Frequency Converter Operation - Grundfos S Series Installation And Operating Instructions Manual

4.3 Frequency converter operation

If the motor is operated by a frequency
converter, the temperature class of explo-
sion-proof pumps must be T3.
In principle, all three-phase motors can be connected
to a frequency converter.
However, frequency converter operation often
exposes the motor insulation system to a heavier load
and causes the motor to be more noisy than usual.
In this product range, only a negligible amount of
bearing currents occurs during the use of a frequency
converter.
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.
• switching frequency is 2 kHz. Variable switching
frequency is accepted.
• If the pump is an Ex-approved pump, check if the
Ex certificate of the specific pump allows the use
of a frequency converter.
• Set the frequency converter U/f ratio according to
the motor data.
• Local regulations or standards must be complied
with.
• Before installing a frequency converter, calculate
the lowest permissible frequency in the installation
to avoid zero flow.
• Do not reduce the motor speed to less than 50 %.
• Keep the flow rate above 1 m/sec.
• Let the pump run at rated speed at least once a
day to prevent sedimentation in the piping system.
• 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.
• Set the frequency converter for constant-torque
operation. Pulse width modulation should be
used.
When operating the pump by a frequency converter,
consider the following:
• The locked-rotor torque can be lower depending
on the frequency converter type.
• The noise level may increase. See the installation
and operating instructions for the selected
frequency converter.
Maximum repetitive
peak voltage
[V]
850
Frequency converter use may reduce the
lifespan of the bearings and the shaft seal,
depending on operating mode and other
circumstances.
Information about pump speed/torque
curves, when operated by frequency con-
verter, can be found on the Grundfos Prod-
uct 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.
Maximum dU/dt U
N
400 V
[V/μ sec.]
2000
23