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Affinity User Guide
123
Issue Number: 5 www.controltechniques.com
Pr 5.27 Slip compensation
When a motor, being controlled in open loop mode, has load applied a characteristic of the motor is that the output speed droops in proportion to the
load applied as shown:
In order to prevent the speed droop shown above slip compensation should be enabled.
To enable slip compensation Pr
5.27
must be set to a 1 (this is the default setting), and the motor rated speed must be entered in Pr
0.45
(Pr
5.08
).
The motor rated speed parameter should be set to the synchronous speed of the motor minus the slip speed. This is normally displayed on the
motor nameplate, i.e. for a typical 18.5kW, 50Hz, 4 pole motor, the motor rated speed would be approximately 1465rpm. The synchronous speed for
a 50Hz, 4 pole motor is 1500rpm, so therefore the slip speed would be 35rpm.
If the synchronous speed is entered in Pr
0.45
, slip compensation will be disabled. If too small a value is entered in Pr
0.45
, the motor will run faster
than the demanded frequency.
The synchronous speeds for 50Hz motors with different numbers of poles are as follows:
2 pole = 3000rpm, 4 pole = 1500rpm, 6pole =1000rpm, 8 pole = 750rpm
Shaft speed
Demanded speed
Load
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