A digital soft start (also known as a solid state soft starter) has integrated motor protection, while other starters need to have external protection from such problems as overload, short circuit, and locked rotor.
Each line on the a solid state soft start uses two thyristors that are connected to the motor. The thyristors can rapidly switch large currents at high voltages. The six thyristors that come out of the three lines from the starter control power to the motor, though only a portion of power is supplied to the motor during start.
Since a soft starter can be programmed to ramp up to a certain voltage in a set amount of time, they have more flexibility than other types of starters, including reduced voltage autotransformer starts, which have taps that only allow for certain voltages, and part winding starters, which use split motor windings.
Solid state soft starters provide longer performance with virtually no maintenance since it does not have contacts that can burn out, and also has no armatures that can break.
Since the motor protection is included, solid state starters are typically less expensive than their counterparts.
You can program a digital soft start to reach a certain current in a given amount of time. These types of soft starts will have a number of connection types for for interacting with other devices, including ethernet, ModBus RS232.485, analog and discreet triggered input terminals.
For example, the SSW07 line of digital soft start from Weg, which is carried by TEMCo, uses a Modbus RS-232 or RS-485 module to connect to a "Fieldbus" communication network.
The SSW07 digital soft start can come with either a local man-machine interface (MMI) or a remote human machine interface (HMI). The MMI interface allow for fast programming and reliability by enabling machines to copy the SSW07 parameterization. The HMI interface can be placed in a panel door or machinery console.
It can also use KSDG2 software for parameterization, command and monitoring. It will allow for SSW07 parameters to be identified, read, written and edited.
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