ISO 14839-2:2004
(Main)Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 2: Evaluation of vibration
Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 2: Evaluation of vibration
ISO 14839-2:2004 sets out general guidelines for measuring and evaluating rotating machinery equipped with active magnetic bearings (AMBs) with respect to the following two indices: shaft vibratory displacement measured at or close to the AMBs; and working current and voltage measured in magnetic coils or power supply amplifiers. Both indices are measured under nominal operating conditions in house and/or on site. These guidelines are presented in terms of both steady-state running values of these indices and any magnitude changes which may occur in these steady-state operations. ISO 14839-2:2004 is applicable to industrial rotating machines generating or consuming nominal power greater than 15 kW, and is not limited by size or operational rated speed (i.e. comprising turbo-compressors, turbo-pumps, steam turbines, turbo-generators, turbo-fans, electric drives and other rotors supported by AMBs). It establishes the vibration, current and voltage evaluation of the rotating machinery equipped with AMBs, specified by a comparatively large power capacity as described above, excluding small-scale rotors such as turbo-molecular pumps, spindles and flywheels. ISO 14839-2:2004 covers both AMB-equipped rigid rotors and AMB-equipped flexible rotors.
Vibrations mécaniques — Vibrations de machines rotatives équipées de paliers magnétiques actifs — Partie 2: Évaluation des vibrations
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 14839-2
First edition
2004-09-01
Mechanical vibration — Vibration of
rotating machinery equipped with active
magnetic bearings —
Part 2:
Evaluation of vibration
Vibrations mécaniques — Vibrations de machines rotatives équipées de
paliers magnétiques actifs —
Partie 2: Évaluation des vibrations
Reference number
©
ISO 2004
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
©
ii ISO 2004 – All rights reserved
Contents Page
1 Scope . 1
2 Normative references . 1
3 Measurement and evaluation procedures . 1
4 Evaluation criteria . 6
Annex A (informative) Case study on an LP centrifugal compressor equipped with active magnetic
bearings (AMBs) . 8
Annex B (informative) Case study on current evaluation . 14
Annex C (informative) Voltage saturation . 17
Bibliography . 20
©
ISO 2004 – All rights reserved iii
Foreword
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.
ISO14839-2 was prepared by Technical Committee ISO/TC108, Mechanical vibration and shock,
Subcommittee SC 2, Measurement and evaluation of mechanical vibration and shock as applied to machines,
vehicles and structures.
ISO 14839 consists of the following parts, under the general title Mechanical vibration — Vibration of rotating
machinery equipped with active magnetic bearings:
— Part 1: Vocabulary
— Part 2: Evaluation of vibration
The following part is under preparation:
— Part 3: Evaluation of stability margin.
©
iv ISO 2004 – All rights reserved
Introduction
This part of ISO 14839 concerns steady-state values of rotor vibrations and the AMB coil currents and voltage
measured during nominal steady-state operation, but not the transient condition while passing critical speeds.
The regulations of these transient vibrations passing at the critical speeds are established in ISO 10814 in
which the modal sensitivity, the so-called amplification factor (Q-factor), is then evaluated. This topic is beyond
the scope of this part of ISO 14839.
Because of the stiff support of oil-film bearings with small clearances [e.g. bearing radial clearance (C) divided
by the journal radius (R), C/R≈ 0,001], shaft vibration should be regulated within low levels to avoid oil-film
rupture of the lubricant and metal contact inside the bearing. In contrast, the relatively soft support of AMBs and
correspondingly large clearances (e.g. C/R≈ 0,005), a larger vibration level is often observed in AMB rotors,
but is quite normal and acceptable. The lower stiffness introduces no major problems in the transmission force
to the machine foundation. Compared to the oil-film bearing rotor standards (see the ISO 7919-1 series), this
part of ISO 14839 provides greater values of zone limits for vibration assessment and acceptance.
©
ISO 2004 – All rights reserved v
.
vi
INTERNATIONAL STANDARD ISO 14839-2:2004(E)
Mechanical vibration — Vibration of rotating machinery
equipped with active magnetic bearings —
Part 2:
Evaluation of vibration
1Scope
This part of ISO 14839 sets out general guidelines for measuring and evaluating rotating machinery equipped
with active magnetic bearings (AMBs) with respect to the following two indices:
— shaft vibratory displacement measured at or close to the AMBs, and
— working current and voltage measured in magnetic coils or power supply amplifiers.
Both indices are measured under nominal operating conditions in house and/or on site. These guidelines are
presented in terms of both steady-state running values of these indices and any magnitude changes which may
occur in these steady-state operations.
This part of ISO 14839 is applicable to industrial rotating machines generating or consuming nominal power
greater than 15 kW, and is not limited by size or operational rated speed (i.e. comprising turbo-compressors,
turbo-pumps, steam turbines, turbo-generators, turbo-fans, electric drives and other rotors supported by AMBs).
This part of ISO 14839 establishes the vibration, current and voltage evaluation of the rotating machinery
equipped with AMBs, specified by a comparatively large power capacity as described above, excluding small-
scale rotors such as turbo-molecular pumps, spindles and flywheels.
This part of ISO 14839 covers both AMB-equipped rigid rotors and AMB-equipped flexible rotors.
2 Normative references
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 any amendments) applies.
ISO 7919-1, Mechanical vibration of non-reciprocating machines — Measurements on rotating shafts and
evaluation criteria — Part 1: General guidelines
3 Measurement and evaluation procedures
3.1 Description of rotor-AMB system
A typical rotor system supported by AMBs is illustrated in Figure 1. An AMB is located at each end of the shaft
and includes an adjacent displacement transducer and an emergency (auxiliary) ball bearing. The axial AMB is
omitted in this figure. The control network for driving the AMB device is shown in Figure 2. As shown in these
figures, each displacement transducer detects the shaft journal position at the bearing locations and its signal is
fed back to the controller. Deviation from the bearing centre is delivered to the controller. This controller might,
for example, implement a proportional, integral and differential actions (PID) control algorithm. The controller
drives the power amplifiers to supply the coil current. If the shaft moves downward, the upper electromagnetic
coil is activated to lift the rotor upward by the magnetic force. Since, in this manner, the magnetic force acts
©
ISO 2004 – All rights reserved 1
upon the shaft so as to maintain the shaft at the neutral position inside the bearing, the AMB accomplishes both
levitation and vibration control without mechanical contact.
Key
1AMB
2 displacement transducer
3 touch-down bearing
4 clearance
Figure 1 — Rotor system equipped with active magnetic bearings
3.2 Displacement
Throughout this part of ISO 14839, the term “vibratory displacement” refers to the total displacement of the
shaft from the bearing's centre, including any static displacement. The vibration measurement of the stationary
parts of the machine (e.g. bearing housing) is excluded from this part of ISO 14839.
AMB equipment in rotating machines has its own displacement transducers for detecting shaft movement, x(t)
y(t)
and , as shown in Figure 3. No additional displacement transducers are required. The detected values of
shaft vibratory position by these displacement transducers is the subject of this part of ISO 14839.
©
2 ISO 2004 – All rights reserved
Key
1AMB
2 displacement transducer
3 power amplifier
4 controller
5 journal position signal
6 reference signal
Figure 2 — Layout of AMB control network
Key
1casing
2shaft
3 displacement transducers
Figure 3 — Displacement transducers of AMBs
©
ISO 2004 – All rights reserved 3
As shown in Figure 3, the displacement transducers are oriented in the xy and directions at each radial
bearing. The signals from these displacement transducers indicate the rotor journal position including the d.c.
component (eccentricity) and a.c. component (vibration orbit) as shown in Figure 4. Eccentricities from the
clearance centre of the AMB (designated O–O ) in the xy and directions are designated ε ,ε , while the
j x y
vibration orbit amplitudes in the xy and directions are designated a ,a . The maximum displacement of the
x y
rotor from the clearance centre of the radial AMB, designated D , can be calculated from Equation (1) exactly
max
� �
�
2 2
D = max x (t)+y (t) (1)
max
or approximated by Equation (2), based on the orbit observation:
�
2 2
D ≈ x +y (2)
max
max max
where
x =ε +a
max x x
y =ε +a
max y y
This formula to estimate the maximum displacement in a certain direction will generally overestimate the exact
value with a maximum error of approximately 40 %.
The evaluation of D from Equation (1) and (2) using the signals measured by two displacement transducers
max
is relatively complex. A digital oscilloscope or other special instrument is required. As a simpler procedure, the
maximum value of the displacement values measured in two orthogonal directions is recommended as shown
in Figure 4, based on the waveform observation:
D � max[x ,y ] (3)
max max max
This equation will, in general, underestimate the displacement.
Any of these three displacement quantities may be agreed upon as the method of characterizing the maximum
displacement D . In order to avoid contact problems between the rotor and stators, the following formula
max
should be satisfied with a certain margin against the minimum radial clearance C :
min-radial
D
max min-radial
This D is the index used to evaluate the clearance margin in this part of ISO 14839.
max
For assessment in this part of ISO 14839, the axial movement, , of the rotor is measured to compare with the
z
minimum axial clearance C in the same manner as shown in Figure 4. In this case:
min-axial
D =z
max max min-axial
These measurements considering the radial and axial directions should be made under agreed conditions over
the operational speed and load ranges of the machine. These measurements should typically be made after
achieving agreed thermal and operating conditions. It should be noted that these D indexes are measured
max
only for the specified steady-state conditions including nominal slow changes in load. In addition,
measurements may also be taken when different conditions exist or during transient changes, for example,
during slow roll, warming-up speed, critical speeds or shut down. However, the result of these measurements
may not be suitable for this evaluation.
©
4 ISO 2004 – All rights reserved
a) Orbit
b) Vibration time history
a is the vibration orbit amplitude
t is the time
ε is the eccentricity from the clearance centre
a
Time for one revolution.
Figure 4 — Unfiltered shaft orbit and vibration time history
©
ISO 2004 – All rights reserved 5
3.3 Coil current and voltage
At the time of publication of this part of ISO 14839, there are not enough data to define a criterion that
guarantees the reliable operation of the electrical part of the AMB system concerning the working current and
voltage in the coils. These parameters are thus not put into the evaluation, but the corresponding information is
stated as guidelines in Annexes A to C.
4 Evaluation criteria
4.1 General
Two evaluation criteria are used to assess the journal displacement of AMBs. One criterion considers the
magnitude of the observed displacement; the second considers changes in magnitude, irrespective of whether
they are increases or decreases.
4.2 Criterion I
Reliable operation of AMB machines requires satisfaction of Equations (4) and (5) to avoid contact between
rotating and stationary parts of a machine (e.g. at AMB stators, adjacent displacement transducers, touch-down
bearings or labyrinth seals). The minimum radial clearance, C , can be defined by the minimum gap when
min
statically moving the rotor in any radial direction. The touch-down bearing gap is generally set to be by
C
min
design.
In the case of AMBs, this criterion is concerned with defining limits only for the journal displacement to maintain
the running clearance margin. Other concerns with bearing dynamic load and the transmitted force to stationary
structures, as stated in ISO 7919-1, are excluded due to the comparably soft and non-contact support of AMBs
rather than oil-film bearings. Therefore, the speed dependency of the limit values does not exist in this part of
ISO 14839 and these limit values shall be constant in the whole range of rated speeds.
ISO 7919-1 establishes vibration zone guidelines for oil-film bearings. The definitions of each zone are as
follows.
Zone A: The vibratory displacement of newly commissioned machines would normally fall within this zone.
Zone B: Machines with vibratory displacement within this zone are normally considered acceptable for
unrestricted long-term operation.
Zone C: Machines with vibratory displacement within this zone are normally considered unsatisfactory for long-
term continuous operation. Generally, the machine may be operated for a limited period in this condition until a
suitable opportunity arises for remedial action.
Zone D: Vibratory displacement within this zone is normally considered to be sufficiently severe to cause
damage to the machine.
The corresponding zone table for magnetic bearings, established from international experience, is given in
Table 1. The corresponding graphical descriptions are provided in Figure 5.
These values are not intended to serve as an acceptance specification on either a test stand or the
commissioning installation. The acceptance specification shall be subject to agreement between the machine
manufacturer and customer. However, the values in Table1 provide guidelines for ensuring that gross
deficiency or unrealistic requirements are avoided. The values in Table 1 may also provide guidance for
condition monitoring, problem diagnosis and for setting operating limits. It should be noted that general
information on alarm and trip operating limits is stated in ISO 7919-1.
©
6 ISO 2004 – All rights reserved
Table 1 — Recommended criteria of zone limits
Zone limit Displacement D
max
A/B < 0,3C
min
B/C < 0,4C
min
C/D < 0,5C
min
NOTE C is the minimum value of radial or axial clearance between rotor and stator.
min
Key
X minimum radial clearance, C , in micrometres
min
Y maximum peak displacement, D , in micrometres
max
a
Ratio .D /C
max min
Figure 5 — Zone limits for vibration criteria
4.3 Criterion II
This criterion provides an assessment of the change in the vibration magnitudes from a baseline. A significant
change in broad-band magnitude may occur which would require some action even though zone C of Criterion I
has not been reached. Such changes can be progressive with time or instantaneous, and may point to incipient
damage or some other irregularity.
Criterion II is specified on the basis of the change in broad-band magnitude occurring under steady-state
operating conditions. When Criterion II is applied, it is essential that the measurements being compared be
taken under approximately the same machine operating conditions. Significant changes from the normal
magnitudes should be regulated to less than 25 % of the upper boundary value of zone B, as defined in Table 1,
because a potentially serious fault may be indicated. When the change in the magnitudes is beyond this
criterion, the reason for the change shall be determined, and any further action required shall be decided.
©
ISO 2004 – All rights reserved 7
Annex A
(informative)
Case study on an LP centrifugal compressor equipped with
active magnetic bearings (AMBs)
A.1 LP centrifugal compressor
The characteristics of a low-pressure (LP) compressor supported by AMBs are used as an example. The
compressor geometry is shown in Figure A.1, including eigen mode shapes obtained by assuming average
values of the AMB supporting stiffness. The LP compressor has seven stage impellers with a rotor mass of
780 kg. The design specification for this process compressor is shown in Table A.1. The rated speed is
10 900 r/min(182 Hz), with a nominal shaft power of 4 120 kW.
The AMB specification is shown in TableA.2. These radial AMBs are specified by
D/L= 0,98, C/R= 0,006 8, where the AMB journal length L= 150 mm, journal diameter D = 147 mm,
radial clearance C = 500µm, radius R=D/2.
Note that the radial clearance of the auxiliary bearing, 230µm, is set at about half the AMB clearance to prevent
emergency contacts of the AMB itself. Therefore, the minimum radial clearance C = 230µm is applicable in
min
accordance with this part of ISO 14839.
Key
1 first eigen mode
2 second eigen mode
3 third eigen mode
4 fourth eigen mode
5AMB
NOTE The operational speed N is set between the 3rd and 4th critical speeds. The AMB locations are offset from the
nodes of each eigen mode to maintain sufficient controllability.
Figure A.1 — Eigen mode shapes of LP rotor
©
8 ISO 2004 – All rights reserved
Table A.1 — Compressor design specification
Service LP casing HP casing
Model MCH 527 MCH 508
Gas Enriched H
3 3
Flow 43 69
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...