Star Delta Starter Component Calculator
Calculate components for three-phase Star Delta starters
Star Delta Starter Calculator
For Three Phase Motor Applications
Results:
Other Materials:
- ON Push Button:
- OFF Push Button:
- Timer:
- Control Circuit Breaker:
- Control Circuit Wire:
How to Use the Calculator
Input Motor Details
- Enter the motor's power in Kilowatts (kW).
- Input the system's line-to-line Voltage (V).
- Provide the motor's Power Factor (PF) (typically between 0.7 and 0.9).
Understand Outputs
- View the calculated Full Load Current (FLC).
- See recommended Circuit Breaker sizes for Instantaneous and Inverse Trip.
- Check current flow and size for Main, Delta, and Star contactors.
- Find Thermal Overload Relay ratings and set values.
Additional Components
- Note the required control circuit wire size.
- Identify the number of ON/OFF push buttons.
- See the specification for the control circuit breaker.
- Confirm the need for a timer in the control circuit.
Star Delta Starter Fundamentals
Purpose
Star Delta starters are used to reduce the starting current of three-phase induction motors, protecting the motor and the power supply from high inrush currents during startup.
Operation
- Motor starts in Star (Y) connection, reducing voltage and current.
- After a set time, it switches to Delta (Δ) connection for full voltage operation.
Key Formulas:
Motor FLC (Three Phase): I = (kW × 1000) / (√3 × V × PF)
Main/Delta Contactor Current: 0.58 × FLC
Star Contactor Current: 0.33 × FLC
Calculation Formulas
Motor Full Load Current (FLC):
FLC = (kW × 1000) / (1.732 × Voltage × Power Factor)
Circuit Breaker Size (Instantaneous Trip):
800% of Motor FLC
Circuit Breaker Size (Inverse Trip):
250% of Motor FLC
Current Flow from Main Contactor:
58% of Motor FLC
Current Flow from Delta Contactor:
58% of Motor FLC
Current Flow from Star Contactor:
33% of Motor FLC
Contactor Size (AC7b):
125% of respective Contactor Current
Contactor Making/Breaking Capacity:
8 × respective Contactor Current
Thermal Overload Relay Rating/Set Value:
125% of Delta/Main Contactor Current (Rating)
Equal to Delta/Main Contactor Current (Set Value)
Example Calculation
For a 30 kW, 400V, 0.8 PF Three Phase Motor:
1. Motor FLC:
FLC = (30 × 1000) / (1.732 × 400 × 0.8) ≈ 54.13 A
2. Circuit Breaker Size:
Instantaneous Trip = 8 × 54.13 ≈ 433.04 A
Inverse Trip = 2.5 × 54.13 ≈ 135.33 A
3. Contactor Currents:
Main Current = 0.58 × 54.13 ≈ 31.40 A
Delta Current = 0.58 × 54.13 ≈ 31.40 A
Star Current = 0.33 × 54.13 ≈ 17.86 A
4. Contactor Sizes (AC7b):
Main Size = 1.25 × 31.40 ≈ 39.25 A
Delta Size = 1.25 × 31.40 ≈ 39.25 A
Star Size = 1.25 × 17.86 ≈ 22.33 A
5. Thermal Overload Relay:
Delta Rating = 1.25 × 31.40 ≈ 39.25 A
Delta Set Value = 31.40 A
Main Rating = 1.25 × 31.40 ≈ 39.25 A
Main Set Value = 31.40 A