Siemens SINAMICS G130 Engineering Manual page 316

Drive Dimensioning
Engineering Information
Protection measures in the field-weakening range
In order that the maximum permissible DC link voltage is not exceeded and the DC link capacitors are not damaged
in the event of a trip of the converter during operation in the field-weakening range, either the motor speed must be
limited, or other suitable measures must be taken to ensure that the maximum permissible DC link voltage is not
exceeded, e.g. by the use of a appropriate dimensioned Braking Module.
1. Limitation of the speed in the field-weakening range
With SINAMICS G130, G150, S120 (Chassis and Cabinet Modules) and S150 operating in vector control mode, the
speed in the field-weakening range is limited to the value n
Key to abbreviations:
•
n Maximum permissible speed in the field-weakening range for the protection of the converter
max
•
n Rated motor speed
Rated
•
I Rated motor current
Rated
•
P Rated motor output power
Rated
•
U Maximum permissible DC link voltage of the converter or inverter in dependency on the
DC max
line supply voltage:
- 820 V for units with a line supply voltage of 380 V – 480 V 3AC
- 1022 V for units with a line supply voltage of 500 V – 600 V 3AC
- 1220 V for units with a line supply voltage of 660 V – 690 V 3AC
With synchronous motors of the series HT-direct 1FW4, the maximum permissible field-weakening speed is limited to
1.2 times the rated speed. Thus it lies within the limit defined in the given formula. With synchronous motors of other
manufacturers, often much higher field-weakening speeds are permissible.
2. Use of a Braking Module
Until the introduction of firmware version V2.4 the maximum permissible speed n
formula was not changeable by means of parameterization. Since the introduction of firmware version V2.5, it is
possible to increase the limit speed. However, the essential requirement for this is, that the drive is equipped with an
appropriate dimensioned Braking Module in order to limit the DC link voltage in the event of a trip of the drive. With
the implementation of this measure, field-weakening speeds up to 2.5 times faster than the rated speed can be
achieved.
Protection concept
Since permanent-magnet synchronous motors with a rotating rotor are an active voltage source generating a voltage
in proportion to the speed, it is not safe simply to disconnect the converter from the supply system and wait for the
DC link to discharge before starting with maintenance or repair work. Additional measures must be taken to ensure
that the rotating synchronous motor is not generating any voltage at the converter output. This can be achieved either
by blocking the motor mechanically or, in cases where the type of application means that rotary movement of the
motor cannot be completely precluded, by disconnecting the converter from the motor by a switch at the output side
of the converter.
It is generally not safe to perform any maintenance or repair work on the motor terminal box or the motor cable, until
measures have been taken to preclude any risk of rotor movement, the supplying converter is reliably disconnected
from the supply system and the converter DC link is discharged.
SINAMICS Engineering Manual – May 2008
316/396
© Siemens AG
max
V
3
= ⋅ ⋅
DC max
n n
max Rated
2 P
by factory settings, in order to protect the converter.
⋅
I
Rated
.
Rated
according to the above given
max