Performance of synchronous motors loss-of-synchronism protection

• Published in: 2017 Petroleum and Chemical Industry Technical Conference (PCIC) pp. 71 - 78
• Main Authors: Donolo, Marcos, Donolo, Pablo, Patel, Subhash, Yedidi, Vinod
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01-09-2017
• Subjects: Impedance; out-of-step; pull out protection; Reactive power; Relays; Stators; Synchronous motor loss-of-synchronism; Synchronous motors; Trajectory; Voltage fluctuations
• ISSN: 2161-8127
• DOI: 10.1109/PCICON.2017.8188725

Synchronous motors are rarely designed to operate asynchronously for extended periods of time. When a synchronous motor experiences a mechanical load exceeding its pull out torque, it enters asynchronous operation, under which the interaction between the stator and rotor magnetic fields causes damaging mechanical stress and vibrations. Also, induced currents in the rotor cause extra heating that quickly damages the rotor windings. Asynchronous operation must be detected and dealt with by allowing time for resynchronization or by tripping the motor to avoid thermal overload and damage. Two protection elements are often used to detect asynchronous motor operation: the power factor element and the out-of-step element. This paper compares the performance of the two elements to protect a 20 MW synchronous motor subjected to pull out conditions.