Precise Selection and Supporting Solutions for Soft Starters/Variable Frequency Drives

Precise Selection and Supporting Solutions for Soft Starters/Variable Frequency Drives for Four Core Scenarios (Water Pumps/Fans/Compressors/Machine Tools)

All solutions below are centered on Schneider’s mainstream models (adapted to the mainstream demands of industrial sites), organized by scenario-based selection logic + core equipment models + main/control circuit supporting components + scenario-specific notes. All specifications are ready-to-implement and can be directly used for equipment procurement and electrical cabinet fabrication.

1. Water Pump Scenario (Industrial Water Supply/Water Supply and Drainage/Circulating Pumps)

Core Selection Logic

– For constant-speed water supply/only shock prevention during start-stop (예를 들어, municipal constant-pressure make-up water pumps, cooling tower circulating pumps): Select a soft starter to solve the problems of starting current impact and pipeline water hammer effect at a low cost;

– For constant-pressure water supply/water pressure adjustment on demand (예를 들어, secondary water supply in residential quarters, industrial variable-frequency water supply): Select a variable frequency drive (VFD) to realize closed-loop water pressure regulation, save 20%-50% energy, and avoid overpressure/undervoltage of the pipe network.

Recommended Mainstream Models

Complete Supporting Solutions (Taking a 55kW Water Pump as an Example)

Constant Speed (Soft Starter Solution)

Main circuit: TeSys GV3 Circuit Breaker (GV3ME80) → ATS480C11Y Soft Starter → TeSys LC1D Contactor (LC1D80M7C, for bypass) → Motor

Control circuit: RXM Miniature Relay (RXM2LB2BD) + Liquid Level Transducer/Pressure Switch + Surge Protector (PRD10r)

Constant Pressure (VFD Solution)

Main circuit: TeSys GV3 Circuit Breaker (GV3ME80) → ATV610U55N4 VFD → Motor

Control circuit: Pressure Transmitter (XMLP060D2101, 4-20엄마) + PLC (TM3 Series) + Surge Protector (PRD20r)

Scenario-Specific Notes

1. When a soft starter is selected for water pumps, enable the soft stop function (stop time: 5-10s) to completely eliminate water hammer;
2. VFDs for constant-pressure water supply must be configured with the PID regulation function and bound to a pressure transmitter to realize automatic closed-loop water pressure control;
3. For submersible pumps, enable the submersible pump protection function in the VFD to prevent dry running of the motor due to lack of liquid.
4. Fan Scenario (Axial Fans/Centrifugal Fans/Boiler Induced Draft Fans)

Core Selection Logic

For constant-speed operation (예를 들어, boiler induced draft fans, plant exhaust fans, cooling tower fans): Select a soft starter to solve the wind resistance impact during fan startup and avoid power grid fluctuations;

For air volume adjustment on demand (예를 들어, central air conditioning fans, blast furnace blast fans, environmental dust removal fans): Select a VFD to adjust speed based on temperature/pressure/flow signals, 절약 30%-60% energy (fan load is proportional to the cube of speed, making speed regulation the most effective energy-saving method).

Recommended Mainstream Models

Complete Supporting Solutions (Taking a 75kW Boiler Fan as an Example)

Constant Speed (Soft Starter Solution)

Main circuit: TeSys GV7 Circuit Breaker (GV7RE100) → ATS480C14Y Soft Starter → TeSys LC1D115M7C (Bypass Contactor) → Motor

Control circuit: Temperature Transducer (PT100) + Intermediate Relay + Surge Protector (PRD10r)

Air Volume Adjustment (VFD Solution)

Main circuit: TeSys GV7 Circuit Breaker (GV7RE100) → ATV610U75N4 VFD → Motor

Control circuit: Flow Transmitter (4-20엄마) + Siemens PLC S7-200SMART + Braking Unit (VW3A7801, for fan deceleration braking)

Scenario-Specific Notes

1. Fans are light-load startup equipment; soft starters/VFDs can be selected according to the rated current of the motor without derating;
2. For variable-frequency air volume adjustment, set a minimum speed limit (generally ≥30Hz) to prevent fan surge/stall;
3. High-temperature resistant supporting components must be selected for boiler induced draft fans, and the VFD cabinet shall be heat-insulated.

III. Compressor Scenario (Screw/Piston/Scroll Air Compressors)

Core Selection Logic

Compressors are heavy-load startup equipment (with high static friction of the rotor during startup), so soft starters are the first choice (operation at rated mains frequency, adapted to the loading/unloading working mode of air compressors);

Only for variable-frequency constant-pressure air supply (예를 들어, continuous air supply in precision chemical/electronic workshops): Select a heavy-duty (HD) VFD to realize pressure closed-loop control and save 15%-30% energy (avoid energy loss caused by frequent loading/unloading of air compressors).

> Key Note: Ordinary light-load VFDs are strictly prohibited for air compressors; heavy-duty (HD) models must be selected to adapt to the high torque requirements during startup/loading.

Recommended Mainstream Models

Complete Supporting Solutions (Taking a 110kW Screw Air Compressor as an Example)

Constant Speed (Heavy-Duty Soft Starter Solution)

Main circuit: TeSys GV7 Circuit Breaker (GV7RE160) → ATS480C21Y Soft Starter → TeSys LC1D150M7C (Bypass Contactor) → Motor

Control circuit: Pressure Switch (XMLA010A2S11) + Air Compressor Special Controller + Thermal Overload Relay (LR9F7375)

Variable-Frequency Constant Pressure (Heavy-Duty VFD Solution)

Main circuit: TeSys GV7 Circuit Breaker (GV7RE160) → ATV610HD11N4 VFD → Motor

Control circuit: Pressure Transmitter (XMLP010D2101) + PID Regulation Module + Braking Resistor (VW3A1107)

Scenario-Specific Notes

1. Soft starters for air compressors must be selected according to 1.25 times the rated motor current, and the current-limited startup function (current limit: 3 정격 전류의 배) shall be enabled to adapt to heavy-load startup;
2. Variable-frequency air compressors must be bound to the air tank pressure signal, and loading/unloading delay shall be set to avoid frequent speed regulation of the VFD;
3. For piston air compressors, add a travel switch to the control circuit to realize the linkage between the motor and piston movement.
4. Machine Tool Scenario (Lathes/Milling Machines/Machining Centers: Spindles/Feed Axes)

Core Selection Logic

Machine tools are high-precision speed regulation equipment, and VFDs are the only choice for the entire operation process (soft starters have no speed regulation function and are completely inapplicable). Select the corresponding VFD according to the precision requirements of spindles/feed axes, with core requirements of high speed regulation accuracy, fast response speed and high low-frequency torque.

– For ordinary lathes/milling machines (spindles/feed axes): Select general high-precision VFDs;

– For machining centers/CNC lathes (servo-level feed axes/spindles): Select machine tool-specific VFDs (or servo drives directly).

Recommended Mainstream Models

Complete Supporting Solutions (Taking a 7.5kW CNC Lathe Spindle as an Example)

Main circuit: TeSys GV2 Circuit Breaker (GV2ME20) → ATV340U07N4 VFD → Machine Tool Spindle Motor

Control circuit: CNC System (Fanuc/Siemens) + Encoder (E6B2-CWZ6C, for closed-loop speed measurement) + Intermediate Relay (RXM4LB2BD) + Emergency Stop Switch

Scenario-Specific Notes

1. For machine tool VFDs, enable the closed-loop vector control (equipped with an encoder) to realize precise speed following and avoid machining accuracy deviation of workpieces;
2. For feed axis VFDs, set the jog function (low speed: 0.5헤르츠) to adapt to manual fine adjustment of machine tools;
3. For machining centers, select anti-interference VFDs and perform grounding/shielding treatment to prevent the VFD from interfering with the CNC system.

General Supporting Selection Principles (Applicable to All Scenarios)

1. Main circuit circuit breaker: The rated current is 1.1-1.2 times the rated current of the soft starter/VFD; select molded case/miniature circuit breakers according to the power;
2. Bypass contactor (for soft starters only): The rated current is consistent with that of the soft starter; select AC contactors (AC220V/380V coil);
3. Protection components: Surge protectors (PRD Series) are mandatory to prevent power grid surges; add reactors (VW3A7501) for high-power equipment to suppress harmonics;
4. Control circuit: Prioritize 4-20mA analog signals for transducers/transmitters to adapt to the analog input ports of VFDs/PLCs.