Transformer Winding Book In Hindi Pdf Free Download

In the good old times it was a matter of fact that every electronic hobbyist or technician would wind himself any power transformers he needed, and rewind any that burned out. Unfortunately, nowadays transformer winding is fast becoming a lost art, and I have seen many people despair about where to find some very specific transformer, or pull their hair out about the cost of having one professionally wound to specifications.

Since I started in electronics, as a 12 year old boy, I have always wound my own transformers. I started using the basic, but useful instructions provided in The Radio Amateur's Handbook of the time, and later I came to better understand how transformers work, which enabled me to optimize a given transformer for the intended application.

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Following a request by many readers of my web site, I've added this page, which is complementary to the previously published Transformers and coils. You should first read (and understand!) that page, before trying to design any transformer. Then come to this more practically-oriented page, to learn some tricks and hints about the design process, and about hands-on winding.

This page addresses mainly single-phase power transformers in the power range from about 1 watt to 10,000 watts, operating at line frequencies, but much of what's described here can be applied to a wide range of other transformers too.

Let's start with the materials. To make a typical transformer, you need the iron laminations for the core, enameled copper wire of several different diameters for the windings, a bobbin (or some material to make one), insulating material to apply between wire layers, between windings, around the whole winding assembly, and on exposed wires, and in most cases it's also a good idea to use an impregnation varnish.

The photo here shows several stacks of iron E-I laminations, two coils of wire (with cardboard protecting the wire from damage), one roll of thick, stiff Pressspan, another roll of NMN laminate (we will soon see what that is), two small bundles of spaghetti for wire protection, and a can of transformer varnish. Add to this some glue, cotton straps, ropes, adhesive tape, terminals, bolts, angle iron, and other small material, and that's it.

All these materials are sold by companies specializing in transformers and parts for transformers. Enameled wire is also sold by many other distributors, but is usually cheapest at the places that sell it together with the other materials. You will have to dig into the phone book or some other directory to find these companies, since they don't usually have a shiny nice store in the downtown shopping mall!

In any E-I lamination you are likely to encounter, the center leg is twice as wide as each of the other parts. This is because the entire magnetic flux has to go through the center leg, but then splits up, with one half of the flux returning through each of the side legs. If you ever come across a lamination that has all three legs of the same width, then you are looking at a lamination intended for three phase transformers!

Such an economy E-I lamination like shown here has completely fixed proportions, beyond the rule above, that stem from the need to cut the I out of the winding window of two E's facing each other: If the center leg is 2 units wide, then the window is 1 x 3 units, the total E is 6 x 4 units, the I is 1 x 6 units, and so on.

Not all laminations follow the "economy" proportions, though. Here is an example of a lamination that comes in one piece, instead of being divided into an E and an I, and that has the windows proportionally much larger than the E-I lamination shown above. Such a lamination is a bit more expensive to make, because the steel cut from the windows is wasted, unless the manufacturer can find some other use for it. But being able to accomodate a much large winding assembly, it has some advantages in certain cases.

These "non-economy" laminations were quite usual in Europe, many years ago, but nowadays copper is so much more expensive than steel, that transformers are usually designed to use more steel and less copper. And for that goal, the economy lamination is very well suited. So you won't very often come across a lamination like this, unless you are restoring antique equipment.

The laminations should be thin, and reasonably well insulated from each other, to reduce eddy currents to an insignificant value. Typical thicknesses vary from 0.2 to 0.5mm, but higher frequency transformers (audio) use much thinner ones, while extremely large transformers might use slightly thicker ones.

The insulation is often applied at the factory that makes the big rolls of steel sheet, even before stamping the E's and I's. Different kinds of insulation are used: A thin oxide layer, a thin layer of enamel, or any of several chemical processes. Antique transformers sometimes even used very thin paper!

When I was young, patient and overly eager to do things right, I painted each and every E and I for my transformers, using diluted transformer varnish, to make a thin, nice layer. The photo shows the steel for a 200 watt transformer, drying. Later, getting old and lazy, I noticed that the layer of rust on old, recycled laminations is more than enough insulation, and that the very thin and imperfect insulation that comes on new laminations is enough too, even if it takes only a light scratch with the multimeter's test probe to puncture it and get through to the steel. We don't need perfect insulation between the sheets! We only need enough resistance to reduce eddy currents to a low level.

Transformer steel is not all born alike. Manufacturers will provide data sheets about their products (often on their web sites), where you can see what they offer. There are usually many grades, with vastly different loss characteristics. At a given flux density and frequency, a good material might have ten times less loss than a cheap material! So it pays to look, investigate, and decide intelligently what to buy. Thinner sheets normally have lower loss, and the rest of the secret lies in the exact alloy. In any case, you need to know what material you have, to be able to make a meaningful transformer design!

Some transformer steel is grain-oriented. That means that when rolling the steel sheets, a process is used to align the crystalline grains in the direction of the rolling. This kind of material has particularly good behavior when the magnetic flux is aligned with the direction in which the sheet was rolled, but is worse than standard material in the perpendicular direction. Such grain-oriented material is ideal for toroidal cores, which are made by coiling up a long strip of steel, but is not a large improvement for E-I laminations, because in these a significant portion of the material has to work with the flux perpendicular to the rolling direction.

Thick wires usually are coated with a sort of enamel that is very tough, an excellent insulator, highly heat-resistant, highly resistant to solvents, and that clings to copper even better than dirt does to children! This enamel is usually yellowish clear, so that the wire coated in it looks mostly copper-colored, but many exceptions exist. To solder the ends of these wires, it's necessary to scrape off the enamel, using a sharp knife or similar tool. This procedure would be too difficult with a thin, fragile wire, so that these thin wires are instead covered with an enamel that has most of the same characteristics of the other one, except the heat resistance: It will melt and turn into solder flux at a temperature a common soldering iron easily achieves! This allows easily soldering these wires, without previously stripping them. But transformers using this latter kind of wire enamel cannot survive temperatures as high as those using only the former kind of wire enamel. The red wire on the right side in this photo has this kind of enamel. But be careful with colors! The clear wire on the extreme left side also has solderable enamel, while the dark violet one in the middle is of the non-melting variety!

Here is a wire table for AWG wire. It shows the AWG number, the diameter in millimeters excluding the enamel, the approximate typical total diameter including the enamel (but this varies somewhat), the cross sectional copper area in square millimeters, the area of the square of window space occupied by that wire in a transformer (including the enamel, of course), the current carrying capacity at a typical, average value of current density, the resistance in ohms per meter, and finally how many meters of that wire come in one kilogram, because enamelled wire is usually bought by weight, not length.

Modern transformers of small to moderate size are usually wound on plastic bobbins. Here you can see simple ones. Some bobbins have pins or terminals molded into them, others have one or two divisions. Some don't have the slits for terminals, which the ones shown here do have.

Typically for a given size of E-I laminations, bobbins will be available in two or three sizes, accomodating different numbers of steel sheets. So you can vary the amount of steel in your transformer not only by choosing the lamination size, but also the height of the lamination stack!

Here is a little transformer using a divided (or split) bobbin. This is very practical, because it completely separates the primary from the secondary winding, making it much easier to achieve the degree of insulation required for safety. More about that later.

You must make the inner dimensions of the bobbin core a tad larger than the transformer center leg, but JUST a tad, no more, unless you want to waste valuable winding space! The sides can be made pretty tight to the size of the laminations, because if they don't fit at the end, they are easily enough cut or filed down, even after the winding has been made. But the length of the bobbin must be smaller than the window length of the core, by as much as 2 or 3%, plus any tolerances of your manufacture! Because it is critically important that the E's and I's can touch each other properly, without being kept separated by a bobbin that deformed during winding, and grew! e24fc04721