ABB PSTX250 - Voltage ramp

76 Functions | Installation and commissioning manual | 1SFC132081M0201
7.2 Voltage ramp
When using the Voltage ramp, the voltage increases
linearly from Initial start level to full voltage during start,
and decreases linearly from the Step down level to Stop
end voltage level during stop, see Figure 7.1.
The torque not always follows the voltage curve, because
the torque is also subject to the current. This has the
effect that the torque does not increase or decrease
linearly.
7.2.1 Voltage start ramp
When the Softstarter receives a start signal, the
Softstarter quickly increases the voltage to the Start
ramp initial level. The Softstarter then controls the output
voltage in a start ramp.
When the output voltage comes at Top of ramp, the
Softstarter closes the bypass, see Figure 7.2.
To come at Top of ramp these conditions are necessary:
• The Start ramp time passed, i.e. 100% output voltage.
• The current is below 1.2 × nominal motor current.
The Start ramp time is the time it takes to go from Start
ramp initial level to full voltage. The time to come at Top
of ramp can be longer than the set Voltage ramp time,
because this is subject to the current.
If the motor starts with a very heavy load, the start ramp
time can be longer than usual.
Example: If the Start ramp time is set to 2 seconds and
the motor starts a heavy load, this can cause the output
current to not go below the set 120% of nominal motor
current when the pre-set start ramp time is reached.
Configuration of the Voltage start ramp with these
parameters:
Parameter Description Setting range Default value
02.01 Start mode Set the Start mode to Voltage ramp. Voltage ramp,
Torque ramp,
Full voltage ramp
Voltage ramp
02.03 Start ramp Initial level Set the voltage level from where the start ramp initiates 10 ... 99% 30%
02.04 Start ramp time Set the effective time it takes for the voltage to reach
100%.
1 ... 120 s 10 s
Figure 7.1
Start and stop ramp
1SFC132081M0201
U
TimeStart ramp Stop ramp
Figure 7.2
Voltage start ramp
U
Time
Start ramp time
Start ramp initial level
Top of ramp
Nominal voltage 100 %
1SFC132081M0201
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