Eaton DS7 Series, Manual

Page: 57 / 240

2 Engineering
2.12 Loading conditions
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
53
2.12 Loading conditions
DS7 soft starters are designed for a standard duty cycle as defined for
AC-53a in product standard IEC/EN 60947-2-1. This means:
3-fold overcurrent for 5 seconds with a duty factor of 75 % and 10 starts
per hour. For example: 4A: AC-53a: 3-5: 75-10
With applications such as water pumps (circulating pumps) the DS7 soft
starter with the assigned rated operational current can be selected. When
different operating frequencies, acceleration and/or starting currents are
involved, the thermal capacity of the DS7 soft starter must be taken into
account in the design.
2.12.1 Overload capability (load to AC-53a)
The table below shows the overload capability of the soft starter in
accordance with the product standard IEC/EN 60 947-4-2. It shows:
X = Value of basic overcurrent in multiples of the rated device current
T
x
= Duration of the overcurrent X in seconds
F = Duty factor within the load cycle in %
S = Number of permissible starts per hour
2.12.2 Conversion of the overload capability to lower overcurrents
The stated cycle can be converted for lower overcurrents, but not for higher!
The following formula is used to calculate the new time:
T
xnew
= New permissible time for the new overcurrent X
new
X
new
= Required overcurrent (must be less than the stated values)
Example
For X = 3, T
x
= 5 s: With a reduced overcurrent (X = 2.5) a new permissible
overcurrent duration T
xnew
of 7.2 seconds is calculated.
￫
The appendix ( ￫ page 219) contains overload curves for various
time, current, and starts-per-hour combinations that can be used
to select the right DS7 soft starter for your application.
Overcurrent X [
x
] Overcurrent time T
x
[s]
Duty factor F [%] Starts per hour S
DS7-34… 3 5 75 10
T
xnew
=
X
2
x T
x
X
2
new
T
xnew
=
3
2
x
5 s
= 7.2 s
2.5
2
￫
The parameters X x I
e
, T and the number of starts allow any
number of combinations of this load cycle with the same
thermal load.