Eaton DS7 - Connection of AC Motors

2 Engineering
2.11 Motor connection
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com 45
2.11.5 Connection of AC motors
AC motors can also be operated with the DS7 soft starters series. Only the
version of the three-phase asynchronous motor with a capacitor (Steinmetz
circuit) is considered suitable for industrial use.
In practice, single-phase motors up to an output of around 2.2 kW (230 V) are
used. In the Steinmetz circuit, metal paper capacitors (450 V) with around 60
to 80 μF per kilowatt motor output are required (DIN 48501).
When connected to a single-phase AC supply, they form an auxiliary phase
with a phase shift of around 90°. Compared to the required phase shift of
120° this causes an elliptical rotating field. As a result, the starting torque
(M
A
) is reduced to around 30 % of the rated-load torque (M
N
). If a higher
starting torque is required (90 - 100 %), additional starting capacitors must be
used which are only switched for the startup phase, in parallel to the
operation capacitor. During operation, the torque is around 70 % of the
normal motor output.
Delta circuit
Star connection
Semi star circuit
Figure 28: Permissible motor connection circuits when connecting to a single-phase AC supply
system
LN
L1 L3L2
T1 T2
T3
U1 V1 W1
W2 U2 V2
U1 V1 W1
W2 U2 V2
U1 V1 W1
W2 U2 V2