GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) - Manual (Page 62)

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.
par. H-43 Torque Characteristics sets the mode in which the frequency converter will operate.
Parameters P-02 through P-08 match the frequency converter to the motor and adapt to the motor characteristics.
Parameters F-41 and SP-25 set the torque control features of the frequency converter for the application.
par. H-40 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.
par. H-43 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 P-02 through P-07 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.
par. P-04 Auto Tune activates the automatic motor adaptation (auto tune) function. When auto tune is performed, the frequency converter measures the electrical
characteristics of the motor and sets various frequency converter parameters based on the findings. Two key parameter values set by this function are stator
resistance and main reactance, parameters P-30 and P-35. If unstable motor operation is experienced and auto tune has not been performed, it should be done.
auto tune can only be performed on single motor applications within the programming range of the frequency converter. Consult the Operating Instructions for
more on this function.
Parameters P-30 and P-35, as stated, should be set by the auto tune function, 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.
par. F-41 Torque Limiter (Braking) sets the limit for frequency converter torque. The factory setting is 160% for AF-650 GP series and 110% for AF-600 FP 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.
par. SP-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.
5.1.1 Overvoltage Trips
This trip occurs when the DC bus voltage reaches its DC bus alarm voltage high (see ratings tables in introductory section). Prior to the trip, the frequency converter
will display a high voltage warning. Most times an over voltage condition is due to fast deceleration ramps with respect to the inertia of the load. During deceleration
of the load, inertia of the system acts to sustain the running speed. Once the motor frequency drops below the running speed, the load begins overhauling the
AF-650 GP and AF-600 FP High Power Service Manual
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