2.3.1 Wye Connection
Figure 4a represents a three-phase wye-connected motor with
three sources connected to supply voltages, U
1,2,U2,3, and U3,1.
The SIKOSTART controller is connected in line with the motor
windings.
As can be seen, the source current, the SIKOSTART current, and
the motor winding current are all equal.
[-] = Vector Subtraction
U1, 2 = Ua [-] Ub
U2, 3 = Ub [-] Uc
U3, 1 = Uc [-] Ua
Ia = I1
Ib = I2
Ic = I3
U1, 2 = SqRt(3) * Ua
U2, 3 = SqRt(3) * Ub
U3, 1 = SqRt(3) * Uc
2.3.2 Delta Connection
Figure 4b represents a three-phase delta-connected motor. The
three sources are connected to supply voltages, U
1,2,U2,3, and
U
3,1. The SIKOSTART controller is connected inside of the delta
in series with the motor winding.
As can be seen, the source or line current is split between two
motor windings. The winding current and SIKOSTART current is
therefore less than the source or line current. Note that the
magnitude of a line current is greater than the magnitude of a
winding and SIKOSTART current by a factor of the square-root-
of-three (1.73). This allows the SIKOSTART controller to operate
a motor of a higher current rating when connected inside of the
delta.
Figure 3 - Three-phase Wye-connected Arrangement
Siemens Energy & Automation, Inc.
7
Figure 4 - Three-phase Delta-connected Arrangement
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