Applications for Synchronous Motors

PF = 1.00

Why people do not google? it is there do you know?

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The workhorse of our technical world is the general purpose 3~ single speed AC squirrel cage induction motor. It is simple, sturdy, very reliable and cheap, like in "not expensive." If not abused and properly maintained it can last a lifetime. Their starting circuits are relatively simple also. They are used wherever single speed drives are satisfactory. Wherever variable speed is required, variable speed drives are used. Much more expensive, but if needed, then that's it. So I fail to understand the "point" in your question. Are you saying that in India variable drives are used instead of single speed motors? Well, perhaps the engineers who run these plants have their reasons for it, reasons that are not immediately apparent to a casual outside observer. Why don't you try to find out. Then get back to us and tell us.

Synchronous motors find application in those areas where constant speed is a strict requirement. Ex. Reciprocating compressors.

They are also used as synchronous condensers to improve power factor of an electrical system. An excerpt from wikipedia will make this point more clear:

The leading power factor operation of synchronous motor finds application in power factor correction. Normally, all the loads connected to the power supply grid run in lagging power factor, which increases reactive power consumption in the grid, thus contributing to additional losses. In such cases, a synchronous motor with no load is connected to the grid and is run over-excited, so that the leading power factor created by synchronous motor compensates the existing lagging power factor in the grid and the overall power factor is brought close to 1 (unity power factor). If unity power factor is maintained in a grid, reactive power losses diminish to zero, increasing the efficiency of the grid. This operation of synchronous motor in over-excited mode to correct the power factor is sometimes called as Synchronous condenser.

For all practical purposes, an induction motor is considered as constant speed motor. The speed of the induction motors drops when the machine is loaded. However, this speed drop is negligible.

Synchronous motors require additional auxiliaries like excitation system. Synchronous motors are costly when compared to IM. For a given power output, the size of a synchronous motor is more when compared with corresponding IM. Hence, IM's are prefered over synchronous motors except in those cases which demand a strict constant speed.

Hai Vasu,

Hope you may find below info helpful:

1. Synch motors are costlier and need more maintenance than Sq cage induction motors, generally speaking.

2. Synch motors are more efficient and also economical when the ratings are high like 8MW and above. GE has a good paper on the subject in their website which says in case of low speed applications, even a 2MW Synch motor can be preferred.

The synchronious motor is a constant speed motor for all its rated loads. the motor can be run at lagging, unity and leading power factor depending on the field exitation voltage levels. synchronous motors are run over exited to enable it act as a synchronous condenser.

The leading power factor operation of the synchronous motor finds application in power factor correction.

The synchronous motor is one of the best industrial drive motors but for its cumbersome nature and unusual starting process. More so the component parts are too many and is capable of hindering periodic maintance.

Dickson.

As you guessed, they are used where you want constant speed such as a tape recorder or record player. Tesla coils use them for rotary spark gaps.