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2 Engineering
2.12 Loading conditions
2.12.3 Different overload current
54
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
If load cycles or start frequencies are different, the following graphs can be
used for reading the possible time current combination.
The example shown here is a 30 kW motor (400 V, 55 A) with an assigned
DS7-34xSX055... soft starter (55 A, rated operational current = motor
current). The maximum starting current of 165 A (I
5 s at 10 starts per hour (overload factor X = 3).
55A: AC-53a: 3 -5 : 75 - 10
I
1
I
LRP
I
e
t
t
T
B
P
x
e
F = 10/h,
1 h = 3600 s l T
T
+ t
x
B
F
x 100 % l
=
T
+ t
+ t
x
B
P
5 s + 265 s
x 100 % = 75 %
5 s + 265 s + 90 s
I
LRP
X
l I
X x I
=
=
LRP
e
I
e
The prospective locked rotor current I
when the rated operating voltage is applied and the rotor is locked
(I
= X x I
).
LRP
e
I
I
LRP
I
e
T
Figure 35: Real (dashed) and normalized load current
S
F [%]
T
[s]
x
X
I
[A]
e
2
10
1 h
+ t
+ t
= 360 s
x
B
P
= 3 x 55 A = 165 A
LRP
) can be achieved for
LRP
t
t
P
is the motor current that occurs
t
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