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

6.1 Frequency converter operation

6.1.1 Grundfos motors
Three-phase Grundfos motors can be connected to a frequency
converter.
If an MS motor with temperature transmitter is
connected to a frequency converter, a fuse
incorporated in the transmitter will melt and the
transmitter will be inactive. The transmitter cannot be
reactivated. This means that the motor will operate
like a motor without a temperature transmitter.
If a temperature transmitter is required, Grundfos offers a Pt100
or Pt1000 sensor for the submersible motor.
During frequency converter operation, it is not
advisable to run the motor at a frequency higher than
the rated frequency (50 or 60 Hz). In connection with
pump operation, it is important never to reduce the
frequency (and consequently the speed) to such a
level that the necessary flow of cooling liquid past the
motor is no longer ensured.
To avoid damage to the pump part, the motor must stop when the
pump flow falls below 0.1 x nominalflow
Depending on the frequency converter type, it may expose the
motor to detrimental voltage peaks.
To avoid damage to the pump part, make sure that the motor stops when
the pump flow falls below 0.1 x rated flow.
Depending on the type, the frequency converter may cause increased
acoustic noise from the motor. Furthermore, it may expose the motor to
detrimental voltage peaks.
This can be avoided by installing a correctly dimensioned sinus filter
between the frequency converter and the motor.
Grundfos recommends installing a sinus filter when a frequency converter
is used.
Voltage peaks for Grundfos submersible motors should be limited in
accordance with the table below.
Max. Upeak
Motor type
voltage
650 V
MS 402
phase-phase
850 V
MS 4000
phase-phase
850 V
MS 6000
phase-phase
850 V
MMS6
phase-ground
850 V
MMS 8000
phase-ground
850 V
MMS 10000
phase-ground
850 V
MMS 12000
phase-ground
To enable monitoring of the motor temperature when running
at frequency converter operation, Grundfos recommends
installing a Pt100 sensor together with a PR 5714 relay.
Permissible frequency ranges: 30-50 Hz and 30-60 Hz.
Ramp times: Maximum 3 seconds for start and stop.
We recommend that you protect other motors against voltage
peaks higher than 850 V.
The above disturbance can be abated by installing an RC filter
between the frequency converter and the motor.
Possible increased acoustic noise from the motor can be abated
by installing an LC filter which will also eliminate voltage peaks
from the frequency converter.
We recommend that you install an LC filter when using a
frequency converter. See section 6.7.5 Frequency converter
operation.
For further details, contact your frequency converter supplier or
Grundfos.
Max. dU/dt
2000 V/μs
2000 V/μs
2000 V/μs
500 V/μs
500 V/μs
500 V/μs
500 V/μs
6.1.2 Other motor makes than Grundfos
Contact Grundfos or the motor manufacturer.
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