1. What is Locked Rotor Torque?

Locked rotor torque is the torque produced by an electric motor when its rotor is stationary (locked) and full voltage is applied. It represents the starting torque capability of the motor.

2. How Does the Calculator Work?

The calculator uses the locked rotor torque equation:

Where:

• \( I_{lr} \) — Locked rotor current (amps)
• \( R_r \) — Rotor resistance (ohms)
• \( \omega \) — Angular frequency (rad/s)
• \( s \) — Slip (1 for locked rotor condition)

Explanation: The equation calculates the torque developed when the rotor is stationary, which is crucial for motor starting performance.

3. Importance of Locked Rotor Torque

Details: Locked rotor torque determines whether a motor can start a load. It must exceed the load torque at standstill for successful starting.

4. Using the Calculator

Tips: Enter locked rotor current in amps, rotor resistance in ohms, and angular frequency in rad/s. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: Why is slip (s) equal to 1 for locked rotor condition?
A: Slip is defined as (ω_sync - ω_rotor)/ω_sync. When rotor is locked, ω_rotor=0, so s=1.

Q2: What is a typical locked rotor torque value?
A: For standard NEMA design motors, locked rotor torque typically ranges from 60% to 300% of full-load torque.

Q3: How does rotor resistance affect locked rotor torque?
A: Higher rotor resistance increases locked rotor torque but reduces efficiency at normal operating speeds.

Q4: What's the difference between locked rotor torque and breakdown torque?
A: Locked rotor torque occurs at zero speed, while breakdown torque is the maximum torque the motor can produce at any speed.

Q5: How is locked rotor current related to locked rotor torque?
A: Both are high during starting, but while current is proportional to voltage, torque is proportional to voltage squared.