Star Delta Contactor Size Calculator
Calculate optimal contactor sizes for Star-Delta motor starters
Star Delta Contactor Size Calculator
Compliant with IEC 60947 Standards
Results:
Calculated Full Load Current (A): 0.00
Making/Breaking Capacity (A): 0.00
Size of Star Contactor (A): 0.00
Size of Main Contactor (A): 0.00
Size of Delta Contactor (A): 0.00
How to Use the Calculator
Input Motor Power & Unit
- Enter the motor's power in kW or HP.
- Select the corresponding unit (kW or HP) from the dropdown.
Enter Electrical Parameters
- Provide the system Voltage (V), Phase (Single/Three), Power Factor (PF), and motor Efficiency (%).
- These values are crucial for accurate current calculation.
Select Application Type & Calculate
- Choose the appropriate AC category (e.g., AC2, AC3) based on your motor's application.
- Click "Calculate" to get the derived Full Load Current and recommended contactor sizes.
Star Delta Contactor Sizing Fundamentals
Full Load Current Calculation
The Full Load Current (FLC) is derived from the motor's power, voltage, power factor, and efficiency. This calculated FLC is then used as the basis for sizing the contactors.
Main and Delta Contactors
The Main and Delta contactors in a star-delta starter control the winding currents. These currents are approximately 1/√3 (58%) of the line current. Therefore, these contactors are rated at 58% of the motor's full load current.
Star Contactor
The Star contactor carries the star current only during the starting phase. The current in the star winding is 1/3 (33%) of the motor's full load current. Thus, this contactor can be rated at 33% of the motor's full load current.
Key Considerations:
Contactor selection is crucial for motor protection and efficient operation. Always refer to manufacturer specifications and relevant electrical standards.
Calculation Formulas
Full Load Current (FLC) from kW:
Single Phase: FLC = (kW × 1000) / (V × PF × Eff)
Three Phase: FLC = (kW × 1000) / (√3 × V × PF × Eff)
Full Load Current (FLC) from HP:
Single Phase: FLC = (HP × 746) / (V × PF × Eff)
Three Phase: FLC = (HP × 746) / (√3 × V × PF × Eff)
Size of Main Contactor = 0.58 × FLC
Size of Delta Contactor = 0.58 × FLC
Size of Star Contactor = 0.33 × FLC
Making/Breaking Capacity = AC Category Factor × FLC
Example Calculation
Given:
Motor Power: 7.5 kW
Voltage: 400 V (Three Phase)
Power Factor: 0.85
Efficiency: 88% (0.88)
Application Type: AC3 (Factor: 10)
Step 1: Calculate Full Load Current (FLC)
FLC = (7.5 kW × 1000) / (√3 × 400 V × 0.85 × 0.88) ≈ 12.15 A
Step 2: Calculate Contactor Sizes
Making/Breaking Capacity = 10 × 12.15 A = 121.50 A
Size of Star Contactor = 0.33 × 12.15 A = 4.01 A
Size of Main Contactor = 0.58 × 12.15 A = 7.05 A
Size of Delta Contactor = 0.58 × 12.15 A = 7.05 A
Summary:
Calculated Full Load Current: 12.15 A
Making/Breaking Capacity: 121.50 A
Star Contactor: 4.01 A
Main Contactor: 7.05 A
Delta Contactor: 7.05 A
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