Grundfos SP Installation And Operating Instructions Manual page 17

6.7.3 Variable-frequency drive operation
Grundfos motors
Three-phase Grundfos motors can be connected
to a variable frequency drive (VFD).
If a Grundfos MS motor with
temperature transmitter is connected
to a variable frequency drive, a fuse
incorporated in the transmitter will
melt, and the transmitter will be
Note
inactive. The transmitter cannot be
reactivated. This means that from that
point on, the motor will operate like a
motor without a temperature
transmitter.
If a new temperature transmitter is required, a
Pt100/1000 sensor for fitting to the submersible
motor can be ordered from Grundfos.
During variable-frequency drive operation, we
recommend that you do not run the motor at a
frequency higher than the nominal frequency (50
or 60 Hz) and not lower than 30 Hz. In
connection with pump operation, it is important
never to reduce the frequency (and
consequently the speed) to such a low level that
the necessary flow of cooling liquid past the
motor is no longer ensured.
To avoid damage to the pump, make sure that
the motor stops when the pump flow falls below
0.1 x rated flow.
Depending on the type of variable frequency
drive, it may expose the motor to detrimental
voltage peaks.
The variable frequency drive must have some
kind of output sine-wave filter to limit voltage
peaks (Upeak) and to reduce dU/dt (or dV/dt)
which causes stress on the insulation of the
submersible motor. For sine-wave filter location
placement within the system, see fig. 13.
CAUTION
We recommend that you protect your
motor from voltage peaks (Upeak)
and excess dU/dt (or dV/dt) by using
a sine-wave filter if one or more of the
following conditions are present:
• The motor nameplate voltage is
above 379 V.
• The variable frequency drive (VFD)
uses pulse width modulation
(PWM) and/or IGBT-BJT switches.
• The VFD voltage rise time is less
than 2 msec (NEMA MG 1-2011).
Caution
• The power cable length from the
VFD to the submersible motor
terminals is 0 to 1500 ft (0 to 457
m).
• The power quality is not stable.
• Keep the motor peak voltage
(U ) and dU/dt within the limits
peak
listed in the table below.
For recommended best practice, use
a resistor-inductor-capacitor (RLC)
type sine-wave filter. An equivalent
type LC sine-wave filter is acceptable.
Consult the VFD manufacturer for
specific sine-wave filter
recommendation.
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