English (GB)
8
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 a temperature transmitter is required, a Pt100
sensor for fitting to the submersible motor can be
ordered from Grundfos.
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.
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.
Single-phase MS 4000 submersible motors must be
protected. A protective device can either be
incorporated in a control box or be separate.
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.
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.
Motor type
Max. U
peak
voltage
Max. dU/dt
MS 402
650 V
phase-phase
2000 V/μs
MS 4000
850 V
phase-phase
2000 V/μs
MS 6000
850 V
phase-phase
2000 V/μs
MMS6
850 V
phase-ground
500 V/μs
MMS 8000
850 V
phase-ground
500 V/μs
MMS 10000
850 V
phase-ground
500 V/μs
MMS 12000
850 V
phase-ground
500 V/μs
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.
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.
www.motralec.com / service-commercial@motralec.com / 01.39.97.65.10
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