Toshiba VF010H05 - Manual (Page 13)

JKSSS+ Series - 7
JKSSS+ Series 2.3 - 4.2KV
until one of three things happen: the motor accelerates to full speed, the Ramp
Time expires or a Current Limit setting is reached.
If the motor accelerates to full speed before the ramp time setting has expired,
an automatic Anti-Oscillation feature will override the remaining ramp time and
full voltage will be applied. This will prevent any surging or pulsation in the mo-
tor torque, which might otherwise occur due to the load not being fully coupled
to the motor when operating at reduced voltage and torque levels.
If the motor has not reached full speed at the end of the ramp time setting,
the current limit setting will proportionally control the maximum output torque.
Feedback sensors in the JKSSS+ Series provide protection from a stall condi-
tion, an overload condition or excessive acceleration time.
The Current Limit feature is provided to accommodate installations where there
is limited power available (for example, on-site generator power or utility lines
with limited capacity). The torque is increased until the motor current reaches
the preset Current Limit point and it is then held at that level. Current Limit
overrides the ramp time setting so if the motor has not accelerated to full speed
under the Current Limit setting, the current remains limited for as long as it
takes the motor to accelerate to full speed.
When the motor reaches full speed and the current drops to running levels, the
soft starter detects an At-Speed condition and closes the Bypass Contactor.
The Bypass Contactor serves to shunt power around the SCR stack assemblies
to prevent heat buildup in the starter enclosure due to the slight voltage drop
across the SCRs. At this point, the soft starter has the motor operating at full
voltage, just as any other starter would.
Other starting methods available in the soft starter are:
· Current Ramp: Uses a closed current feedback PID loop to provide a linear
torque increase up to a Maximum Current level.
· Constant Current: Current is immediately increased to the Current Limit
point and held there until the motor reaches full speed.
· Custom Curve: Gives the user the ability to plot torque and time points on a
graph. The soft starter will then accelerate the motor following these points.
· Tachometer Feedback Ramp: Uses a closed loop speed follower method
monitoring a tachometer input signal from the motor or load shaft.
Deceleration: The soft starter provides the user with the option of having
the load coast to a stop or controlling the deceleration by slowly reducing the
voltage to the motor upon initiating a stop command. The Decel feature is the
opposite of DC injection braking in that the motor will actually take longer
to come to a stop than if allowed to coast to a stop. The most common ap-
plication for the Decel feature is pumping applications where a controlled stop
prevents water hammer and mechanical damage to the system.