3RW3 semiconductor motor control unit
SIRIUS System Manual
GWA 4NEB 430 0999-02b
8-7
Star-delta starter
After a delay, the motor windings are switched from a star to a delta config-
uration. The motor current for star starting is only about 1/3 of that required
for delta starting (motor torque, too, is reduced to approximately 1/3 of the
delta torque).
Disadvantages:
• 6 motor cables are necessary
• Switching surges occur (in the current and torque transients)
• The startup cannot be adapted to the system environment
• Installation is relatively complicated and time-consuming
• More space is needed in the cubicle
Figure 8-2: Current and torque curves for star-delta starting
I
I
A
d
I
A
*
=
Starting current for
d
Starting current
for
*
/
d
-start
n
n
n
syn
*
n
rated
M
M
A
d
M
motor for
d
M
motor for
*
M
A
*
=1/3 M
A
d
M
load
n
n
n
syn
*
n
rated
1/3 I
A
d
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