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3 Mechanical function 3.2 Power transmission
3.2.1 Motor and starter
The separator has a flexible coupling and for this
reason the motor must be able to endure long
run-up times. For this purpose the separator is
equipped with one of following two motor types:
CT motor
This motor has been designed by Alfa Laval as
“Control-torque motor” - abbreviated to CT motor.
The motor has some extra features compared
with a standard three phase motor with the same
kW rating. It has a higher class of insulation, a
higher rotor resistance and larger iron masses.
These features counteract the temperature rise in
the motor when starting. Furthermore, the motor
is provided with thermal sensors in the form of
thermistors in the stator windings. The
thermistors must be connected to a special
tripping device in the starter.
The overload protection (e.g. in the form of
bimetal relays) in the starter must be connected
into the D circuit. The protection must be
inoperative during the run-up period.
Frequency drive motor
This motor is similar to a standard three phase
motor. The long running up time is, however,
controlled by a frequency converter.
View of a CT motor
1. Thermistors Run-up period: Y-connected
Operation: D-connected
G0665121
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