Page 8 - Catalog Softstarters PSR PSE PSTX

ABB softstarters

Why motor starting and stopping matters

1 There are some common issues associated with starting and stopping electrical
motors. Depending on requirement, different starting and stopping methods
can be used.

Direct-on-line Star-delta Softstarter
Direct-on-line starting (DOL) is the A star-delta starter reduces current and Like direct-on-line and star delta
easiest and most commonly used torque during start. The starting current starters, softstarters are used to
starting method. It is suitable for stable is about one third compared to direct- start and stop motors in full-speed
networks and mechanically stiff and on-line starting, although it also reduces applications. It eliminates common
well-dimensioned shaft systems due to the starting torque to about 25 percent. problems associated with motor starting
the high current and torque generated and stopping, including electrical
during start. surges, spikes and high inrush currents.
Star-delta is not adjustable, so if the
torque is reduced too much, the motor
DOL starting is uncontrolled, which will not start. Current peaks will happen Because it offers soft starting and
means that the motor will start with when switching from star to delta stopping, a softstarter is the optimal
maximum current and torque regardless connection. compromise between a direct-on-line
of load type. or star-delta starter and a variable
speed drive in many full-speed motor
applications.

Torque Motor current Variable speed drive
Like a softstarter, a variable speed drive (VSD)
can perform soft motor starting and stopping.
However, the VSD was designed primarily to
control motor speed, resulting in energy efficient
motor operation in variable speed applications.

Using a VSD with the sole purpose of ensuring
soft starting and stopping of full-speed motors
can therefore be considered an unnecessarily
advanced solution.

Typical torque and current curves from starting a motor using DOL, star-delta and softstarter.

1/6 1SFC132012C0201 - Rev. B | Softstarter Catalog Softstarter Catalog | 1SFC132012C0201 - Rev. B | 1/7