3-Phase Motor Power Theory
Comprehensive analysis of three-phase motor power calculations and electrical principles.
-
Electrical Parameters
- Line Voltage (VL): √3 × Phase Voltage (VP)
- Line Current (IL): √3 × Phase Current (IP) (Δ)
- Power Factor Range: 0.80 to 0.95 typical
- Efficiency Range: 85% to 96% (NEMA Premium)
-
Power Calculations
- Real Power (P) = √3 × VL × IL × PF (watts)
- Apparent Power (S) = √3 × VL × IL (VA)
- Reactive Power (Q) = √3 × VL × IL × sin(φ) (VAR)
- Horsepower = (P × 1.341)/1000 (mechanical output)
-
Motor Characteristics
- Starting Current: 6-8× rated current
- Locked Rotor Code: A-H (NEMA)
- Service Factor: 1.15-1.25 typical
- Temperature Rise: 40°C to 80°C (class B-F)
-
Performance Factors
- Voltage Unbalance: Maximum 2% allowed
- Slip: 2-5% at full load (induction)
- Speed-Torque Relationship: T ∝ V²
- Altitude Derating: >3300ft (1000m)
-
Protection Parameters
- Overload Trip Class: 10, 20, 30
- Short Circuit Protection: Type 2 coordination
- Ground Fault: 5A or 20% rated current
- Phase Loss Protection: Required >5HP
-
Efficiency Standards
- IE1: Standard Efficiency
- IE2: High Efficiency
- IE3: Premium Efficiency
- IE4: Super Premium Efficiency