Load Duty Cycles; General; Standard Load Duty Cycles - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information

1.13 Load duty cycles

1.13.1

General

In many applications, especially constant-torque applications, variable-speed drives are required to operate under
overload conditions.
Overload capacity may be required occasionally, for example, in order to
· overcome breakaway torques on starting,
· produce acceleration torques for short periods, or
· decelerate drives rapidly in emergency situations.
However, overload capacity may also be needed periodically, for example, within recurrent load duty cycles for
· shears,
· flywheel presses and servo presses,
· centrifuges,
· test bays in the automotive industry,
· amusement rides in theme parks.
For the converters and inverters to be able to produce the required overload capacity, they must not be operated to
the limit of their thermal capacity prior to and following the overload periods. For this reason, the base load current for
drives which require overload capacity must be lower than the continuously permissible thermal rated current. The
more the base load current is reduced from rated current value, the higher will be the thermal reserves for periods of
overload duty.
1.13.2

Standard load duty cycles

For SINAMICS G130 converter Chassis, SINAMICS G150 and S150 converter cabinets and SINAMICS S120 Motor
Modules SINAMICS S120 (Chassis and Cabinet Modules), the overload capability is defined by two standard load
duty cycles:
·
Load duty cycle for low overload (LO) with a base load current I
than the rated output current I
·
Load duty cycle for high overload (HO) with a base load current I
25 %) than the rated output current I
The diagrams below show the load duty cycle definitions for operation under low and high overloads.
·
The base load current I
10 s.
·
The base load current I
10 s.
The maximum possible short-term current of the load duty cycle low overload (LO) is 1.5
always slightly higher than the maximum possible short-term current of the load duty cycle high overload (HO), which
is 1.6 I for 10 s. Thus the maximum possible output current I
* H
maximum value is set in the firmware and can, therefore, not be exceeded, not even in short-term operation.
The values for the base load currents I
must therefore be taken from the relevant catalogs or the chapters on specific unit types in this engineering manual.
These short-time currents apply on the condition that the converter is operated at its base load current before and
after the period of overload on the basis of a load duty cycle duration of 300 s in each case. Another precondition is
that the converter is operated at its factory-set pulse frequency at output frequencies higher than 10 Hz.
Where the ratio ΔI between short-time current and base load current or the load duty cycle duration T or the pulse
frequencies f are different, the overload capacity must be calculated in accordance with section "Free load duty
Pulse
cycles" below.
At output frequencies below 10 Hz, the additional restrictions described in section "Power cycling capability of IGBT
modules and inverter power units" apply.
SINAMICS Engineering Manual – November 2015
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Ó Siemens AG
.
rated
.
rated
for low overload is based on a load duty cycle of 110 % for 60 s or 150 % for
L
for high overload is based on a load duty cycle of 150 % for 60 s or 160 % for
H
and I , as well as for the maximum output current I
L H
that is marginally lower (3 % to 6 %)
L
that is significantly lower (10 % to
H
of the power unit is defined by I
max
I for 10 s. This value is
* L
= 1.5 I This
* L .
max
, are unit-specific and
max