Frequency Converter Operation - Grundfos SE1 50 Installation And Operating Instructions Manual

6.1 Frequency converter operation

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 due to eddy
currents caused by voltage peaks.
In addition, large motors operated with a frequency
converter are loaded by bearing currents.
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.
• Minimum switching frequency is 2.5 kHz. Variable
switching frequency is accepted.
• If the pump is Ex-approved, 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 30 %.
• 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 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 type of the frequency converter.
• The noise level may increase. See the installation
and operating instructions for the selected
frequency converter.
18
Maximum repetitive
Maximum dU/dt U
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.
For more information about the frequency converter
operation, see the data sheet and the installation and
operating instructions for the selected frequency
converter.
400 V
N
[V/μ sec.]
2000