Maintaining the continuity of process operation after voltage sag or power interruption

In a refinery, all process units have a continuous operation. A continuous supply of electricity is important to maintain process unit operation. Voltage sag due to faults in the power supply system or motors reacceleration may result in a costly shutdown if motors driving essential loads stop during these voltages disturbances resulting mainly from contactor drop or tripping of adjustable speed drive. This paper considers two action lines. The first one approaches the sensitivity of critical electrical equipment to voltage sags while the second discusses systems exposed to sag and service continuity. Solutions implemented in motors control circuits and sets of parameters in adjustable speed drive are presented. The implementation of equipment solutions may cause other problems in the electrical system, like voltage sag due to motor reacceleration. A dynamic stability simulation to analyze motor reacceleration and the results of these simulations are presented.