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.
Maximum repetitive
peak voltage
[V]
Maximum dU/dt U
N
400 V
[V/μ sec.]
850 2000
Frequency converter use
may reduce the lifespan
of the bearings and the
shaft seal, depending on
operating mode and oth-
er circumstances.
For more information about the frequency converter
operation, see the data sheet and the installation and
operating instructions for the selected frequency
converter.
Pump controllers
The pumps can be controlled by the Grundfos LC
231, LC 241, DC and DCD controllers.
Pumps with a sensor are supplied with an IO 113,
which can receive signals from the following
transmitters:
• water-in-oil (WIO) sensor in the pump
• moisture sensor in the motor
• temperature sensor in the stator windings
• winding resistance sensor in the motor.
For further information, see installation and operating
instructions for the specific sensor.
Level controllers
The pump must not run
dry.
Install an additional level
switch to ensure that the
pump is stopped in case
the stop level switch is
not operating.
The pump must be stop-
ped when the liquid level
reaches the upper edge
of the clamp.
19
English (GB)
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