1. ECE 4411 Interpreting the Circle Diagram

2. ECE 4412 Graphical Interpretation The blocked rotor voltage, E BR, is assumed constant. P gap =E BR I r cosθ r is proportional to I r cosθ r. I r cosθ r is the projection of the current phasor on the horizontal axis.

3. ECE 4413 What happens when the load on the motor is increased? Start with the motor partially loaded and operating with a slip of 0.05. Increasing the shaft load will slow the motor down, increasing the slip. The magnitude and phase of the rotor current increase.

4. ECE 4414 Graphical Interpretation continued The current phasor elongates and rotates clockwise to a position that results in an I r cosθ r sufficient to carry the load. If the load continues to increase, a “breakdown” point will be reached where I r cosθ r decreases!