Frequency Converter Operation; Motor Protection - Grundfos MS Montage- Und Betriebsanleitung

5.1.1 Frequency converter operation

Three-phase MS motors can be connected to a
frequency converter.
MMS motors with PE/PA 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
Caution
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, a Pt100
sensor for fitting to the submersible motor can be
ordered from Grundfos.
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
Caution 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, 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. U
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
Note
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.

5.2 Motor protection

5.2.1 Single-phase motors
Single-phase MS 402 submersible motors
incorporate a thermal switch and require no
additional motor protection. As a exception, the
1.1 kW (1.5 hp) MS 402 requires external current
protection.
Warning
When the motor has been thermally
switched off, the motor terminals are
still live. When the motor has cooled
sufficiently, it will restart automatically.
Single-phase MS 4000 submersible motors must be
protected. A protective device can either be
incorporated in a control box or be separate.
peak
Max. dU/dt
2000 V/μs
2000 V/μs
2000 V/μs
500 V/μs
500 V/μs
500 V/μs
500 V/μs
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