GE Industrial Solutions ASTAT XT - Manual (Page 7)

7 • Generalities
1.
GENERALITIES
1.1 Squirrel-Cage Motor Starting
There are numerous applications where soft starting and limited current peak are needed, thereby making direct
starting of squirrel-cage motors impossible. Traditionally in such cases other types of starting with reduced stator
voltage have been resorted to. The best-known are star-delta starters, autotransformer starters, stator resistance
starters or using part winding motors.
Any reduced starting voltage imposes a current limitation, thus reducing the starting torque, but there will always
be peaks during the change from one point or state to another which can damage the machine being driven.
Note that in general, all reduced voltage starts reduce torque in squared proportion to the current in the phases of
the motor (not on the line) and the latter in turn is reduced in linear proportion to the voltage. From this it can be
deduced that any start with reduced voltage reduces the torque in squared proportion to the voltage per motor
phase. From this point of view soft starting produces just like any other reduced voltage start, a reduction in starting
torque, according to the adjusted parameters. The advantage is the ease with which this ramp can be controlled to
produce a soft start in accordance with the actual requirement of the machine.
1.2
Advantages of the ASTAT-XT Solid State Soft Starters
Increase in productivity and reliability with the use of static soft
starters
Starting and stopping the motor without steps or transitions lengthens the life
of power-driven machine mechanical elements, greatly reducing stress on
transmission and coupling parts.
Consequently, overhauling times are reduced and machine and facility
lifespans are lengthened.
Improvement in acceleration / deceleration characteristics
Being able to start by using the voltage ramp or alternatively by limiting
current lets acceleration fit the load characteristics. Application of a pulse
start may also be selected in cases of high static friction load.
Stopping may be made by cutting-off power or by soft stop ramp.
Protected motor
The soft starter protects the motor from overloads as well as from incorrect
operating conditions such as loss of an input or output phase, blocked rotor,
thyristor short circuit, etc.
Digital technology
The control system is based on the use of a highly specialized microcontroller
by which signals are treated digitally, thereby avoiding deratings and
adjustments common to analogue circuits and obtaining excellent precision
and speed of execution.
The control board is made with the technology of surface mounting devices
(SMD), which increases equipment reliability.
High level of immunity
Design of the unit was closely tied to the conditions of supply lines, which
handle more disturbances every day. The control signals are
opto-electronically isolated and various levels of protection have been set up
in the circuits to immunize the equipment against external disturbance and its
effects.
Easy to run and adjust
This unit can be used for a wide range of applications.
Adjustments are very easy to make and diverse options maybe selected for
have equipment capabilities suited to application needs every time.
Easy maintenance due to full monitoring
The alphanumeric display and the LEDs on its front overlay makes the
equipment working conditions known at any time.
Pump control
The ASTAT-XT includes several soft stop curves which is more effective than
the standard soft stop, reducing fluid surges or hammering in a pipe line
system. This method reduces the motor speed, by controlling internal
parameters in the motor as well as the output voltage in a close-loop system.
Advanced functions
The ASTAT-XT includes advanced functions, like linear acceleration ramp,
forward and reverse jog, programmable I/O or connection to a control system
via Modbus protocol included as standard and other optional protocols.
These functions allow the incorporation of the soft starter to a distributed
control net, in automated plant processes, together with other soft starters,
programmable controllers, variable speed drives, etc.