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6. Operating conditions
6.1 Ambient temperature and installation altitude
Grundfos motors are designed for operation at temperatures up
to 40 °C. Grundfos MG motors are capable of continuous
operation at ambient temperatures up to 60 °C, however subject
to a shorter bearing life. See section 11.2 Motor bearings.
The ambient temperature and the installation altitude are
important factors for the motor life. The table below shows max.
ambient temperature and max. installation altitude.
The table does not show combined maximum values, meaning
that the motor is not capable of operating at +60 °C at an altitude
of 3500 m at the same time.
If these values are exceeded, the motor must not be fully loaded
due to the risk of overheating.
Overheating may result from excessive ambient temperatures or
low density and consequently low cooling effect of the air.
In such cases, it may be necessary to reduce the load or use a
motor with a higher rated output.
The curves below show the maximum motor load of the various
efficiency classes.
Fig. 1 Motor output in relation to temperature/installation
altitude
Example
The example shows an IE2 motor under these operating
conditions:
• Ambient temperature: 65 °C.
• Installation altitude above sea level: 4750 m.
Maximum load of the motor:
• Ambient temperature of 65 °C: 95 %.
• 4750 m above sea level: 88 %.
As both operating conditions apply, the motor must not be loaded
more than (0.95 x 0.88) = 83.6 %.
6.2 Frequency converter operation
All three-phase MG motors with phase insulation can be
connected to a frequency converter.
6.2.1 Phase insulation
MG 71 and 80
MG motors, frame sizes 71 and 80, do not have phase insulation
as standard. The motors are not suitable for frequency converter
operation as they are not protected against the voltage peaks
caused by frequency converter operation.
Only motors with a rated voltage equal to or above 460 V have
phase insulation.
MG 90 to 180
MG motors, frame sizes 90 to 180, have phase insulation.
The motors are suitable for frequency converter operation,
subject to these precautions:
Operating conditions for MG motors to be used for frequency
converter operation
• Supply voltage up to 400 V:
– Check that the motor has phase insulation.
(Only motors with a rated voltage equal to or above 460 V
have phase insulation.)
• Supply voltage above 400 V:
– Check that the motor has phase insulation.
(Only motors with a rated voltage equal to or above 460 V
have phase insulation.)
– Fit a sine-wave filter between the motor and the frequency
converter.
6.2.2 Acoustic noise and voltage peaks
Frequency converter operation may cause increased acoustic
noise from the motor and will often expose the motor insulation
system to a heavier load due to voltage peaks reducing motor life.
To prevent the voltage peaks from damaging the motor, make
sure to observe the limits of IEC 60034-17.
Increased acoustic noise and detrimental voltage peaks can be
eliminated by fitting an output filter between the frequency
converter and the motor. For further details, contact your
frequency converter supplier or Grundfos.
Figure 2 shows the maximum permissible voltage peaks
measured at the motor terminals for a specific rise time.
Fig. 2 Maximum values for voltage peaks
Efficiency class
Max. ambient
temperature at full
load
[°C]
Max. installation
altitude above sea
level at full load
[m]
NA +40 1000
IE2
+60 3500
IE3
TM05 1168 2311
If the motor load is not reduced in case the
ambient temperature or installation altitude is
exceeded, the motor life will be limited, and the
warranty is void.
50
60
70
80
90
70656055504540353025 8075
Frequency converter operation of MG motors
without phase insulation will cause damage to
the motor.
TM04 4556 1709
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
t [mS]
800
900
1000
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1400
U [V]
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