5 Frequency Converter and Motor Applications
5.1 Torque Limit, Current Limit, and
Unstable Motor Operation
Excessive loading of the frequency converter may result in
warning or tripping on torque limit, overcurrent, or
inverter time. This is not a concern if the frequency
converter is properly sized for the application and
intermittent load conditions cause anticipated operation in
torque limit or an occasional trip. However, nuisance or
unexplained occurrences may be the result of improperly
setting specific parameters. The following parameters are
important in matching the frequency converter to the
motor for optimum operation. These setting need careful
attention.
1-03 Torque Characteristics
sets the mode in which
the frequency converter will operate.
Parameters 1-20 through 1-29 match the
frequency converter to the motor and adapt to
the motor characteristics.
Parameters 4-17 and 14-25 set the torque control
features of the frequency converter for the
application.
1-00 Configuration Mode
sets the frequency converter for
open or closed loop operation or torque mode operation.
In a closed loop configuration, a feedback signal controls
the frequency converter speed. The settings for the PID
controller play a key role for stable operation in closed
loop, as described in the Operating Instructions. In open
loop, the frequency converter calculates the torque
requirement based on current measurements of the motor.
1-03 Torque Characteristics
sets the frequency converter for
constant or variable torque operation. It is imperative that
the correct torque characteristic is selected, based on the
application. If, for example, the load type is constant
torque, such as a conveyor, and variable torque is selected,
the frequency converter may have great difficulty starting
the load, if started at all. Consult the factory if uncertain
about the torque characteristics of an application.
Parameters 1-20 through 1-25 configure the frequency
converter for the connected motor. These are motor
power, voltage, frequency, current, and rated motor speed.
Accurate setting of these parameters is very important.
Enter the motor data required as listed on the motor
nameplate. For effective and efficient load control, the
frequency converter relies on this information for
calculating the output waveform in response to the
changing demands of the application.
1-29 Automatic Motor Adaptation (AMA)
activates the
automatic motor adaptation (AMA) function. When AMA is
performed, the frequency converter measures the electrical
resistance of the motor stator windings, R1. Since AMA can
not calculate R2, X1, X2, and Xm (
1-31 Rotor Resistance (Rr)
to
1-35 Main Reactance (Xh)
) they must be requested from
the motor manufacturer the optimal performance of the
drive data.
1-31 Rotor Resistance (Rr)
and
1-35 Main
Reactance (Xh)
, as stated, should be set by the values
supplied by the motor manufacturer, or left at the factory
default values.
Never adjust these parameters to random values even
though it may seem to improve operation. Such
adjustments can result in unpredictable operation under
changing conditions.
4-17 Torque Limit Generator Mode
sets the limit for
frequency converter torque. The factory setting is 160% for
FC 302 series and 110% for FC 102FC 102/202 series and
will vary with motor power setting. For example, a
frequency converter programmed to operate a smaller
rated motor will yield a higher torque limit value than the
same frequency converter programmed to operate a larger
size motor. It is important that this value not be set too
low for the requirements of the application. In some cases,
it may be desirable to have a torque limit set at a lesser
value. This offers protection for the application in that the
frequency converter will limit the torque. It may, however,
require higher torque at initial start up. Under these
circumstances, nuisance tripping may occur.
14-25 Trip Delay at Torque Limit
works in conjunction with
torque limit. This parameter selects the length of time the
frequency converter operates in torque limit prior to a trip.
The factory default value is off. This means that the
frequency converter will not trip on torque limit, but it
does not mean it will never trip from an overload
condition. Built into the frequency converter is an internal
inverter thermal protection circuit. This circuit monitors the
output load on the inverter. If the load exceeds 100% of
the continuous rating of the frequency converter, a timer is
activated. If the load remains excessive long enough, the
frequency converter will trip on inverter time. Adjustments
cannot be made to alter this circuit. Improper parameter
settings effecting load current can result in premature trips
of this type. The timer can be displayed.
Frequency Converter and Mot...
High Power Service Manual for Modular F Frame Drives
MG90K202 - VLT
®
is a registered Danfoss trademark
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