What Is a Soft Starter?

Why Is a Soft Starter Needed?

When an electric motor starts directly across the line (DOL starting), it typically draws a very high starting current—often 5 to 8 times its rated current. This sudden surge can cause several problems:

• Voltage drops in the Power Supply network

• Excessive mechanical stress on motor shafts, couplings, and driven equipment

• Increased wear and tear, leading to shorter equipment lifespan

• Higher risk of electrical and mechanical failures

A Soft Starter addresses these issues by limiting the starting current and torque, allowing the motor to ramp up smoothly to its rated speed.

Key Features of a Sosiat Soft Starter

Modern Soft Starters typically offer the following features:

• Soft start: Limits inrush current and starting torque

• Soft Stop: Prevents water hammer in pumps and mechanical shock in driven loads

• Current and Voltage Control

• Motor protection functions such as:

  • Overload protection

  • Phase loss protection

  • Phase imbalance protection

  • Under-voltage and over-voltage protection

• Adjustable parameters for different load types