30
Motor
Manual
8 Frequency converter operation
By using a VFD with Hoyer motors, you get optimal operat-
ing conditions of your system. Not only will a VFD-solution
increase energy savings, but also reduce application noise
and thus give crucial improvements to the surrounding
working environment. A VFD will secure a precise motor
application control, which ensures optimal application
performance and a reduction in mechanical stress on the
system, thus extending the system lifetime.
When operating your motor with a frequency converter,
please be aware of below.
8.1 Operating speed
Controllable operating speed will most likely lead to an
optimized application performance and overall system
efficiency. By using VFD control it is possible to drive the
motor and application at a wide range of speeds. When
controlling the speed of a motor, please take these general
conditions into account.
1) When operating below nominal speed, the cooling ca-
pacity of the motor will be reduced and could result in
potential overheating.
2) When operating above nominal speed, the output
torque will be reduced, which can complicate the di-
mensioning of the motor for a given application.
3) When operating above nominal speed, the critical
speed of the shaft-rotor must be taken into account, es-
pecially for larger motors with low pole numbers. For
continuous speeds outside the values given in Table 1,
please contact Hoyer.
Motor size 2 pole 4 pole 6 pole
71 6000 3600 2400
80 6000 3600 2400
90 6000 3600 2400
100 6000 3600 2400
112 4500 3600 2400
132 4500 2700 2400
160 4500 2700 2400
180 4500 2700 2400
200 4500 2300 1800
225 3600 2300 1800
250 3600 2300 1800
280 3600 2300 1800
315 3600 2300 1800
355 3600 2300 1800
400 3600 1800 1200
450 3000 1800 1200
Table 12: Maximum operating speed [RPM]
Please contact Hoyer for confirmation of speeds above 60
Hz for continuous operation. VFD-curves for Hoyer mo-
tors are available on http://hoyermotors.com.
8.2 Winding insulation
When using a VFD voltage peaks are generated which in-
creases the electrical deterioration of the motor insula-
tion system. To prevent deterioration and to extend the
lifetime of the motor insulation system, reinforced insu-
lation systems are recommended for VFD supply voltages
above 500 V. In some cases, filters are also recommended
at the output of the VFD’s. Hoyer’s three insulation sys-
tems are designed in accordance with IEC 60034-17 and
IEC TS 60034-25, which states the voltage stress withstand
capability as seen in below table.
Hoyer insulation system designation Electrical specification
Hoyer standard insulation 1350 V @ 0.8 µs
Hoyer reinforced insulation 1560 V @ 0.5 µs
Hoyer premium reinforced insulation 2150 V @ 0.5 µs
Table 13: The voltage stress withstand capability
8.3 Bearing deterioration in relation to VFD
Utilizing VFD control of an electric motor can introduce
increased risk of bearing currents. Persistent bearing cur-
rents will often result in mechanical deterioration of the
motor bearings and must therefore be avoided.
The following factors influence, but are not limited to, the
arise of persistent bearing currents:
• Motor sizes and construction.
• Specific application and duty.
• Bearing types.
• VFD switching frequency and mode.
• VFD output filters.
• Grounding of the shaft either through the application
or application bearings.
• Overall grounding installation and considerations re-
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