Siemens SIRIUS 3RT - Page 155

Configuration
6.13 Starting three-phase motors with reduced starting current peaks (contactor assembly for star-delta (wye-
delta) start)
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
155
Preferred wiring not used
The motor also rotates clockwise if the motor terminals are connected as follows: phase L1
to motor terminals U1 and W2, L2 to V1 and U2, and L3 to W1 and V2.
Figure 6-7 Motor phases connected incorrectly results in clockwise rotation
The remanent
and decaying residual voltage becomes effective in the stator once more. The
phase winding with phasor U
L1’-N
is now connected to the line phase U
L1-L2
on switching to
delta. However, these two voltages have totally different vectorial directions; differential
voltage ΔU is high and produces a correspondingly high switchover current peak.
A switchover from star to delta results in the phasor diagram below.
1
Rotating field
2
Rotor's overtravel during the current-free phase
Figure 6-8 Phasor diagram for motor phase connections made according to the previous diagram
results in a high switchover current peak