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6.6 Direction of rotation
When you have carried out the electrical connections, check that
the propeller is rotating in the correct direction. When viewed
from the motor, the propeller must rotate clockwise. An arrow on
the motor housing shows the correct direction of rotation.
If the propeller rotates in the wrong direction, interchange two
phases of the mains supply.
6.7 Protection against electro-chemical corrosion
Two different metals or alloys cause electro-chemical corrosion if
they are connected by an electrolyte. This applies if you install
more than one mixer or flowmaker in the same tank. We
recommend one of the following additional protection methods:
•
galvanic separation of the earth conductor from the neutral
conductor
•
galvanic separation of the mains supply by means of isolation
transformer
•
anode kit.
Separate the earth conductor in such a way that no direct current
can flow through it. It must still function as a protective conductor.
You achieve this with a limiting unit, polarization cell, anti-parallel
diode or an isolation transformer.
2
3
Fig. 33 Protection against electro-chemical corrosion
Pos.
Description
1
Limiting unit
2
Earth conductor
3
Isolation transformer
When you use an isolation transformer, do not alter
the ratio between starting current and rated current.
6.8 Frequency converter operation
All mixers and flowmakers are designed for frequency converter
operation for energy saving and for soft start. For frequency
converter operation, please observe the following:
•
Requirements must be fulfilled.
•
Recommendations ought to be followed.
•
Consequences ought to be considered.
6.8.1 Requirements
•
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 frequency converter data sheet regarding the
actual values and the cable influence on the peak voltage and
dU/dt.
Product type
SMD
SMG.12-55
SFG.xx.51/71/91
SMG.75-220
L1
SFG.xx.102
L2
L3
N
PE
•
In case the above values are too high, a dU/dt filter could
prevent the voltage peaks.
•
The thermal protection of the motor must be connected.
1
FM
2
•
Do not exceed the frequency indicated on the nameplate.
Otherwise, there is a risk of motor overload.
•
Local regulations or standards must be fulfilled.
6.8.2 Recommendations
•
Do not reduce the motor speed to less than 30 % of the rated
speed.
•
Do not set any slip compensation, as it may lead to overspeed
and therefore to motor overload.
•
Set the frequency converter U/f ratio to a linear relation, and
use the data from the motor nameplate to set rated current,
power, voltage and frequency.
•
Use input and output filters on the frequency converter. See
data sheet for the frequency converter used.
•
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 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.
Maximum repetitive
peak voltage
[V]
1500
1000
For explosion-proof products, the PTC or PTO
sensors placed in the windings must be connected to
a suitable relay with the appropriate safety level (SIL
1).
Maximum dU/dt
[V/μs]
15000
3000
19
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