A synchronous motor fails to pull into step under several circumstances;
The fundamental causes may be attributed to its functional characteristics and environmental influences.
Here are the key conditions that can lead to this failure:
1). Low Excitation
2). Excessive Load
3). High Friction
4). Incorrect Timing of DC Excitation
5). Single Phasing
6). Short Circuit (or) Open Circuit Conditions
7). Sensitivity to Load Changes
8). Damper Winding Issues
Factors That Cause a Failure to Pull into Step
1). Low Excitation
Low field current makes it difficult to achieve high excitation thus cannot maintain the motor stability needed. If excitation is insufficient, the rotor cannot stay in phase with the rotating magnetic field of the stator thus failing in pulling into step.
2). Excessive Load
If the motor is subjected to load greater than the rated load, then the motor loses synchronism. The rise in expectation of torque may outstrip the motor’s capacity to follow the supply frequency leading to stall.
3). High Friction
While at synchronous speed, different mechanical problems such as high friction in bearings of other rotating equipment reduce the rotor’s capability of achieving synchronous speed as desired. This mechanical resistance can hinder the rotor from reading the magnetic lines of the stator’s magnetic field.
4). Incorrect Timing of DC Excitation
The application of the DC excitation should be done at the right time in order to achieve synchronization. If the excitation is applied too early or too late during startup, failure of synchronizing the rotor with the stator’s magnetic field may arise resulting to operational losses or failures.
5). Single Phasing
If one phase is missing in a three-harmonic supply and the motor carries on functioning, it shall not be capable of achieving synchronization. This condition can lead to an overheating of some components and potential damage by unequal current flow.
6). Short Circuit (or) Open Circuit Conditions
Any short circuit or open circuit in one of the phases is potentially fatal for proper functioning of the system. This results in an inability to produce enough torque for the behavior in question, and the motor may actually be damaged in the process, namely.
7). Sensitivity to Load Changes
Synchronous motors cannot be made to operate satisfactorily during load variation. Any significant change in load can cause unsynchronized loss of synchronism than making it more futile to pull into excessive Load.
8). Damper Winding Issues
Although dampers act to support the system during start-up and sudden load fluctuations, no support for maintaining synchronism might be provided if the concerned windings are ill designed or have been developed from the system.
Conclusion
Some of the considerations that are normally practiced to achieve a stable operation of stat worlds are levels of excitation, Load conditions, and mechanical structure of machines employed. This can be done by practicing the basic abilities of stepping and sensitive movements as discussed above to try and eliminate failures in pulling into step and improving the total motor performances.
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