78 Practical examples
Entering start-up data and torque settings
Calculating/setting the motor nominal torque
You need
• the DFIG data sheets from the generator supplier for the DFIG of the wind turbine that
contain
• rated (nominal) values
• DFIG equivalent circuit (from stator side, in star connection)
• calculated operation points and type test data (optional)
• calculation tool, like Excel or calculator.
If the equivalent circuit is given in rotor-side, convert the values to stator-side.
If the equivalent circuit is in delta connection or given for main voltage, divide the
reactance and resistance values by three.
Parameters 99.05 MOTOR NOM SPEED and 99.06 MOTOR NOM POWER contain motor
nominal speed (rpm) and power. Motor nominal torque (100%) is calculated from the
values of parameters in group 99 START-UP DATA. There is no parameter for it and there
is no other way of setting the nominal torque.
Torque set-point
Torque is limited by parameters 20.05 USER POS TORQ LIM and 20.06 USER NEG
TORQ LIM. The parameters should be set to values which are achievable with the
generator-drive current capacity combination defined in the design.
If the torque reference given by the turbine controller is too high (ie, the pull-out torque of
the generator or current capacity of the converter have been reached), the converter will
limit the torque.
In extreme cases, if the torque reference is remarkably higher than what is allowed by the
generator-drive current capacity combination, and the limitation of current by limiting
torque does not succeed, the converter will trip on overcurrent. It stops operation
immediately and the torque on the generator shaft disappears. Necessary overspeed and
safety system dynamics margins must be maintained in the system design.
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