Eaton DS7 Series, Manual

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2 Engineering
2.11 Motor connection
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
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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
μ F 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
L N
L1 L3 L2
T1 T2 T3
U1 V1 W1
W2 U2 V2
U1 V1 W1
W2 U2 V2
U1 V1 W1
W2 U2 V2