Common starting methods for soft starters

Release time:

2025-05-13

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Abstract

Common Soft Starter Starting Methods

Ramp Voltage Start:
Voltage increases linearly, without current closed-loop control, potentially causing large inrush current. Suitable for simple loads (such as lightly loaded fans).

Ramp Current Start:
Current gradually increases to the set value and remains constant, resulting in a smooth start-up process and the most widely used method. Suitable for fans and pump loads (such as water pumps).

Step Start:
Quickly reaches the preset current value, with a short start-up time, suitable for scenarios requiring rapid response. Suitable for high-speed production lines and emergency start-up equipment.

Impulse Start:
Initial stage with a short-duration high-current surge, followed by constant current start-up, used to overcome static friction in heavy-load applications. Suitable for crushers, presses, and other heavy-duty equipment.

Differences Between Soft Starters and Variable Frequency Drives (VFDs)

Functional Differences:

  • Soft Starter: Only controls the start/stop process, no speed control.
  • VFD: Can adjust motor speed, enabling continuous speed control.

Output Control:

  • Soft Starter: Only adjusts voltage, frequency remains unchanged.
  • VFD: Adjusts both voltage and frequency simultaneously.

Cost Differences:

  • Soft Starter: Lower price, simple structure.
  • VFD: Higher price, complex functionality.

Application Scenarios:

  • Soft Starter: Equipment requiring smooth acceleration during start-up and no speed control (such as water pumps).
  • VFD: Equipment requiring speed control or energy saving (such as fans, conveyors).

Core Comparison of Soft Start and Direct Start

Starting Current:

  • Direct Start: Current can reach 5-7 times the rated current, with a large impact.
  • Soft Start: Current reduced to 1.5-3 times, with a small impact.

Impact on Power Grid:

  • Direct Start: May cause a sudden drop in grid voltage, affecting other equipment.
  • Soft Start: Suppresses voltage fluctuations, reducing the burden on the power grid.

Mechanical Impact:

  • Direct Start: High impact may damage bearings and transmission systems.
  • Soft Start: Gradual acceleration, reducing mechanical wear.

Applicable Power:

  • Direct Start: Usually applicable to low-power motors ≤7.5kW.
  • Soft Start: Preferred for high-power motors >7.5kW.

Installation and Debugging Points for Soft Starters

Wiring Method:

  • Main Circuit: Power supply connected to terminals 1L1/3L2/5L3 of the soft starter, motor connected to terminals 2T1/4T2/6T3.
  • Bypass Contactor: Switches to bypass operation after start-up to reduce thyristor heat generation.

Grounding Requirements:

  • The PE grounding wire should be short and directly connected to the grounding point near the mounting plate to ensure stable functional grounding.

Parameter Settings:

  • Adjust start-up time, current limit, torque curve, and other parameters according to motor power and load type.
  • Enable overload protection, phase failure protection, and other safety functions (such as Schneider ATS48 series supports Modbus communication configuration).

Common Soft Starter Models and Functions

Schneider ATS48 Series:

  • Supports Modbus/Profibus communication, integrated thermal protection, and stall monitoring.
  • Suitable Power: 75kW (400V) to 225kW (415V).

CMC-L Series:

  • Digital control, supports multiple start-up methods (ramp, constant current, pulse).
  • Built-in electronic overload protection, suitable for chemical and metallurgical industries.

HPS2D Series:

  • Fully digital control, with self-diagnostic function, suitable for textile and petrochemical industries.

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