Frequency Converter Operation - Grundfos SMD Installation And Operating Instructions Manual

6.9 Frequency converter operation

All mixers and flowmakers are designed for frequency
converter operation for energy saving and for soft
start. However, frequency converter operation often
exposes the motor insulation system to a heavier load
and causes the motor to be more noisy.
In this product range, only negligible amounts of
bearing currents occur during frequency converter
operation.
For frequency converter operation, observe the
following:
• The thermal protection of the motor must be
connected.
• Peak voltage and dU/dt must be in accordance
with the table below. The values stated are
maximum values supplied to the motor terminals.
The cable influence is not taken into account. See
the frequency converter data sheet regarding the
actual values and the cable influence on the peak
voltage and dU/dt.
• Set the frequency converter U/f ratio according to
the motor data.
Product type
SMD
SMG.09-45
SFG.xx.130/180/230
SMG.48-185
SFG.xx.150/260
• In case the above values are too high, a dU/dt
filter could prevent the voltage peaks.
• The thermal protection of the motor must be
connected.
• Local regulations or standards must be complied
with.
• Do not reduce the motor speed to less than 30 %.
• Do not set any slip compensation, as it may lead
to an overspeed and therefore to motor overload.
• Set the frequency converter U/f ratio to a linear
relation, and use the data from the motor
nameplate to set the rated current, power, voltage
and frequency.
• Do not exceed the frequency indicated on the
nameplate as this may cause motor overload.
• Keep the power cable as short as possible. The
peak voltage increases with the length of the
power cable.
• Use input and output filters on the frequency
converter.
• Use a screened power cable if there is a risk that
electrical noise may disturb other electrical
equipment.
Maximum
Maximum
repetitive
dU/dt
peak volt-
[V/μs]
age [V]
1500 15000
1000 3000
• Ramp-up and ramp-down time must be at least
5-10 seconds.
When operating the pump by a frequency converter,
consider the following:
• The locked-rotor torque can be lower depending
on the frequency converter.
• The noise level may increase. See the installation
and operating instructions for the selected
frequency converter type.
Frequency converter use may reduce the
lifespan of the bearings and the shaft seal,
depending on operating mode and other
circumstances.
For explosion-proof products, the PTC
sensors placed in the windings must be
connected to a suitable relay with the ap-
propriate safety level (SIL 1).
If the motor is operated by a frequency
converter, the temperature class of the ex-
plosion-proof SMD mixer must be T3.
For more information about frequency con-
verter operated mixer or flowmaker speed
and torque curves, visit the Grundfos
Product Center at https://product-selec-
tion.grundfos.com.
For more information about the frequency converter
operation, see the data sheet and the installation and
operating instructions for the selected frequency
converter.
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