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TD Series Digital Solid State Soft Starter 48 - 1250A
This feature can be used with or without the Maximum Current Limit setting.
To achieve Current Ramping with the TD, set the Ramp Profile (F010) to 0002 or
0004 (Current Ramp), and the Maximum Current Limit setting (F014) to the
desired level.
4. Current Limit Only (Current Step) starting means using the Current Limit
feature exclusively without the benefit of soft starting by ramping the voltage or
current first. This will maximize the effective application of motor torque within the
limits of the motor. In this mode, Initial Voltage / Current and Ramp Time are set
to 0, so the output current jumps to the current limit setting immediately.
Examples of when to use this mode are:
• applications with a severely limited power supply
• when starting a difficult load such as a centrifuge or deep well pump
• when the motor capacity is barely adequate without stalling or overloading.
• It is a good choice when other starting modes fail.
Since ramp times are set to 0, this mode functions in either Voltage Ramp or
Current Ramp setting.
Ramp Parameter Description
Initial Torque (Initial Voltage or Initial Current). This function sets the initial
start point of either the Voltage Ramp or Current Ramp as programmed in F010.
Every load requires at least some amount of torque to start from a standstill. It is
not efficient to begin ramping the motor from zero every time, since between zero
and the (WK
2
) break-away torque level, no work is being performed. The initial
torque level should be set to provide just enough torque to make the motor shaft
begin to rotate, enabling the softest possible start and preventing torque shock
damage to the mechanical components. Setting this function too high will not
damage the starter, but may reduce or eliminate the soft start advantages. See
Chapter 5 for initial setup procedures.
Accel Ramp Time. This Function sets the maximum allowable time for ramping
the Initial voltage or current (torque) setting to either of the following:
1) Current limit setting when the motor is still accelerating, or
2) Full output voltage if the Current Limit is set to maximum.
Increasing the Ramp Time softens the start process by lowering the slope of
increase in voltage or current. This should be set to provide the softest possible
start without stalling unless you have determined that your application has other
considerations. Applications where this setting should be shorter include
Centrifugal Pumps, because pump problems may occur as a result of insufficient
torque during acceleration through the pump curve.
Note: Ramp Time is affected by the following conditions:
1.Current Limit will extend the Ramp Time if the motor does not reach full
speed while in current limit mode.
2. The Anti-Oscillation Circuit will shorten the Ramp Time if the motor reaches
full speed before end of ramp.
Current Limit. This Function sets the maximum motor current that the starter
allows during Ramping. It is active in both the Voltage Ramp and Current Ramp
modes. As the motor begins to ramp, this feature will set a ceiling at which the
current draw will be held. Current Limit will remain in effect until one of the following
two events occur:
1) The motor reaches full speed as detected by the At-Speed detection circuit.