| Reduced voltage at the motor terminal will decrease the available torque to drive the load. As supply voltage to the motor decreases during a voltage sag event, motor speed also decreases. Depending on the voltage sag characteristic, the motor speed may or may not recover to its normal operating speed when the voltage recovers to its normal level. Motor behavior after a voltage sag event is similar to the motor starting process, which involves large inrush currents. Recovery from the voltage sag event may take the motor offline through the motor protection relay settings. In this thesis, the motor ride-through capability during a voltage sag event is analyzed using PSCAD, a time-domain simulation program for multi-phase power systems. A thorough review of existing medium voltage (MV) induction motor protection principles is presented. A comparison of these principles is also made with typical response to voltage sags, assuming the motor stays online. The critical factors affecting the motor's ride through capability are identified. Recommendations are made for properly setting the devices for the motor protection scheme. |
