1. What is Locked Rotor Current?

The locked rotor current is the current drawn by an electric motor when its rotor is prevented from rotating while full voltage is applied. This represents the maximum current the motor will draw under normal operating conditions.

2. How Does the Calculator Work?

The calculator uses the locked rotor current equation:

Where:

• \( I_{lr} \) — Locked rotor current (amperes)
• \( V \) — Applied voltage (volts)
• \( Z_{lr} \) — Locked rotor impedance (ohms)

Explanation: The equation calculates the current drawn when the motor rotor is locked (not rotating) based on the applied voltage and the motor's impedance in the locked condition.

3. Importance of Locked Rotor Current Calculation

Details: Knowing the locked rotor current is essential for proper circuit protection design, motor starting characteristic analysis, and ensuring electrical systems can handle motor starting currents.

4. Using the Calculator

Tips: Enter voltage in volts and locked rotor impedance in ohms. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is locked rotor current important?
A: It helps determine the required rating for motor protection devices and assesses the impact of motor starting on the electrical system.

Q2: How does locked rotor current compare to normal operating current?
A: Locked rotor current is typically 5-8 times higher than the motor's full load current.

Q3: What factors affect locked rotor current?
A: Main factors are applied voltage and motor impedance. Higher voltage or lower impedance increases locked rotor current.

Q4: How long can a motor withstand locked rotor current?
A: Typically only a few seconds before overheating occurs. Protection devices must operate quickly under locked rotor conditions.

Q5: Can this calculator be used for single-phase motors?
A: No, this equation is specifically for three-phase motors. Single-phase motors require a different calculation.