Field Current

[landbattery]

Hello,
I am trying to find out what is field current in a motor. REally don't understand if there's a correlation if field current versus motor current??

 

[ScottyUK]

Field current indicates that it is a synchronous machine of some type, be it generator or motor. There's no real difference in terms of the machine, just what it drives or is driven by.

In an islanded generator the field current controls the voltage produced by the generator within certain limits. For a motor or generator connected to a large system the field current can be used to control the power factor of the machine within certain limits. In this respect field current does have the ability to vary the current in the stator, with minimum stator current occuring at unity power factor. The limits are related to machine stability at low field currents and by thermal considerations in either the stator or rotor at high field currents.


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If we learn from our mistakes I'm getting a great education!

 

[landbattery]

thank you

 

[Skogsgurra]

Or is it about "field" current aka excitation current in a vector drive plus asynchronous motor?

If that is the case, you will need to look up basic vector control methods. It is not the simplest thing to grasp. Needs some thinking and studying.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[oftenlost]

Unless you are referring to a DC machine where field current affects torque and speed.

 

[ScottyUK]

Oftenlost - I totally overlooked DC machines. Thanks.

skogs,

I've never heard that called 'field current' before. 'Magnetising current' or 'excitation current' I ve heard. Am I alone?


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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

Scotty,

It is sometimes referred to as field current. The other two field currents (in synchronous machines and DC machines) are so obvious that I don't think anyone in electrical engineering needs to ask about them. The ASM field current (Id) is less obvious and may generate questions.

Also, the question contains "correlation field current versus motor current" and that implies that the OP thinks about two currents flowing in one set of wires, which you have in an ASM.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...