Manual for Induction Motors and Generators
Maintenance - 67
3BFP 000 050 R0101 REV E
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Figure 7-1 Measuring points
7.4.3.2 Classification according to support flexibility
Two conditions are used to classify the support assembly flexibility in specified directions:
• rigid supports
• flexible supports
These support conditions are determined by the relationship between the machine and
foundation flexibilities. If the lowest natural frequency of the combined machine and support
system in the direction of measurement is higher than its main excitation frequency (this is in
most cases the rotational frequency) by at least 25 %, then the support system may be
considered rigid in that direction. All other support systems may be considered flexible.
7.4.3.3 Evaluation
ISO 10816-1 provides a general description of the two evaluation criteria used to assess
vibration severity on various classes of machines. One criterion considers the magnitude of
observed broad-band vibration; the second considers changes in magnitude, irrespective of
whether they are increases or decreases.
Evaluation zones
The following evaluation zones are defined to permit a qualitative assessment of the vibration of
a given machine and provide guidelines on possible actions.
Zone A: The vibration of newly commissioned machines would normally fall within this zone.
Zone B: Machines with vibration within this zone are normally considered acceptable for
unrestricted long-term operation.
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