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Menu 21
Commander SK Advanced User Guide 191
Issue Number: 9 www.controltechniques.com
The motor rated frequency and the motor rated voltage (Pr 21.09) are used to define the voltage to frequency characteristic applied to the drive (see
Pr 21.09). The motor rated frequency is also used in conjunction with the motor full load rpm to calculate the rated slip for slip compensation (see
Pr 21.08 on page 191).
The motor rated current should be set at the machine nameplate value for rated current.
This value is used in the following:
• Current limit, see Pr 21.29 on page 195
• Motor protection system, see Pr 21.16 on page 195
• Slip compensation, see Pr 21.08
• Vector mode voltage control, see Pr 21.09
• Dynamic V to f control, see Pr 5.13 on page 78
The rated full load rpm is used with the motor rated frequency and No. of motor poles to calculate the rated slip of the induction machine in Hz.
The rated slip is used to calculate the frequency adjustment required to compensate for slip from the following equation:
If slip compensation is required, Pr 5.27 must be set to On(1) and this parameter should be set to the nameplate value, which should give the correct
rpm for a hot machine.
Sometimes it will be necessary to adjust this when the drive is commissioned because the nameplate value may be inaccurate. Slip compensation will
operate correctly both below rated speed and within the field weakening region. Slip compensation is normally used to correct for the motor speed to
prevent speed variation with load. The rated load rpm can be set higher than synchronous speed to deliberately introduce speed droop. This can be
useful to aid load sharing with mechanically coupled motors.
If Pr 21.08 is set to 0 or to synchronous speed, slip compensation is disabled.
If the full load speed of the motor is above 9999rpm, slip compensation should be disabled. This is because a value above 9999 cannot be entered in
Pr 21.08.
21.06 Motor 2 motor rated frequency
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
1 111
Range 0.0 to 550 Hz
Default Eur: 50.0, USA 60.0
First motor
parameter
Pr 5.06
Update rate Background
21.07 Motor 2 motor rated current
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
12 1 111
Range 0 to RATED_CURRENT_MAX A
Default Drive rated current (Pr 11.32)
First motor
parameter
Pr 5.07
Update rate Background
21.08 Motor 2 motor rated full load rpm
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
111
Range 0 to 9999 rpm
Default Eur: 1500, USA 1800
First motor
parameter
Pr 5.08
Update rate Background
Rated slip Motor rated frequency No. of motor pole pairs Motor full load rpm 60⁄×()– Pr 21.06 Pr 21.11 2⁄()Pr 21.08 60⁄()×[]–= =
Slip compensation Rated slip Active current Rated active current⁄×=
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