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8.4 Thermal switches
All pumps have two sets of thermal switches
incorporated in the stator windings.
The thermal switch in circuit 1 (T1-T3) will break the
circuit at a winding temperature of approx. 150 °C.
This thermal switch must always be connected.
The thermal switch in circuit 2 (T1-T2) will break the
circuit at a winding temperature of approx. 170 °C,
three-phase pumps, or 160 °C, single-phase pumps.
Maximum operating current of the thermal switches
is 0.5 A at 500 VAC and cos
φ
0.6. The switches
must be able to break a coil in the supply circuit.
In the case of standard pumps, both thermal
switches can (when closing the circuit after cooling)
generate automatic restarting of the pump via the
controller.
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.
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.
•
If the pump is an Ex-approved pump, check if the
Ex certificate of the specific pump allows the use
of a frequency converter.
•
Set the frequency converter U/f ratio according to
the motor data.
•
Local regulations and 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 power cable as short as possible. The
peak voltage will increase with the length of the
power 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 a screened power cable if there is a risk that
electrical noise can disturb other electrical
equipment. See data sheet for the frequency
converter used.
8.5.3 Consequences
When operating the pump via a frequency converter,
please be aware of these possible consequences:
•
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 on how to
reduce the acoustic noise.
After thermal cutout, explosion-proof
pumps must be restarted manually. The
thermal switch in circuit 2 must be
connected for manual restarting of these
pumps.
DANGER
Explosive environment
Death or serious personal injury
- Do not install the separate motor-
protective circuit breaker or control box
in potentially explosive environments.
Max. repetitive peak
voltage
[V]
Max. dU/dt
U
N
400 V
[V/
μ
sec.]
650
2000
