SIEMENS
SINAMICS S150 NEMA
Engineering Information
3
Siemens D21.7
(Part 2) – 2015
3/5
Motor and drive sizing, overloads
Dimensioning of drives
The SINAMICS S150 drive may be operated with both
variable torque and constant torque loads at either low or
high overload duties.
For variable torque (VT) loads (torque is proportional to
the square of the speed) such as fans/blowers, centrifugal
pumps and compressors, the rated continuous output
current of the drive should be at least equal to the motor
current at full torque at the required load point.
It is recommended that the rated continuous output current
of the drive be equal to or larger than the motor FLA (full
load amps) when fully utilized (SF = 1.0).
For constant torque (CT) loads, the drive base load current
(for either low or high overload duty, as required by the
application) should be at least equal to the motor current at
full torque at the required load point.
Motor and drive sizing
Service Factor must be considered for motors operating
at Service Factors beyond 1.0. Please consult factory for
assistance sizing the drive.
Motor rated current greater than drive rated current:
If the rated current (FLA) of the selected motor is larger
than the rated drive output current, the motor can only
be operated at partial load. The following limit must
be observed:
The maximum drive output current (overload current)
should be greater than or equal to the rated current
(FLA) of the motor. If this dimensioning instruction is not
observed, current peaks can occur as a result of the low
leakage inductance of larger motors, which can either lead
to nuisance tripping or can cause a continuous reduction in
output by the drive’s internal protection circuit.
Rated motor current much smaller than drive rated current:
In sensorless vector control, the rated motor current (FLA)
must be at least 1⁄4 of the rated drive output current.
With lower motor currents, operation is possible in Volts/Hz
control mode only.
Overload capability
SINAMICS S150 drives may be operated at either low or
high overload duties. The drives have an overload reserve
to deal with breakaway torques, for example. If larger
surge loads occur, this must be taken into account when
configuring. In drives with overload requirements, the
appropriate base load current must therefore be used as
a basis for the required load.
The criterion for overload is that the drive is operated with
its base load current before and after the overload occurs,
and a duty cycle duration of 300 s is assumed.
The base load current I
L
for a low overload is based on a duty
cycle of 110% for 60 s or 150% for 10 s.
The base load current I
H
for a high overload is based on a
duty cycle of 150% for 60 s or 160% for 10 s.
Low overload
High overload