Technical data and characteristic curves
6.1 Explanations
S-1FT7 synchronous motors
Configuration Manual, 09/2018, A5E45099423B AA
133
Speed limits n
max mech
and n
max conv
The speed range is limited by the following variables:
● The mechanical speed limit n
max mech
(rotor centrifugal forces, bearing lifetime)
● The electrical speed limit n
max conv
(voltage strength of the converter and/or max.
frequency of the converter)
It is not permissible that the maximum permissible speed n
max
exceeds the mechanical
speed limit n
max mech
nor the electrical speed limit n
max conv
.
Damage to the converter due to excessively high speeds
A motor speed greater than n
max conv
can induce a voltage in the winding, which is higher
than the permissible voltage at the converter. This induced voltage can destroy the
converter.
• Run the motor at speeds n
max conv
.
Torque limit when operating on a SINAMICS S120 drive system with field weakening
The field weakening function is active as standard on the SINAMICS S120 drive system.
A field-weakening current is injected in such a way as to enable operation to the right of or
above the voltage limiting characteristic.
In the diagram "Torque characteristics of synchronous motors" below, the area with field
weakening is marked with "B".
The shape of the voltage limiting characteristic for field weakening is determined by the
winding version (armature circuit) and the magnitude of the converter output voltage.
The voltage limiting characteristic is calculated for a motor at operating temperature.
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