Which has a higher starting current, a synchronous motor or an asynchronous motor?

Asynchronous motors have a higher starting current, because the excitation current of synchronous motors increases gradually; that is, after startup, their main current rises as the excitation current increases. It is therefore understandable that the starting current of synchronous motors can be controlled, allowing for a lower current compared to asynchronous motors. Personal opinion, for reference only.

The stator windings of a synchronous motor with structure n and an asynchronous motor are the same; the main difference lies in the structure of the rotor. The rotor of a synchronous motor has a DC excitation winding, so an external excitation power supply is required to supply current through slip rings ； The rotor of an asynchronous motor is a short-circuited winding that generates current through electromagnetic induction. In contrast, synchronous motors are more complex and costly. l Purpose n Synchronous motors are mostly used in large generators. Asynchronous motors are almost exclusively used in electric drive applications. Synchronous motors can flexibly adjust the voltage and current phase on the input side through excitation, that is, the power factor ； The power factor of asynchronous motors is not adjustable, and it generally ranges between 0.75 and 0.85. Therefore, in large factories where asynchronous motors are used extensively, a synchronous motor can be added as a condenser machine to regulate the power factor at the interface between the factory and the power grid. However, due to the high cost and extensive maintenance requirements of synchronous motors, capacitive power factor compensation is generally used nowadays. Furthermore, some early inverters that used thyristors required load commutation since these devices did not have the ability to turn off on their own; in such cases, synchronous motors were needed. The efficiency of synchronous motors is slightly higher than that of asynchronous motors; when selecting motors with a capacity of over 2000 KW, it is generally necessary to consider whether to use synchronous motors. However, since synchronous machines have excitation windings and slip rings, they require operators with high skill levels to control the excitation; moreover, their maintenance requirements are greater compared to the low-maintenance nature of asynchronous motors ； Therefore, for motors below 2500 KW nowadays, asynchronous motors are the preferred choice. At low power levels, the difference in efficiency becomes negligible. When using an inverter, it is necessary to disconnect the motor from the power grid and connect the inverter instead. After connecting to the inverter, the power on the grid side is independent of the motor and depends only on the inverter. Therefore, unless the user already has a synchronous motor, an asynchronous motor should be chosen, as both the frequency converter and the motor are inexpensive. Of course, if an early-type load-commutated frequency converter is used, a synchronous motor must be selected for the motor – this is the requirement of the frequency converter regarding the motor. In simple terms: both synchronous and asynchronous motors are AC-powered motors that rotate thanks to power supplied by a 50-hertz AC grid. In an asynchronous motor, alternating current is applied to the stator, generating a rotating magnetic field; the rotor then generates its own magnetic field as a result of induction, and it is the interaction between these two magnetic fields that causes the rotor to rotate in sync with the stator’s rotating magnetic field. The rotor rotates more slowly than this magnetic field, resulting in a difference in speed; hence it is called an asynchronous motor. In a synchronous motor, just like in the asynchronous case, the stator produces a magnetic field, but the rotor has a constant magnetic field created by direct current, which allows it to rotate in sync with the stator’s magnetic field – hence the name synchronous motor. Asynchronous motors are simple, cost-effective, and easy to install, use, and maintain, which is why they are widely used. Their disadvantages include low efficiency and a low power factor, which can be detrimental to the power grid. Synchronous motors, on the other hand, have high efficiency; they can handle capacitive loads and help improve the power factor of the power grid. They are therefore used in large industrial and mining equipment.

Basically the same; it’s just a bit smaller for synchronous operation, as even synchronous machines start asynchronously, and no current is applied to the rotor’s coils at the time of startup. It follows the same principle as mentioned above, so I won’t go into further detail here. The advantages of synchronous machines are: 1. They can absorb reactive power from the power grid; 2. they are capable of driving heavy loads; 3. their speed does not decrease as the load increases. This post was last edited by HandsomeToTheExtreme on Feb 26, 2009 at 10:59.]