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4.11
Permissible speed of a synchronous motor
Requirement
Overvoltage in the converter due to driven synchronous motor
If a fault occurs, or after an OFF2 command, the load machine may continue to drive the
permanent-magnet synchronous motor. This causes the permanent-magnet synchronous
motor to charge the capacitor in the DC link of the converter. Above a certain charge, the DC link
voltage of the converter reaches an impermissibly high value. An excessively high DC link
voltage damages the converter.
• Ensure that no overvoltage occurs in the converter even when the converter is disconnected
Description
The voltage induced in the synchronous motor must not exceed the available converter output
voltage. This limits the permissible maximum speed of a synchronous motor operating at the
converter.
The permissible maximum speed is calculated using the following formula:
U
DC max
k
T
SINAMICS G220 converter
Operating Instructions, 04/2024, FW V6.2, A5E51781573B AB
CAUTION
from the power supply, e.g. by taking one of the following measures:
– Limit the maximum speed to the permissible value.
– Install an appropriately dimensioned overvoltage protection.
– Install a brake on the load machine.
– Use a backstop with pumps.
Maximum permissible DC link voltage of the converter:
•
U
= 860 V for line voltage 3 AC 380 V ... 500 V
DC max
•
U
= 410 V for line voltage 3 AC 200 V ... 240 V
DC max
Torque constant of the synchronous motor according to the motor rating plate or data sheet
4.11 Permissible speed of a synchronous motor
Application planning
75
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