Performance of synchronous motors loss-of-synchronism protection
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.
Loss-of-Field Protection for Synchronous Machines [includes discussion]
THE COMPLETE or partial loss of the d-c supply to a large synchronous machine can have serious consequences. This may be loss of stability in the power system with the resulting major loss of service or costly damage to the machine itself. On the other hand, it is desirable to maintain the machine on the line as long as possible supplying kilowatts to the system.
Advantages of Large Solid-Pole Brushless Synchronous Motors for Centrifugal Compressor Drives
There is an increasing requirement for self-starting electric motors to drive large centrifugal compressors. The solid-pole brushless synchronous motor meets these requirements with capabilities beyond the practical limitations of the laminated-pole motor. The solid-pole construction and the slip energy to be absorbed during starting are considered together with the loss and temperature distribution within the poleshoes. The uses of vendor data for equivalent circuits, reactances, and time constants are considered in relation to starting, and differences between solid-and laminated-pole motors are highlighted. An improved brushless excitation circuit is described.