Manual for Induction Motors and Generators
68 -
Maintenance
3BFP 000 050 R0101 REV E
Zone C: Machines with vibration 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: Vibration values within this zone are normally considered to be of sufficient severity to
cause damage to the machine.
Operational limits
For long-term operation, it is common practice to establish operational vibration limits. These
limits take the form of ALARMS and TRIPS.
Setting of ALARMS
The ALARM values may vary considerably, up or down, for different machines. The values
chosen will normally be set relative to a baseline value determined from experience for the
measurement position or direction for that particular machine.
It is recommended that the ALARM value should be set higher than the baseline by an amount
equal to 25 % of the upper limit for zone B. If the baseline is low, the ALARM may be below
zone C.
Setting of TRIPS
The TRIP values will generally relate to the mechanical integrity of the machine and be
dependent on any specific design features which have been introduced to enable the machine to
withstand abnormal dynamic forces. The values used will, therefore, generally be the same for
all machines of similar design and would not normally be related to the steady-state baseline
value used for setting ALARMS.
Table 7-3. Classification of vibration severity zones for large machines with rated power
above 300 kW and not more than 50 MW; electrical machines with shaft height H
/
315 mm or
higher
7.5 Maintenance of bearings and lubrication system
This chapter covers the most important maintenance tasks in the bearings and in the lubrication
system.
Support class
Zone boundary
R.m.s. velocity
[mm/s]
Rigid
A/B
B/C
C/D
2.3
4.5
7.1
Flexible
A/B
B/C
C/D
3.5
7.1
11.0
