Pump Controllers; Variable Frequency Drive Operation - Grundfos KPL Installation And Operating Instructions Manual

9.3 Pump controllers

The KPL, KWM pumps can be connected to a separate Grundfos
pump controller for level control, which is available as an
accessory:
• type LC for one-pump installations
• type LCD for two-pump installations
• Grundfos Dedicated Controls for one to six pumps.
Depending on the application, different types of level control
equipment can be used:
The LC controller is fitted with two or three level switches.
Two for start and stop of the pump. The third level switch, which
is optional, is for high-level alarm.
The LCD controller is fitted with three or four level switches.
One for common stop and two for start of the pumps. The fourth
level switch, which is optional, is for high-level alarm.
Grundfos Dedicated Controls are control systems designed for
installation in either commercial buildings or network pumping
stations with up to six pumps. Advanced control and data
communication is also possible with Grundfos Dedicated Controls
systems.
The Grundfos Dedicated Controls system consists of the
following components:
• CU 361 control unit
• IO 351B module (general I/O module)
• IO 113 protection module (optional).
Grundfos Dedicated Controls systems starts/stop pumps by
means of the following devices:
• float switches
• analog pressure sensors
• ultrasonic sensors.
Furthermore, it is possible to control the water level by combining
float switches with an analog pressure sensor. Two additional
safety float switches can be installed in the Dedicated Controls
system for high-level and dry-running alarm.

10. Variable frequency drive operation

In principle, all three-phase motors can be connected to a
variable frequency drive.
However, variable frequency drive operation will often expose the
motor insulation system to a heavier load and cause the motor to
be more noisy than usual due to eddy currents caused by voltage
peaks.
For variable frequency drive operation, please observe the
following:
• Requirements must be fulfilled.
• Recommendations ought to be fulfilled.
• Consequences should be considered.
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 the
motor terminals. The cable influence has not been taken into
account. See the variable frequency drive data sheet
regarding the actual values and the cable influence on the
peak voltage and dU/dt.
Maximum repetitive peak
voltage (400 V / 460 V)
[V]
850
• Set the variable frequency drive U/f ratio according to the
motor data.
• Local regulations/standards must be fulfilled.
Recommendations
Before installing a variable frequency drive, calculate the lowest
allowable frequency in the installation in order to avoid zero flow.
• Do not reduce the motor speed to less than 25 % of rated
speed.
• Keep the flow velocity above 3.3 ft/sec; recommended
minimum velocity ~3 ft./sec.
• If the pumping liquid is available, then the pump should be 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 as
this may cause 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 variable frequency drive used.
• Use input and output filters on the variable frequency drive.
See data sheet for the variable frequency drive used.
• Use a screened motor cable if there is a risk that electrical
noise may disturb other electrical equipment. See data sheet
for the variable frequency drive used.
Consequences
When operating the pump via a variable frequency drive, please
be aware of these possible consequences:
• The locked-rotor torque will be lower; how much lower will
depend on the variable frequency drive type. See the
Installation and Operating Instructions for the variable
frequency drive used, for information on the locked-rotor
torque available.
• The acoustic noise level may increase. See the Installation
and Operating Instructions for the variable frequency drive
used, for advice as to how to reduce the acoustic noise.
Maximum dU/dt
U (400 V - 460 V)
N
[V/μ sec.]
2000
13