Frequency Converter Operation - Grundfos SEG Serie Montage- Und Betriebsanleitung

8.5 Frequency converter operation

For frequency converter operation please observe
the following information.
Requirements must be fulfilled.
Recommendations ought to be fulfilled.
Consequences should be considered.
Frequency converter operation will
Note
influence the efficiency of the grinder
system.
8.5.1 Requirements
• 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 motor terminals.
The cable influence has not been taken into
account. See data sheet for the frequency
converter used regarding the actual values and
cable influence on the peak voltage and dU/dt.
Max. repetitive peak
voltage
[V]
650
• If the pump is an Ex-approved pump, check if the
Ex certificate of the specific pump allows the use
of frequency converter.
• Set the frequency converter U/f ratio according to
the motor data.
• Local regulations/standards must be fulfilled.
8.5.2 Recommendations
Before installing a frequency converter, calculate the
lowest allowable frequency in the installation in order
to avoid zero flow.
• Do not reduce the motor speed to less than 30 %
of rated speed.
• Keep the flow velocity above 1 m/sec.
• Let the pump run at rated speed at least once a
day in order to prevent sedimentation in the
piping system.
• Do not exceed the frequency indicated on the
nameplate. In this case there is risk of motor
overload.
• Keep the motor cable as short as possible.
The peak voltage will increase with the length of
the motor cable. See data sheet for the frequency
converter used.
• Use input and output filters on the frequency
converter. See data sheet for the frequency
converter used.
• Use screened motor cable if there is a risk that
electrical noise can disturb other electrical
equipment. See data sheet for the frequency
converter used.
18
8.5.3 Consequences
When operating the pump via a frequency converter,
please be aware of these possible consequences:
•
•
•
Max. dU/dt
U 400 V
N
[V/μ sec.]
2000
The locked-rotor torque will be lower. How much
lower will depend on the frequency converter
type. See the installation and operating
instructions for the frequency converter used for
information on the locked-rotor torque available.
The working condition of bearings and shaft seal
may be affected. The possible effect will depend
on the application. The actual effect cannot be
predicted.
The acoustic noise level may increase. See the
installation and operating instructions for the
frequency converter used for advice as to how to
reduce the acoustic noise.