Section Five - Danfoss VLT Series Service Manual

APPLICATIONS
CURRENT LIMIT TRIPS
UNSTABLE MOTOR
OPERATION
Excessive loading of the VLT may result in "CURRENT LIMIT" trips. This is not a
concern if the unit has been properly sized and intermittent load conditions cause
anticipated operation in current limit. Nuisance current limiting and unstable motor
operation can, however, be caused by improperly setting specific parameters.
The following parameters are those which are most critical to the VLT/Motor
relationship.
100 - Load Type
103 - Motor Power
104 - Motor Voltage
105 - Motor Frequency
107 - Motor Current
108 - Motor Magnetizing Current
109 - Start Voltage
110 - Start Compensation (VLT 3000 only)
209 - Current Limit
PARAMETER 100
Load type is selected based on application demands. VLT Series 3000 drive can
be set for both constant and variable torque applications. The VLT Series 3500
drive is specifically designed for variable torque applications. The available
selections vary between these different series. An incorrect setting may provide
an improper voltage to frequency (V/F) ratio to the motor with respect to load
demand. For example, a constant torque (CT) load requires a higher V/F ratio at
start-up than a variable torque (VT) load. If a VT mode of operation has been
selected for a CT load, sufficient starting torque will not be available.
When a VLT Series 3000 unit is set for one of the variable torque modes,
adjustments to parameters 109-113 will have no effect. The various VT modes
have direct control over these parameters. When one of the CT Start/VT modes is
selected on a VLT Series 3000 unit, the above mentioned parameters will have
effect only until the reference has been reached. At this point the unit reverts to VT
operation. It should be noted that parameters 110-113 do not exist in the VLT
Series 3500.
PARAMETERS 103, 104, 105, 107
These parameters, when incorrectly set, have an effect on other parameters as
well as the unit's interpretation of the load. In setting these parameters enter the
name plate data from the motor into the appropriate parameter. Use the conversion
chart to change from HP to KW.
HP 1 2 3 5
kW 0.75 1.5 2.2 4.0
HP 100 125 150 200
kW 75 90 110 160

Section Five

7 10 15 20 30 40
5.5 7.5 11 15 22 30
250 300
185 200
50 60 75
37 45 55
5 - 1