How does a soft-start autotransformer compare to a regular autotransformer?


I'm using some commercial kitchen appliances from the U.S. in Europe, so I need to transform the voltage from 230v to 115v. I have been learning about different autotransformers, and came across some that have 'soft-start' and those that don't.

As I understand it, soft-start ramps up the voltage as it is needed by the device instead of just giving the full voltage at once. Is that true?

What devices prefer an adjusted voltage to begin with? From what I've seen, soft-start autotransformers appear to be more expensive, so I'm guessing they are probably better all around, but I don't know. Perhaps the device wants the full power straight away. How would I decide whether to get a soft-start or...

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Circuit and function

An auto-transformer starter makes it possible to start squirrel-cage induction motors with reduced starting current, as the voltage across the motor is reduced during starting.

In contrast to the star-delta connection, only three motor leads and terminals are required. On starting, the motor is connected to the tappings of the auto-transformer; transformer contactor K2M and star contactor K1M are closed.

The motor starts at the voltage reduced by the transformer, with a correspondingly smaller current.

By this means the feeding current in comparison to direct starting would be reduced by the square of the transformer voltage ratio; nevertheless, it is in most cases noticeably higher, as it also covers the relatively high transformer losses.

Depending on the tapping and starting current ratio of the motor, the starting current lies at (1 … 5) · Ie. In contrast, the motor torque falls with the square of the voltage across the...

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An autotransformer is an electrical transformer containing only a singular winding, rather than separated primary and secondary windings. The single winding still allows for the performance of the same function as an ordinary transformer. In autotransformers, each opposing side of the coil acts as the primary side or the secondary side, depending on which side of the coil is connected to the load versus the power supply. There are at least three connections made to the coil between the two opposing sides that are draws on the voltage created by the autotransformer in order for the transformer to function as it was intended.

The primary function of a transformer is to transform the amount of voltage directed to a circuit by attaching the connection from the power supply to the load at a certain point within the transformer’s winding. Due to the fact that the amount of winding or turns within a transformer’s coil determines the amount of voltage released at any point...

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This single winding is “tapped” at various points along its length to provide a percentage of the primary voltage supply across its secondary load. Then the autotransformer has the usual magnetic core but only has one winding, which is common to both the primary and secondary circuits.

Therefore in an autotransformer the primary and secondary windings are linked together both electrically and magnetically. The main advantage of this type of transformer design is that it can be made a lot cheaper for the same VA rating, but the biggest disadvantage of an autotransformer is that it does not have the primary/secondary winding isolation of a conventional double wound transformer.

The section of winding designated as the primary part of the winding is connected to the AC power source with the secondary being part of this primary winding. An autotransformer can also be used to step the supply voltage up or down by reversing the connections. If the primary is the total...

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Auto transformer has construction similar to the normal transformer except that some part of winding is common to both the primary and secondary. A step down Auto transformer is shown below:

Step up transformer is shown below here:

Both the transformers shown above has fixed secondary voltage. There are some auto transformers, with variable output transformers. They are called as Variable output Auto transformers. They are also called as Dimerstat, Variac or simply Auto Transformers.
Edit 1: Thank you Vishu Rawat for asking me to answer this question.
Edit 2: I appreciate answers by:
Pavan Kumar (an auto transformer is a single winding transformer which transfers power from one circuit to another circuit through both conduction and induction).
Muralidhar Rao (Certain applications requiring only small step- up or step-down of voltage, a special variant of transformer is designed. That is Auto...

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The Star/Delta starter is probably the most commonly used reduced voltage starter, but in a large number of applications, the performance achieved is less than ideal, and in s

…ome cases, the damage and interference is much worse than that caused by a Direct On Line starter. The Star/Delta starter requires a six terminal motor that is delta connected at the supply voltage. The Star Delta starter employs three contactors to initially start the motor in a star connection, then after a period of time, to reconnect the motor to the supply in a delta connection. While in the star connection, the voltage across each winding is reduced by a factor of (1 /.'/'3) [1 divided by root three]. This results in a start-current reduction to (1 /.'/'3) [1 divided by root three] of the DOL start current and a start torque reduction to one third of the DOL start torque. If there is insufficient torque available while connected in star, the motor can only accelerate to a partial speed compared...
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What is AUTOTRANSFORMER? What does AUTOTRANSFORMER mean? AUTOTRANSFORMER meaning - AUTOTRANSFORMER definition - AUTOTRANSFORMER explanation. Source: article, adapted under license. SUBSCRIBE to our Google Earth flights channel - An autotransformer (sometimes called autostep down transformer) is an electrical transformer with only one winding. The "auto" (Greek for "self") prefix refers to the single coil acting alone and not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. In contrast, an ordinary transformer has separate primary and secondary windings which are not electrically connected. The winding has at least three taps where electrical connections are made. Since part of the winding does "double duty", autotransformers have the advantages of often being...

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Reduced Voltage Starter

Reduced voltage starter systems very often will use an autotransformer to adjust the voltage during starting. The autotransformer will have preset voltage allowances, also known as taps. Taps allow for control over the power output to the motor by determining the initial voltage and inrush current. The taps are typically set to either 50%, 65%, or 80% of full-voltage, allowing for a starting current of 25%, 42% or 64%.

For example, a centrifugal compressor will be set at a 65% tap, allowing for 42% of full inrush current. If the autotransformer was set at the 50% tap, there would not be enough current going to the motor to allow it to run, while the 80% tap would allow for more current than was necessary.

Once the motor gets up to full voltage, the autotransformer will then be switched out of circuit, and the motor will be able to run across the line at full voltage.

A reduced voltage starter can come with solid-state motor...

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