Functional Principle Of The Sirius 3Rw30 And 3Rw40 Soft Starters - Siemens SIRIUS 3RW30 Manual

Product description

3.2 Functional principle of the SIRIUS 3RW30 and 3RW40 soft starters

3.2 Functional principle of the SIRIUS 3RW30 and 3RW40 soft starters
The SIRIUS 3RW30 and 3RW40 soft starters have two antiparallel thyristors in two out of the
three phases. One thyristor for the positive half-wave and one for the negative half-wave is
provided in each phase (refer to Fig. "Phase angle control and schematic diagram of a two-
phase controlled soft starter with integral bypass contacts"). The current in the third,
uncontrolled phase is the sum of the currents in the controlled phases.
The rms value of the motor voltage is increased (from a settable starting voltage) to the rated
motor voltage within a definable starting time by means of the phase angle control.
The motor current changes in proportion to the voltage applied to the motor. As a result, the
starting current is reduced by the factor of this voltage.
There is a quadratic relationship between the torque and the voltage applied to the motor. As
a result, the starting torque is reduced quadratically in relation to this voltage.
Example
SIEMENS 1LG4253AA motor (55 kW)
Rated data at 400 V
P :
e
I :
e
I
direct starting
M :
e
n :
e
M
direct starting
Set starting voltage:
=> I
=> M
24
:
:
½ of direct starting current (approx. 350 A)
starting
¼ of direct starting torque (approx. 175 Nm)
starting
55 kW
100 A
Approx. 700 A
355 Nm; e.g.: M = 9.55 x 55 kW x
e
1480 rpm
Approx. 700 Nm
50 % (½ of mains voltage)
Manual, 10/2018, NEB535199502000/RS-AB/005
SIRIUS 3RW30 / 3RW40