Auto Transformers

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Re: Auto Transformers

To get started, stop by your local electrical wholesale house. Pick up a catalog from Sq D, Cutler Hammer, GE. They all make and sell power transformers. This will give you some basic information.
 
Re: Auto Transformers

Autotransformer with regards to a starter? Or a buck-boost transformer for correcting or adjusting a voltage from 208-240v or 230-208v.
An autotransformer is wired to incorporate the primary and secondary winding is a series-parallel configuration to either reduce or increase the input voltage, the secondary winding is used to bump the voltage either up (boost) or down (buck). Because the primary and secondary windings are tied together, the secondary windings are often referred to as shut windings, it does not isolate the primary from the secondary. It also is a cost effective way to get a change in voltage by using a transformer that is much less kva (much less cost) as compared to using a common primary to secondary transformer for which the kva has to be sized for the load. For example is you have 208v and would like 240v you would consider a boost configuration. Again, remember that there is no isolation.
The autotransformer is also a cost effective way to provide reduced voltage starting for motors in that it is used to buck the voltage in the starting mode and then bypassed to the run mode for full voltage.
 
Re: Auto Transformers

By definition an autotransformer is a transformer with only one winding. A normal transformer will have at least two- a primary and a secondary. The primaries and secondaries are separate windings and as such are electrically isolated from each other. The number of turns in the primary vs the number of turns in the secondary and how you connect them determine whether the transformer will step up or step down the voltage and by how much.
An autotransformer (sometimes called an autoformer) with its one winding is electrically like a regular transformer with one end of the primary tied to one end of the secondary. This connection would be a "tap" on an autotransformer. A tap is the winding brought out to a terminal someplace between beginning and end. Between one end and the tap is the primary, the secondary is between the tap and the other end. Where the "tap" is positioned in relation to each end determines the turns ratios.
 
Re: Auto Transformers

Originally posted by hde_electric:
What is an auto transformer and what other types of transformers is there?
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Here is the way to make a Buck & Boost isolation (2-windings or more) transformer into an Autotransformer (1-winding). This is snipped from Acme. There is a link below to the whole text.

25) Your catalog indicates that a buck-boost transformer is suitable for connecting as an AUTOTRANSFORMER. What is the definition of an autotransformer and how does it differ from an isolation transformer?

An autotransformer is a transformer in which the primary (input) and the secondary (output) are electrically connected to each other. An isolation transformer, also known as an insulating transformer, has complete electrical separation between the primary (input) and the secondary (output).

An autotransformer changes or transforms only a portion of the electrical energy it transmits. The rest of the electrical energy flows directly thru the electrical connections between the primary and secondary. An isolation transformer (insulating transformer) changes or transforms all of the electrical energy it transmits.

Consequently an autotranskormer is smaller, fighter in weight, and less costly than a comparable KVA size insulating transformer.

Please refer to Question 27 for additional information on autotransformers.

Buck-boost transformers are frequently field-connected as autotransformers.
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Questions & Answers about Buck-Boost Transformers from Acme Power Tranmission Company

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Re: Auto Transformers

I have had more fun with autotransformer connections in some of my transformer classes I taught. I had some 1.0 KVA buck/boost transformers that I used in class. The transformers were 120/240 Pri and 12/24 Sec. Before I would get very far into the class I would ask the students how many different voltages we could get out of this transformer with a 120 pri. input. When I finished they were all suprised with the results. It really opened their eyes about transformers.

Roger
 
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