5 Adjustable Frequency Drive and Motor Applications
5.1 Torque Limit, Current Limit, and
Unstable Motor Operation
Excessive loading of the adjustable frequency drive could
result in warning or tripping on torque limit, overcurrent,
or inverter time. Tripping is not a concern if the adjustable
frequency drive 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 are sometimes the result of
improperly setting specific parameters. The following
parameters are important in matching the adjustable
frequency drive to the motor for optimum operation.
These settings need careful attention.
1-03 Torque Characteristics
sets the mode in which
the adjustable frequency drive operates.
Parameters
1-20 Motor Power [kW]
to
1-29 Automatic Motor Adaptation (AMA)
match the
adjustable frequency drive to the motor and
adapt to the motor characteristics.
4-17 Torque Limit Generator Mode
and
14-25 Trip
Delay at Torque Limit
set the torque control
features of the adjustable frequency drive for the
application.
1-00 Configuration Mode
sets the adjustable frequency
drive for open-loop or closed-loop operation or torque
mode operation. In a closed-loop configuration, a feedback
signal controls the adjustable frequency drive speed. The
settings for the PID controller play a key role for stable
operation in closed-loop, as described in the Instruction
Manual. In open-loop, the adjustable frequency drive
calculates the torque requirement based on current
measurements of the motor.
1-03 Torque Characteristics
sets the adjustable frequency
drive for constant or variable torque operation. It is
imperative that the correct torque characteristic is selected,
based on the application. If the load type is constant
torque and variable torque is selected, it may be very
difficult or impossible for the adjustable frequency drive to
start the load. Consult the factory if uncertain about the
torque characteristics of an application.
Parameters
1-20 Motor Power [kW]
to
1-25 Motor Nominal
Speed
configure the adjustable frequency drive for the
connected motor. These parameters are motor power,
voltage, frequency, current, and rated motor speed.
Accurate setting of these parameters is crucial. Enter the
motor data required as listed on the motor nameplate. For
effective and efficient load control, the adjustable
frequency drive 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 adjustable frequency drive measures the
electrical characteristics of the motor and sets various
adjustable frequency drive parameters based on the
findings. Two key parameter values set by this function are
stator resistance and main reactance,
1-30 Stator Resistance
(Rs)
and
1-35 Main Reactance (Xh)
. If the motor operation is
unstable, perform AMA. AMA can only be performed on
single motor applications within the programming range
of the adjustable frequency drive. Consult the Instruction
Manual for more on this function.
1-30 Stator Resistance (Rs)
and
1-35 Main Reactance (Xh)
, as
stated, are set by the AMA function, values supplied by the
motor manufacturer, or left at the factory default values.
Never adjust these parameters to random values even if it
seems to improve operation. Such adjustments can result
in unpredictable operation under changing conditions.
4-16 Torque Limit Motor Mode
sets the limit for adjustable
frequency drive torque. The factory setting is 160% for FC
302 series and 110% for/seriesFC 102FC 202 and vary with
motor power setting. For example, an adjustable frequency
drive programmed to operate a small motor yields a
higher torque limit value than one programmed to operate
a larger size motor. It is important that this value is not set
too low for the requirements of the application. In some
cases, it is desirable to have a torque limit set at a lesser
value. This offers protection for the application in that the
adjustable frequency drive limits the torque. A higher
torque may be required at initial startup, which could
cause nuisance tripping.
Adjustable Frequency Drive ...
Service Manual
MG94A222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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Summary of Contents for VLT FC 103
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