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

Fundamental Principles and System Description
Engineering Information
█

Load duty cycles

General

In many applications, especially constant-torque applications, variable-speed drives are required to operate under
overload for brief periods, e.g. in order
•
to overcome breakaway torques on starting,
•
to produce acceleration torques for short periods,
•
to shut down drives rapidly in emergency situations.
For the converters and inverters to be able to produce this overload capacity for brief periods, they must not reach
the limits of their thermal capacity in normal operation. For this reason, the base-load current for drives with overload
capacity must be lower than the continuously permissible rated current. The more the base load current is reduced
from rated current value, the higher will be the thermal reserves for brief periods of overload duty.

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
for 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 owerload (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 overload values apply on the condition that the converter is operated with the default pulse frequency 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.
Definition of the standard load duty cycle low overload
SINAMICS Engineering Manual – May 2008
98/396
© Siemens AG
.
rated
.
rated
for low overload is based on a load duty cycle of 110 % for 60 s or 150 % for
L
for a high overload is based on a load duty cycle of 150 % for 60 s or 160 %
H
and I , as well as for the maximum output current I
L H
Definition of the standard load duty cycle high overload
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