Eaton DS7 Series, Manual

Page: 58 / 240

2 Engineering
2.12 Loading conditions
54
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
2.12.3 Different overload current
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
LRP
) can be achieved for
5 s at 10 starts per hour (overload factor X = 3).
e
The prospective locked rotor current I
LRP
is the motor current that occurs
when the rated operating voltage is applied and the rotor is locked
(I
LRP
= X x I
e
).
Figure 35: Real (dashed) and normalized load current
55A: AC-53a: 3 -5 : 75 - 10
S
F [%]
T
x
[s]
X
I
e
[A]
F = 10/h, 1 h = 3600 s l T
x
+ t
B
+ t
P
= 360 s
T
x
+ t
B
F
=
x 100 % l
T
x
+ t
B
+ t
P
5 s + 265 s
x 100 % = 75 %
5 s + 265 s + 90 s
I
LRP
X
=
l I
LRP
=
X x I
e
= 3 x 55 A = 165 A
I
e
I
e
I
LRP
I
T
x
t
B
t
P
1 h
t
t
P
1 2 10
T
I
t
I
e
I
LRP