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From the tag info (highlight mine):

Electrical Machines are Electro-Mechanical energy converters. They maybe classified into motors (electrical -> mechanical), generators (mechanical -> electrical) and transformers (electrical -> electrical).

The inclusion of "resting" magneto-electric devices in that category is imho controversial, but that's not the point:

Since transformers are significantly different from motors and generators, a tag covering all three feels less helpful:

Whilst you cannot, without knowing the direction of power flow, tell whether a specific machine is a generator or a motor at any point in time, so it's helpful to have a general tag for both.

A transformer is a transformer, and no (intended) mode of operation changes that¹.

Since someone asking about a is likely to use that tag, shouldn't we exclude that usage from the tag description?


¹ could of course also be an electrical bonfire.

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    \$\begingroup\$ So what are these if not electric machines?? \$\endgroup\$ – pipe Nov 14 '19 at 18:37
  • \$\begingroup\$ They don't move so they are not machines we where thought in school. \$\endgroup\$ – winny Nov 20 '19 at 12:04
  • \$\begingroup\$ I suppose if you really stretch the definition, a rotary converter could be considered a type of transformer, and that's unambiguously a machine.... but as I said, that's really stretching the definition. \$\endgroup\$ – Hearth Nov 20 '19 at 13:43
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A reason for including transformers in the electric machinery category is that they are included in electric machinery textbooks. A good knowledge of transformers is required for learning about electric motors. The heart of the circuit model for an induction motor is a transformer.

A reason for not including it is that this is not a text book and using that tag is not all that likely to be helpful. Most people searching with that tag are not likely to be looking for questions about transformers.

I would be inclined to delete transformers from the tag.

From Wikipedia:

Other electromagnetic machines include the Amplidyne, Synchro, Metadyne, Eddy current clutch, Eddy current brake, Eddy current dynamometer, Hysteresis dynamometer, Rotary converter, and Ward Leonard set. A rotary converter is a combination of machines that act as a mechanical rectifier, inverter or frequency converter. The Ward Leonard set is a combination of machines used to provide speed control. Other machine combinations include the Kraemer and Scherbius systems.

There are electrostatic motor and generators, but I don't know of other electrostatic machines.

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Most transformers are not included in that tag description as written, only those that are "Electro-Mechanical energy converters", for example the rotary converter linked by Hearth in the comments.

It wouldn't hurt to clarify the tag description though... it could be as simple as inserting the mechanical requirement in the transformer sequence, e.g.

some transformers (electrical -> mechanical -> electrical).

Other transformers and power conditioners, including electrical -> magnetic -> electrical and electrical -> chemical -> electrical, are outside the scope as-written.

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  • \$\begingroup\$ True, the first sentence of that description does say electro-mechanical; there's the confusing side aspect that some books do say electrical machines are all machines converting electrical power to and from magnetic force (this is a bad translation from German) \$\endgroup\$ – Marcus Müller Nov 20 '19 at 17:58
  • \$\begingroup\$ I would not call rotary converters "transformers"; as I said in the earlier comment, that's really stretching the definition. That comment was me trying to rationalize why they were included in the first place--I do not agree that they should be included, personally. \$\endgroup\$ – Hearth Nov 21 '19 at 16:42

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