10.3 10.4 10.4.1 10.4.2 10.4.3 10.5 10.5.1 10.5.2 10.5.3 10.5.4 Scope ......................................................................................................................................................7 Normative references............................................................................................................................7 Terms and definitions ...........................................................................................................................7 In-situ balancing ....................................................................................................................................7 General ...................................................................................................................................................7 Reasons for in-situ balancing ..............................................................................................................8 Criteria for in-situ balancing ................................................................................................................8 Safeguards .............................................................................................................................................9 General ...................................................................................................................................................9 Safety of personnel while operating close to a rotating shaft..........................................................9 The special operating envelope for in-situ balancing .......................................................................9 Integrity and design of the correction masses and their attachments............................................9 Machinery specific safety implications.............................................................................................10 Measurements .....................................................................................................................................10 Vibration measurement equipment ...................................................................................................10 Measurement errors ............................................................................................................................10 Phase reference signals .....................................................................................................................11 General .................................................................................................................................................11 Information required for reproducible phase reference data .........................................................11 Phase data when using trial masses as the phase reference ........................................................12 Operational conditions .......................................................................................................................13 Acceptance criteria .............................................................................................................................13 Reporting..............................................................................................................................................13 General .................................................................................................................................................13 Introduction..........................................................................................................................................13 Background..........................................................................................................................................13 Objective ..............................................................................................................................................14 Machine details....................................................................................................................................14 Vibration measurement equipment ...................................................................................................14 Results..................................................................................................................................................14 Correction masses ..............................................................................................................................14 Tabular data : Vibration results and correction mass configurations...........................................15 Graphical data......................................................................................................................................15 Text information ..................................................................................................................................15 General .................................................................................................................................................15 Discussion ...........................................................................................................................................15 Conclusion ...........................................................................................................................................16 Recommendations ..............................................................................................................................16
Annex A (informative) Precautions and safeguards for specific machine types during in-situ balancing..............................................................................................................................................18 Annex B (informative) Sample in-situ balancing report for a boiler fan <1MW ..........................................19 B.1 Background..........................................................................................................................................20 B.2 Objective ..............................................................................................................................................20 B.3 Instrumentation ...................................................................................................................................20
B.3.1 B.3.2 B.3.3 B.3.4
Vibration Transducers........................................................................................................................ 20 Phase Reference Transducers .......................................................................................................... 20 Analysis system.................................................................................................................................. 20 Results ................................................................................................................................................. 21
Annex C (informative) Sample balancing report for a large, >40 MW, turbine generator......................... 24 C.1 Background ......................................................................................................................................... 25 C.2 Objective.............................................................................................................................................. 25 C.3 Machine details ................................................................................................................................... 25 C.4 Instrumentation................................................................................................................................... 25 C.5 Results ................................................................................................................................................. 26 C.5.1 Correction masses ............................................................................................................................. 26 C.5.2 Tabular data......................................................................................................................................... 27 C.5.3 Vector changes ................................................................................................................................... 27 C.6 Vibration Signatures........................................................................................................................... 27 C.7 Discussion........................................................................................................................................... 29 Bibliography ..................................................................................................................................................... 30
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 20806 was prepared by Technical Committee ISO/TC 108, Mechanical vibration and shock, Subcommittee SC 1, Balancing, including balancing machines.
Balancing is the process by which the mass distribution of a rotor is checked and, if necessary, adjusted to ensure that the residual unbalance or the vibrations of the journals/bearing supports and/or forces at the bearings are within specified limits. Many rotors are balanced in specially designed, balancing facilities prior to installation into their bearings at site. However, if remedial work is carried out locally or a balancing machine is not available, it is becoming increasingly common to balance the rotor in-situ. In-situ balancing is the process of balancing a rotor in its own bearings and support structure, rather than in a balancing machine. (This is the same definition as field balancing in ISO 1925:2001, but in-situ balancing is easier to understand and will be used in the future.) A general guide to the ISO standards associated with mechanical balancing of rotors is given in ISO 19499. Rotors in a constant (rigid) state are covered by ISO 1940-1 and rotors in a shaft elastic (flexible) state are covered by ISO 11342.
This International Standard gives guidance and safeguards that shall be adopted when balancing rotors installed in their own bearings on site. It addresses the conditions under which it is appropriate to undertake in-situ balancing, the instrumentation required, the safety implications and the requirements for reporting and maintaining records. The standard may be used as a basis for a contract to undertake in-situ balancing. This International standard does not provide guidance on the methods used to calculate the correction masses from measured vibration data.
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including amendments) applies. ISO 1925, Mechanical Vibration Balancing Vocabulary ISO 2041, Vibration and shock Vocabulary ISO 2954, Mechanical vibration of rotating and reciprocating machinery - Requirements for instruments for measuring vibration severity. ISO 7919 (All parts), Mechanical vibration of non-reciprocating machines Measurements on rotating shafts and evaluation criteria. ISO 10816, (All parts) Mechanical vibration Evaluation of machine vibration by measurements on non-rotating parts. IS0 10817-1, Rotating shaft vibration measuring systems Part 1: Relative and absolute sensing of radial vibration.
For the purpose of this International Standard, the terms and definitions given in ISO 2041 and ISO 1925 apply.
In-situ balancing is the process of balancing a rotor in its own bearings and support structure, rather than in a balancing machine. (This is the same definition as field balancing in ISO 1925:2001, but in-situ balancing is easier to understand and will be used in the future.) For in-situ balancing, correction masses are added to the rotor at a limited number of conveniently engineered and accessible locations along the rotor. By so doing the magnitude of shaft and or pedestal vibrations and/or
unbalance will be reduced to within acceptable values so that the machine can operate safely throughout its whole operating envelope. In certain cases, machines that are very sensitive to unbalance may not be successfully balanced over the complete operating envelope. This usually occurs when a machine is operating at a speed close to a lightly damped system mode, (see ISO 10814), and has load dependent unbalance. Unlike balancing in a specially designed balancing machine, in-situ balancing has the advantage that the rotor is installed in its working environment. Therefore there is no compromise with regard to the dynamic properties of its bearings and support structure, nor from the influence of other elements in the complete rotor train. However, it has the large disadvantage of restricted access and the need to operate the total machine. Restricted access may limit the planes at which correction masses can be added and using the total machine has the commercial penalties of both down time and running costs. Where gross imbalance exists it may not be possible to balance a rotor in-situ due to limited access to balance planes and the size of correction masses available. Most sites have limited instrumentation and data processing capabilities, when compared to a balancing facility and additional instrumentation is often required to undertake in-situ balancing. In addition, the potential safety implications of running a rotor with correction masses need to be taken into account.
Reasons for in-situ balancing
Although individual rotors can be correctly balanced, as appropriate, in a high or low speed balancing machine, insitu balancing may be required when the rotors are coupled into the complete rotor train. This could be due to a range of differences between the real machine and the isolated environment in the balancing machine, including: A difference in the rotor supports dynamic characteristics between the balancing facility and the installed machine. Assembly errors, which occur during the installation of the machine in-situ. Rotor systems that cannot be balanced prior to assembly. A changing unbalance state of the rotor under full functional operating conditions. Balancing may also be required to compensate for in-service changes to the rotor, including: Wear Loss of components, such as rotor blade erosion shields Repair work, where components could be changed or replaced Movement of components on the rotor train causing unbalance, such as couplings, gas turbine discs, and generator end rings Additionally in-situ balancing may be necessary due to a range of economic and technical reasons, including: The investment in a balancing machine cannot be justified A suitable balancing machine is not available in the correct location or at the required time It is not economic to dismantle the machine and transport the rotor(s) to a suitable balancing facility
Criteria for in-situ balancing
Machines under normal operation and/or during speed variations, following remedial work, or after commissioning may have unacceptable magnitudes of vibration when compared with normal practice, contractual requirements, or standards such as ISO 10816 and ISO 7919. In many cases it may be possible to bring the machine to within acceptable vibration magnitude by in-situ balancing.
Prior to in-situ balancing a feasibility study shall be carried out to assess if the available correction planes are suitable to influence the vibration behaviour being observed, since limited access to correction planes and measurement points on the fully built up machine may make in-situ balancing impractical. Where possible, experience from previous in-situ balancing should be used. Sometimes modal analysis may be required. High vibrations shall always be corrected at their source and in-situ balancing shall only be attempted in the following circumstances: The reasons for the high vibrations are understood or, after analysis of the vibration behaviour, it is judged that balancing is a safe and practical approach. Under the required normal operating conditions the vibration vector shall be steady and repeatable prior to in-situ balancing. The addition of corrections masses will only affect the once per revolution component of vibration and therefore in-situ balancing shall only be considered if this is a significant component of the overall vibration magnitude. In special circumstances, where the once per revolution vibration component changes during normal operation of the machine, such as thermally induced bends in generator rotors, it may be possible to optimise the vibration magnitude across the operating envelope by adding correction masses. Here, the vibration magnitude at full speed no load may be compromised to obtain an acceptable vibration magnitude at full load. Again this shall only be attempted if the reasons for the unbalance are fully understood.
NOTE 1 When systems are operating in a non-linear mode correction masses can affect other shaft components, including both sub and high shaft speed harmonics. NOTE 2 The once per revolution component of vibration may not originate from unbalance but be generated from system forces such as those seen in hydraulic pumps and electric motors. Many defects, such as shaft alignment errors and tilting bearings, can also contribute to the once per revolution component of vibration. Such effects should not normally be corrected by balancing, since balancing may be effective at only a single speed and could mask a real system fault.
In-situ balancing can place the total machine and staff at risk. Therefore, it shall only be undertaken by a skilled team, including both customer and supplier, who understand the consequences of adding trial and correction masses and have experience of operating the machine.
Safety of personnel while operating close to a rotating shaft
While undertaking in-situ balancing the machine may be operated under special conditions, allowing access to rotating components to add trial and final correction masses. Strict safety procedures shall be in place to ensure that the machine cannot be rotated while personnel have access to the shaft and no temporary equipment can become entwined when the shaft is rotated.
The special operating envelope for in-situ balancing
Machines may be quickly run up and run down many times during the in-situ balancing exercise, which may be outside a machine's normal operating envelope. It shall be established that this will not be detrimental to the integrity or the life of the total machine.
Integrity and design of the correction masses and their attachments
When trial and correction masses are added it shall be confirmed that they are securely attached and their mountings are capable of carrying the required loads. The correction masses shall not interfere with normal
operation, such as coming in contact with stationary components due to shaft expansion. The correction masses should be fitted in accordance with the manufacturers instructions, if available. Correction masses are often attached with bolts or by welding. It shall be ensured that the bolt holes or the welding process do not compromise the integrity of the rotor component to which the correction masses are attached or the function of the component, such as cooling. Further, correction masses shall be compatible with their operating environment, such as heat and chemical atmosphere.
Machinery specific safety implications
General safety requirements associated with in-situ balancing are discussed above, but additional considerations for specific machine types are given in Annex A.
Basic procedures for the evaluation of vibration by means of measurements made directly on the rotating shaft shall comply with ISO 7919-1 and the measurement system shall comply with ISO 10817-1. Measurement procedures for transducers mounted on the pedestal shall comply with ISO 10186-1 and the measurement system shall comply with ISO 2954. Either system shall have sufficient frequency range to capture data for the full speed range over which the machine is to be balanced. The transducers shall have the necessary sensitivity and be located at the appropriate positions to measure the effects of the correction masses. In general, on flexible support structures pedestal measurements give the best results and on rigid supports, shaft relative transducers will be more responsive. However, when using the signals from eddy-current probes (as often permanently installed in turbo machinery for vibration monitoring purposes) for non-contact shaft vibration measurements, the once-perrevolution signals of the unbalance measurement may be superimposed by erroneous but speed-frequent signal components. These resulting from mechanical and/or electrical runout of the machine shaft. If available, shaft absolute measurement can be used, which provides a shaft position independent of the pedestal movement. Standards ISO 7919 and ISO 10816 are concerned with the overall vibration magnitude for acceptance criteria. For balancing the vibration measurement equipment shall have the additional facility to extract the once per revolution component of vibration, giving both amplitude and phase. Where in-situ balancing is being undertaken to reduce the vibration magnitude at the operating speed and while passing through the system resonances, during run up and run down, the measurement equipment shall be sufficiently accurate in both magnitude and phase to cover the full speed range under consideration. Vibration shall be measured at selected locations where it is necessary to reduce its magnitude. However, balancing may improve the vibration magnitude at other locations or directions at the expense of another. Therefore, it is recommended to have additional transducers on adjacent rotors or bearings. For monitoring, vibration may be only measured in the vertical direction on the pedestal, but when in-situ balancing, it would be advisable to measure both vertical and horizontal vibration. Where installed transducers are used it is advisable to check their calibration, in both magnitude and phase, immediately prior to balancing. Permanently installed shaft relative transducers are not normally checked for calibration but a phase and shaft run out check would be advisable. In some cases, it may be useful to measure the full orbit of vibration and in this instance it is necessary to have pairs of transducers at selected axial measurement locations along the shaft. Strictly, it is only necessary to have two non-parallel transducers to describe the orbit, however orthogonal pairs are usually used.
Any measurement is subject to error, which is the difference between the true and the measured values. The difference is called the error of measurement and, in balancing, this is caused by a combination of systematic, randomly variable and scalar errors. Systematic errors are those when both magnitude and phase of the balance
error can be evaluated by either calculation or measurement. Random errors are those when both the magnitude and phase of the balance can vary unpredictably and scalar errors occur when the magnitude of the balance can be evaluated or estimated but the angle is undefined. ISO 1940-2 gives examples of typical errors that can occur in the field of balancing and provides procedures for their determination. Some of the examples presented are for the balancing facility, but many are applicable to insitu balancing. The limit for these errors shall be matched to the acceptance criteria of the in-situ balancing, as agreed between the supplier and the customer (see clause 9).
Phase reference signals
A phase reference mark, such as a keyway or reflective tape, is usually placed on the shaft or any synchronous part and is detected by a transducer mounted on a non-rotating component, such as a bearing pedestal. This provides a once per revolution signal from which the phase can be measured. Sometimes the reference mark is permanently installed. The reference mark, such as a keyway or markings on the shaft, shall be clearly documented and, if possible, visible to allow correction masses to be accurately placed. In addition, the direction of shaft rotation shall be established so that phase angles, with or against rotation, can be translated into the appropriate correction mass locations. Measured angles with rotation (phase lead) will require correction masses to be located in the direction of rotation from the leading edge of the phase mark. Angles measured against rotation (phase lag) will require the correction mass to be located against the direction of rotation from the leading edge of the phase mark. Alternative phase definitions can be adopted but whatever system is used it shall be clearly defined and it is good practice to ensure that the phase angle used for the location of the correction mass is consistent with the phase angle of the once per revolution vibration. 7.3.2 Information required for reproducible phase reference data
The position of the shaft phase reference shall be consistently defined to provide accurate records so that previous and future in-situ balancing data can be compared (see clause 10). The pulse generated by the shaft mark shall be sharp so that different trigger levels will not lead to inaccurate phase measurements. The sinusoidal type signal, Figure 1, can give a trigger time dependent on the level of the trigger setting but the sharp pulse, Figure 2, will give a trigger time independent of the trigger voltage setting. Triggering shall be from the leading edge of the pulse, for either negative or positive going pulses, (either negative or positive slope). Triggering on the trailing edge could lead to significant phase errors, since the pulse width may not reflect the width of the phase mark and may depend on the pulse signal conditioning.
Time of trigger level 1 Time of trigger level 2 Trigger level 1
Trigger level 2
Figure 1 Bad phase reference signal where a change in trigger level will cause a change in the time of zero phase
Same time for trigger levels 1 and 2 Trigger level 1
Tachometer signals Time
Figure 2 Good phase reference signal that will give a time for zero phase independent of trigger level
Phase data when using trial masses as the phase reference
If the in-situ balancing process adopted uses a trial correction mass or set as the initial run and all subsequent runs are compared with this, it may not be necessary to have a detailed knowledge of the phase reference signal, as described in section 7.3.2. All correction mass locations will be relative to the position of the initial trial mass(es) and errors introduced by the measurement system will have less significance. However, using the trial mass(es) phase reference approach, the same equipment and trigger settings shall be used throughout the whole in-situ balancing exercise and the phase data collected may have no significance relative to previous or future data. In addition, the position of the initial trial correction mass(es) may increase the vibration magnitude. This could be unacceptable for a machine that is already operating at a high vibration magnitude.
Vibration data for the balancing runs shall only be collected under sufficiently steady and repeatable operating conditions, which may influence the vibration, such as, fluid flow, electrical current, and pressure. This may require pre-balance tests to determine what are the effects of the operating conditions. For example machines may have thermal transients during initial start-up and it may be necessary to run for sufficient time to reach normal operating conditions prior to taking the vibration values. Additional testing may also be required, when a non-linear behaviour is suspected. Under this condition the first shaft order vibration vector change will not be linearly related to the position and location of the correction mass. When vibration data is collected under transient speed conditions, the rate of change (increasing or decreasing speed) may be important.
Normally the reason for balancing is to reduce the vibration magnitude(s) to acceptable values for long term operation. For most machines, the overall vibration magnitude(s) shall either be based on normal practice or the appropriate part of ISO 10816 and ISO 7919 for pedestals and shafts respectively. Where the level of imbalance is important it may be necessary to reduce the level of unbalance to within permissible limits, ISO 1940-1. However, in some cases balancing may be carried out to enable continued running until a planned outage or optimised for a specific operating condition. In such circumstances other acceptance criteria may be used, which shall be agreed between the supplier and the customer.
The level of reporting will depend on the type of machine being balanced. This section outlines information that shall be reported and Table 1 provides broad guidance of normally acceptable levels of reporting related to the type of machine being balanced. Annexes B and C show sample balancing reports for a small fan and a large turbine generator respectively. Balancing shall be accurately reported to maintain records of correction masses added to the rotors. This is especially important when rotors are removed for remedial work, so that correction masses added to correct for defects in the rotor train could be distinguished from those added for individual rotors. Good balancing records are also required to assist in understanding the machines behaviour, enabling its response to be predicted in relation to correction mass additions. This simplifies further balancing procedures and aids the identification of fault locations, when problems occur. Even on smaller, low cost machines, records and patterns of correction mass additions shall be maintained to identify generic or rogue plant problems. Before in-situ balancing is undertaken, the need to add correction masses shall be understood. If possible the report should include the reasons for the unbalance and the information used to reach this conclusion.
10.2.1 Background Any relevant machine history shall be highlighted, with particular consideration being given to the recent operating regime and maintenance work.
10.2.2 Objective Reports for all classes of machine shall clearly outline the objective for the in-situ balancing exercise. Normally the reason for balancing will be to reduce the vibration levels to acceptable levels but in special circumstances it may be necessary to reduce the unbalance to permissible limits. 10.2.3 Machine details In some cases a schematic diagram of the total machine being balanced should be provided, indicating all the rotors and the location of the thrust and support bearings. All vibration transducer locations and directions shall be clearly shown, plus the position and orientation of the phase reference mark. The direction of shaft rotation shall also be included with respect to the viewing direction along the shaft. Where more complex features are incorporated in the machine design that effect the balance condition, these shall be highlighted.
10.3 Vibration measurement equipment
Details of all equipment used for the vibration measurements shall be recorded. Transducers used shall be clearly documented, showing their type, serial numbers, sensitivities, locations and orientations.
All data provided shall be presented with its measurement units, for example: Vibration displacement m pk-pk m 0-pk mil pk-pk mil 0-pk Vibration velocity mm/s rms mil/s rms Correction mass g lb Correction mass radius mm in NOTE Vibration units highlighted are those adopted by ISO 7919 and ISO 10816 10.4.1 Correction masses The complete configuration of each correction mass shall be presented giving: axial location along the shaft radial location magnitude of the installed correction mass
angle relative to the phase reference position This data can be presented in either a graphical or tabular form, as appropriate, showing any existing masses, where these are present. Mass data for the final configuration shall always be provided, but with complex balancing exercises, where a number of runs took place, it may be appropriate to present the balance mass configurations for each run, subject to agreement between the supplier and the customer.
Note 1 The phase angle convention (lead or lag) for the attachment of the correction masses shall be defined. Note 2 It is recommended to distinguish between the original correction masses already on the rotor and those added during the in-situ balance exercise.
10.4.2 Tabular data : Vibration results and correction mass configurations Vibration measurements for the initial run and at least the final run shall be presented in tabular form. This shall include the overall magnitude of the vibration and its once per revolution amplitude and phase at each measurement location. This shall be provided at the normal operating speed and at any other speed where the vibration is of concern, normally while passing through critical speeds. With complex balancing exercises, where a number of runs are required, it may be appropriate to present all the vibration data together with correction mass configurations for each run, subject to agreement between the supplier and the customer. The phase angle convention (lead or lag) for the attachment of the correction masses shall be defined. 10.4.3 Graphical data 10.4.3.1 Vibration vector changes
Polar plots, showing the vector changes from the initial to the final balancing run of the once per revolution vibration, in amplitude and phase may complement the tabular data for each relevant measurement position. Where multiple balancing runs are used, the progressive vector changes may be appropriate, subject to agreement between the supplier and the customer. For constant speed machines the vibration vector changes (from the initial to final balance runs) at the normal operating speed shall be shown. However, if other speeds are important, such as passing through shaft critical speeds, it may be necessary to include these vector changes as well. Influence coefficients may be required in special circumstances, subject to agreement between the supplier and the customer. 10.4.3.2 Vibration signatures
Wherever possible, pre and post balancing data showing the once per revolution vibration, in amplitude and phase, should be included for relevant measurement locations over the full operating envelope, run up, loading, steady state and run down. In addition, it would normally be necessary to present the overall vibration magnitude to confirm that the reduction in the once per revolution amplitude has been sufficient to ensure that the overall acceptance criteria have been satisfied.
10.5 Text information
10.5.1 General The quantity of descriptive text required for the reporting should be minimal, but sufficient to explain the presented data. 10.5.2 Discussion A discussion shall be included to explain and summarise the steps taken to add the mass corrections and highlight significant events that took place during the balancing runs.
10.5.3 Conclusion Significant results shall be stated and the post balancing results compared to the appropriate acceptance criteria. 10.5.4 Recommendations Any recommended actions resulting from the in-situ balancing shall be highlighted.
Table 1 In-situ balancing reporting. This table provides broad guidance of normally acceptable levels of reporting related to the type of machine being balanced. Type of machine Size Background Machine details Instrumentation details Results Correction mass(es) Section 10.2.1 10.2.3 10.3 10.4 1 Tabular 10.4.2 Graphical Vectors 10.4.3.1 Boiler Fans <1MW >1MW Main boiler feed pumps <1MW >1MW Electric motors <1MW >1MW Large gas turbines <40MW >40MW Large steam turbines <40MW >40MW Electrical generators <10MW >10MW Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes(1) Yes(1) Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes YesYes Yes Yes Yes Yes Yes Signatures 10.4.3.2 -
NOTE 1 If a supplementary installation is used to perform the balance, the instrumentation details shall be reported.
Annex A (informative) Precautions and safeguards for specific machine types during in-situ balancing
It is not possible to define all safety precautions associated with operating rotating machines for in-situ balancing, however, some key considerations are highlighted here for specific machine types. Machine type
Steam and turbines gas
Before a turbine shaft is stopped to add correction masses or establish phase signal references, it shall be confirmed that the correct procedures are undertaken to prevent bending of the shaft. This will normally involve barring for a period of time to reduce the shaft temperature. The rotor life may be related to the number of machine starts and this needs to be considered in relation to the starts required for the in-situ balancing runs.
Some electric motors have restrictions on the number of starts per hour and this shall not be exceeded. Electric motors may run from zero to full speed with no intermediate control. Trial masses shall be of a size that will not cause damage to the machine, even if placed in the wrong position.
Main boiler pumps
Some pumps need to be full of fluid for their safe operation and in-situ balancing runs will not generally be an exception. During the in-situ balancing runs the flow induced by the fan shall be correctly accommodated. For example dampers may need to be shut and this may place the fan under stall conditions. The fans may be pumping hot or hazardous fluids and personnel shall not be allowed to enter the fan to add correction masses until conditions are safe.
Large induced and forced draft fans
Large hydrogen cooled electrical generators driven by steam or gas turbines
The considerations related to the turbines apply also to the generators. For easy access to the in-situ balancing planes, it may be advisable to run the generator in air instead of hydrogen; however, most generators have restrictions on the maximum running speed and duration of the in air runs, even at no-voltage and no-load. It shall be established that the seal oil system would provide adequate lubrication of the gland seals when the generator is running in air. For easy access to the in-situ balancing planes, it may be necessary to dismantle some of the internal baffling of the cooling circuit; consideration shall be given to the effect of such modifications on the generator cooling and cleanness
Annex B (informative) Sample in-situ balancing report for a boiler fan <1MW
Ref: XXXX Date: To: Mr J Smith Station Manager XXXXX Power Station Prepared by: Mr D Brown XXXXX Balancing Services Ltd Approved by: Mr S Daves Turbine Generator Group Manager
Subject: XXXXX Power Station Unit 2 2A PA (Primary Air) boiler fan In-situ Balance, 11 January 2002 Conclusion The in-situ balancing of unit 2A PA boiler fan was successful in reducing the vibration magnitude to within Zone B of the ISO 10816.part 3 group 3, rigid foundations
Copies to: Mr R McWhannel XXXX Power Station Task Number Number of pages Number of tables Number of figures 1 0
Unit 2 PA fan, 2A, has had a history of blade tip erosion, leading to debris accumulating inside the blade section. The fan has now been cleaned and the blade tips repaired and balancing is required to correct for unbalance introduced by this work.
B.2 Objective
To reduce the vibration levels, as measured on the pedestals, to levels that are suitable for continuos long term operation.
B.3 Instrumentation
Portable instrumentation was used to undertake this balancing, with a single transducer being used for all locations.
B.3.1 Vibration Transducers
Manufacturer Type Serial Number Sensitivity Location (If applicable) Orientation
B.3.2 Phase Reference Transducers
Manufacturer Type Serial Number Location Orientation
B.3.3 Analysis system
Manufacturer Type Serial Number Date of last calibration
B.3.4 Results
Non drive end pedestal Vertical Horizontal First shaft order mm/s rms Phase lag degrees 8 343 7 Overall mm/s rms First shaft order mm/s rms Phase lag degrees 264 236 265
Drive end pedestal Vertical Overall mm/s rms First shaft order mm/s rms Phase lag degrees Horizontal Overall mm/s rms First shaft order mm/s rms Phase lag degrees 264 235 262
Correction mass Mass at centre span 0.7 m radius
Overall mm/s rms
phase lag degrees
11/01/02 11/01/02 11/02/02
20:05 21:50 23:30
13.5 9.3 2.4
13.3 9.2 2.3
8.9 7.2 1.8
8.7 7.0 1.6
12.9 9.1 1.7
12.6 9.0 1.6
9 340 11
8.1 6.3 1.0
7.9 6.1 0.9
Table B1Vibration data from the balancing of 2A PA fan The phase reference signal and horizontal vibration transducers were measuring in the same direction.
290 300 310 320 330 340 Maximum radius 15 mm/s rms
160 150 140 130 120 110 100 90 270 80 70 60 50 40 30
20 Angle phase lag
Non drive end Vertical Non drive end Horizontal
Drive end Vertical Drive end Horizontal
Figure B1 Drive end and non-drive pedestal vibrations (Not generally necessary for small fans of this size.)
Annex C (informative) Sample balancing report for a large, >40 MW, turbine generator
Subject: XXXXX Power Station Unit 2 Turbine generator In-situ Balancing following return to service, 11 January 2002 Conclusion The in-situ balancing was successfully carried out reducing the vibration magnitude on the LP pedestal bearings to within Zone B of ISO 10816. Part 2.
Copies to: Mr R McWhannel XXXX Power Station Task Number Number of pages Number of tables Number of figures
Unit 2 turbine generator at XXXX Power Station returned from a major overhaul. During the overhaul the LP (Low pressure) rotors had work carried out on their last stage blades. Although these rotors where low speed balanced, higher than acceptable vibration magnitudes were measured on the bearings supporting the LP rotors. Such behaviour is common on this class of machine and is normally attributed to concentricity errors associated with an unsupported dumbbell shaft joining the two LP rotors. An in-situ balance exercise was requested to correct for the unbalance introduced by this concentricity error.
To reduce the vibration levels, as measured on the pedestals, to levels that are suitable for continuos long term operation at normal operating speed. Vibration levels while passing through system resonances under transient speed conditions shall also remain within acceptable limits.
C.3 Machine details
The 350 MW, 3000 rpm machine comprises of an HP (High pressure turbine), IP (Intermediate pressure turbine) and two LPs (Low pressure turbine) coupled to a hydrogen cooled generator and an exciter. The bearings monitored during the return to service were as follows: Bearing number 4 5 6 7 8 9 Machine position IP rear LP1 forward LP1 rear LP2 forward LP2 rear Generator forward
C.4 Instrumentation
Vibration data from temporary installed velocity transducers was analysed and stored using a portable data collector. This provided both real time and archive facilities, giving the overall magnitude of vibration and the once per revolution amplitude and phase. A permanently installed shaft reference was used, which is installed at the exciter in a horizontal direction on the right hand of the machine, looking from the HP end. The direction of rotation is anti-clockwise looking from the same end. Analyser type: ________Analyser Serial Number: _______ Date of last calibration: ________
Channel 1 2 3 4 5 6 7 8 9 10 11 12
Location Bearing No 4 4 5 5 6 6 7 7 8 8 9 9
Orientation Vertical Horizontal Vertical Horizontal Vertical Horizontal Vertical Horizontal Vertical Horizontal Vertical Horizontal
Horizontal is at the half joint on the right hand side of the machine as viewed from the HP end and the phase reference transducer is this same direction. The vertical position is on the top of the bearing. Phase reference transducer Manufacturer Type Serial Number Location Adjacent to bearing 4 Orientation Horizontal
C.5.1 Correction masses
The final correction mass configuration was 0.6 kg at a 30 mm radius on the bearing 6 end dumbbell coupling and 2.0 kg at a 30 mm radius on the bearing 7 end, both at zero phase relative to the shaft marker. No previous correction masses were found.
Note: Only sample results will be presented for this example, not the complete set as would be expected in the full report.
C.5.2 Tabular data
Date Time Condition Speed Bearing 7 Vertical Overall mm/s rms 11/01/02 12/01/02 20:05 08:50 Initial Final 3000 3000 14.0 3.7 First shaft order mm/s rms 13.7 3.3 phase lag degrees 310 302 Horizontal Overall mm/s rms First shaft order mm/s rms phase lag degrees
C.5.3 Vector changes
Bearing 7 Vertical
Figure C1 Vibration vector change for bearing 7 vertical
C.6 Vibration Signatures
(In some circumstances it may be necessary to show changes in vibration during a full loading cycle, including the run up, raise to full operational load at normal operational speed and the subsequent rundown. Here only the rundown is presented.)
Amplitude / mm/s rms
0.0 0 10 20 30 Frequency / Hz 40 50 60
Figure C2 Vibration amplitude during rundown from bearing 7 vertical
Phase / Degrees
20 Unbalanced Balanced -30
-180 0 10 20 30 Frequency / Hz 40 50 60
Figure C3 Vibration phase during rundown from bearing 7 vertical
C.7 Discussion
The key problem of this machine was the high magnitudes of vibration during run down at around 1200 rpm (20 Hz) and 2880 rpm (48 Hz). The in-situ balancing successfully reduced the magnitude of vibration at both these peaks and at the normal operating speed of 3000 rpm (50 Hz).
ISO 1940-1, Mechanical vibration Balance quality requirements for rotors in a constant (rigid) state Part 1: Specification and verification of balancing tolerances ISO 1940-2, Mechanical vibration - Balance quality requirements of rigid rotors - Part 2 Balance errors ISO 10814 Mechanical vibration - Susceptibility and sensitivity of machines to unbalance ISO 11342, Mechanical vibration Methods and criteria for the mechanical balancing of flexible rotors ISO 19499, Mechanical vibration Balancing and to balancing standards - Introduction
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