Frequency Converter Operation; Thermal Protection; Pump Controllers - Grundfos DWK Installation And Operating Instructions Manual

Pos. Description
IP Input power
CP Control panel
P Pump
1. T/P: thermal switch
N1
2. S/S: seal sensor
A Auto
M Manual
O Off
I On
SR/S Start-stop
OL Overload
RU Run
S Stop
F Fault
Y Yellow
R Red
G Green
RES Reset
N2 F/L: level controller

5.2 Frequency converter operation

Frequency converter is available only for
the DWK.E and DWK.H versions, for all
sizes. DWK.O cannot be operated with
frequency converter.
In principle, all three-phase motors can be connected
to a frequency converter. However, frequency
converter operation often exposes the motor
insulation system to a heavier load and causes the
motor to be noisier. In addition, large motors driven
with a frequency converter are loaded by bearing
currents.
For frequency converter operation, observe the
following:
• The thermal protection of the motor must be
connected.
• Peak voltage and dU/dt must be according to the
table below. The values stated are maximum
values supplied to the motor terminals. The cable
influence is not taken into account. See the
frequency converter data sheet regarding the
actual values and the cable influence on the peak
voltage and dU/dt.
• Use a screened power cable if there is a risk that
electrical noise may disturb other electrical
equipment.
• Set the frequency converter U/f ratio according to
the motor data.
14
• The locked-rotor torque can be lower depending
on the type of the frequency converter.
• The noise level may increase. See the installation
and operating instructions of the selected
frequency converter.
• Minimum switching frequency is 2 kHz. Variable
switching frequency is accepted.
• Do not exceed the frequency indicated on the
nameplate as this may cause motor overload.
• Keep the power cable as short as possible. The
peak voltage increases with the length of the
power cable.
• Use input and output filters on the frequency
converter.
• Do not reduce the motor speed to less than 30 %
of the rated speed.
• Keep the flow velocity above 1 m/sec.
• Let the pump run at rated speed at least once a
day to prevent sedimentation in the pipe system.
Maximum repetitive peak
voltage
[V]
850
Frequency converter use may reduce life
span of the bearings and the shaft seal,
depending on the operating mode and
other circumstances.

5.3 Thermal protection

One thermal switch is built into the motor winding to
break the circuit in case of overheating.
The following thermal protections are available for
DWK pumps, depending on the pump type:
• PTO or Klixon thermal switch (Bi-metallic)
• circuit breaker - Klixon (connected to the star point
of the stator)
• Pt100 thermal sensor (PCA Platinum chip).
Connect the thermal switch to the control wire of the
power cable inside the pump and to the safety circuit
of the separate pump controller.

5.4 Pump controllers

5.4.1 Level controllers
The liquid level can be controlled by the Grundfos LC
level controllers.
Suitable level controllers, depending on the size of
pumps:
• LC 231: a compact solution with certified motor
protection for a nominal current of up to 12A (9.6A
in the US) when running a single pump, or up to
9A (7.6A in the US) when running two pumps
simultaneously. Supports the DOL starting
method.
Maximum dU/dt U 400 V
N
[V/μ sec.]
2000