5 Start-up
5.2
5.3 Transient
behaviour
5.3.1 General
The fan can only be started when a
sufficiently high moment of acceleration is
available form the moment it is started up
to the moment when nominal speed is
reached.
It is recommended to start the fan with the damper
closed.
The customer has to check that his power
network, switchgear, monitoring devices (if
available) and cable cross sections are
dimensioned to cope with the transient
behaviour and current peaks.
5.3.2 Direct starting
Direct starting of the fan motor not only causes a
high starting torque but also a high starting current.
During starting the starting current may be 6 to 8
times as high as the nominal current (depending on
the type of rotor).
This high power input must be taken into account
when the fuse sizes are determined.
The connecting frequency of the electric motors
must not exceed six activations per hour. The
instructions of the motor manufacturer are to be
observed. Please contact the motor manufacturer
for further information if necessary
.
5.3.3 Star-delta starting
During star-delta starting the drive motor only
provides for 1/3 of the starting torque in the star
connection. At a certain starting speed the load
moment of the fan exceeds the starting torque of the
motor. The motor does not accelerate. At this point
the motor has to be changed over to the delta
connection. The current peak which is then obtained
is clearly lower than the one occurring during direct
starting.
Mm Motormoment
ML Loadmoment
Mbm Mean acclerating moment
n Speed
Designation of Mean accelerating moment
change over point
