What is the difference, and an auto-transformer

To lower or raise the voltage applied transformers or autotransformers. Why, it would seem, for the same purposes, use different products? What is the fundamental difference between them and the similarity? In this article I will try to answer these questions. So, let's begin.

Table of contents

define

Briefly the principle of action

Advantages and disadvantages

conclusion

define

Let's give a definition of these two articles:

Transformer

Transformer - is a static electromagnetic device made of two or more interconnected induction coil wound around a magnetic core, and intended to transform by electromagnetic induction an alternating voltage of one value to another (or several) strains retaining vectors and frequency.

The main feature of the transformer is that it in the primary and secondary windings are galvanically isolated (i.e., there is no direct electrical contact). Schematically, it looks like this:

There are step-down transformers. In such apparatuses voltage is converted, for example, 110 kV at 35 kV or 10 kV, or else with 220 12 V.

Step-up transformers. In this case, the transformer is on the contrary increasing the operating voltage, for example, 6 kV to 110 kV TPP.

Isolating transformers. In this embodiment, the input voltage is identical to the voltage at the output. These products are intended for the formation of galvanic isolation.

autotransformer

Autotransformer call this kind of transformer, whose primary and secondary windings are electrically interconnected. At the same time the single coil in the presence of at least three output, connect to the add-on, you can get the voltage of various denominations.

Schematically, they can be represented as follows:

It should be emphasized that there is no auto-transformers electrical isolation, ie in the case of a fatal error (failure) primary high voltage may well be applied to the low side, that will disable all devices connected as load to low side.

Autotransformers are available with fixed output voltage and adjustable. By adjustable embodiments include such items as the LATR (laboratory autotransformer).

Auto-transformers can be either step-down and step-up, but the separation they can not be in principle (no galvanic isolation).

The number of windings in autotransformer directly related to the number of phases. In other words, if we want autotransformer single phase, it will be odnoobmotochnym, if a three-phase, the three-winding.

Briefly the principle of action

Note. Next will be considered the so-called ideal transformers in which the voltage drop is negligible. So, become a faithful following equation U1 = E1 and U2 = E2.

Let's talk briefly about the principles of operation of these two devices.

So, as we know, the transformer has at least a pair of coils that are wound on the core, and they are isolated from each other.

If the primary winding is energized from the mains or from any other power supply, the flowing it will generate a current magnetic flux which passes through the core and a secondary coil in the latter will bring EMF. The whole principle of interaction is implemented on the phenomenon of electromagnetic induction.

When this voltage difference of the primary winding and the secondary winding is the ratio of their turns (transformation coefficient).

Now, let's say a few words about autotransformer

Let us assume for the windings W1 autotransformer winding is connected a source of variable energy, and the coils W2 connected consumer. During the flow of alternating current in the winding of the autotransformer formed by an alternating magnetic flux in the coil forming an electromotive force which is directly dependent on the number of turns.

Means that portion of the winding, wherein the windings W1, U1 and respectively formed where W2 is formed U2.

Y is the transformation ratio of the autotransformer on the same principle as a conventional transformer by the following expression:

K = U1 / U2 = W1 / W2

Significant differences begin when considering the flowing currents.

Since we have a connected load, then the winding number of turns W2 c generated current I2.

In the upper half of the coil, where the number of turns is equal to (W1-W2) which carries current I1 will be very different from the current in the winding, wherein the windings W2. There will be a resultant current to flow which, according to Lenz's rule, is equal to I2-I1.

This means that the part of the coil, which runs the voltage supply to the consumer, the current will be significantly less than the current in the load, that is, the expression is true.

I2-I1 << I2

This effect can significantly reduce the costs of winding itself, which reduces the cost of the product.

Advantages and disadvantages

Pros and cons of the autotransformer

So, let's look at the advantages and disadvantages of first autotransformer.

Now let's learn about the pros and cons of already classic transformers

Application area

Classic transformer can be found almost everywhere, from the most common charge, to huge power plants on large high-voltage substations.

Autotransformers are also quite common, we all know LATR (laboratory autotransformer), but also the power of AT also occur in networks where there is earthed neutral.

conclusion

That's all I wanted to tell you about the differences and applications of transformers and autotransformers. If the article was useful to you, you will appreciate it, and thank you for your attention!