Danfoss Drives · DKDD.PB.551.A1.02 | 21
Extreme Conditions: How can soft starters be selected
for extreme conditions?
Soft starter ratings are based on specic operating conditions.
These generally specify start time, start current, starts per
hour, duty cycle and environmental factors such as ambient
temperature and altitude. If the soft starter will be used outside
these conditions, the rating must be revised according to the
manufacturer’s instructions.
Ratings for Danfoss soft starters are published in the
soft starter’s Operating Instructions. Alternatively,
WinStart can be used to model requirements outside the
published ratings.
Example:
Compressor (Reciprocating, start unloaded), start current limited to
3,5 x FLC, motor: 132 kW, 400 V, I
n
: 226 A, I
lr
: 7,5 x I
n
.
Mains Supply: 400 V, 50 Hz-
Minimum rated current = 226 x 3,5 = 791 A
L
max
= Motor Inductance =
= 0,434 mH=
V
(√3 x I
LR
) ω
400
(√3 x 1695) × (2 × π × 50)
L
min
=
= 5,66 μH
400 V × √2
100 A
(
1 μS
)
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