10 • Introduction
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Figure 1- HRVS-DN Cabinet Type IP31 (NEMA1)
Figure 2- HRVS-DN Chassis Type (IP00)
3.2 How Soft Starters Work?
By using thyristors (SCRs) in a phase angle control mode, reduced voltage control can be achieved. Phase
control makes it possible to gradually increase the motor terminal voltage from an initial set point up to the
system supply voltage level. The related starting current and the starting torque can be optimally adjusted to
the motor/load conditions.
Figure 5
shows a principal voltage increase curve.
Figure 6
demonstrates the torque reduction compared to the DOL torque. Figure 7 demonstrates typical
behavior of motor current.
Figure 5 – Voltage Increase
Figure 6 – Torque Reduction
Figure 7 – Current Limit
In addition, the Solcon HRVS-DN soft starters provide the "soft stopping" function as a standard feature.
Similar to the reduced voltage start, a stop command gradually reduces the motor voltage over time until the
motor stops. Abrupt stopping is avoided, a specific advantage in pumping applications to prevent the
damaging effects of water hammer and on conveyor belts where the load may be damaged by an abrupt stop.
Figure 3 - Principle Diagram of Digital Medium Voltage Soft
Starter (Bypass Preparations not Shown)
Figure 4 - Phase Control of the Line Voltage Using
Semiconductor (SCR) Elements
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