Why you need to be wary of buying a used transformer: the revelation of an electrician

There are always alternative offers on the market. If there is no opportunity or desire to buy a new one, you can purchase a used one. But not every purchase of stockpiled junk is a joy. Especially when it comes to electrical engineering. A participant of our forum shared his experience of working at an electromechanical plant, where power transformers are being repaired.

Our enterprise is a big dump

The plant where I worked is engaged in the repair and restoration of three-phase transformers and produces transformer substations. The enterprise is large and, one might say, not poor, but it looks like a big dump.

Why is that? Because part of the territory is littered with various electrical junk: old rusty transformers; obsolete substations and their parts; vacuum and other circuit breakers; mountains of aluminum and copper wires. And if you think that this is unnecessary scrap metal, then you are wrong. This is the raw material from which "candy transformers" and the insides of new substations are assembled.

What's in the factory

Half of the staff have no special education. The enterprise hires everyone who can tell the difference between a screwdriver and a lollipop from the first try. Salaries are small and “specialists” are raised locally.

The equipment that is required for the full repair of this electrical equipment has become obsolete in the last century. For example, winding machines date from the days when the first dogs went into space.

The oven for drying windings and active parts is also ancient, but works well. Even too good! Sometimes, after such a heat treatment, the insulating paper burns and falls off the wires.

The test bench does not work 70% of the functions. Some measurements are made on it, the product is run under voltage, and the rest of the parameters are written into the accompanying documentation from the head.

Of those that work normally in the shops, there is perhaps a crane-beam. The rest of the work is done mainly by hand, because "qualified" workers think that this is how it should be in such a production.

How the process works

In order to assemble a suitable transformer in this office, you need to have a tank with a lid - the rest will be found. Used transformers for refurbishment fall into four categories here.

1. Ideal. Which is closed inside and outwardly intact. In this category, the insulation on the windings is mostly broken.
2. A good one is one that burned out from the inside, but the tank is intact. On the active part, only the upper part and the switch are damaged.
3. Satisfactory. This category includes transformers that burned in the truest sense of the word. They have swollen tanks, distorted lids, only a yoke beam remains of the insides, the windings are melted.
4. All the rest. This is what a normal person would disdain to hand over to scrap metal. For example, damaged transformers that have been standing for ten years, or maybe twenty in the open air. From time to time, their gaskets collapsed and rainwater got inside. In general, soaked trash.

Housings

Tanks, depending on the degree of injury, undergo recovery. First, they are cleaned by hand using sandpaper and metal brushes. There is sandblasting at this enterprise, but there is no specialist. Nobody wants to inhale kilograms of dust for 23 thousand rubles a month. Yes, and do it on a homemade wretched installation.

After cleaning, defective tanks (housings) are straightened. On them, as on the car, putty is applied in layers. Then the tanks are painted solid gray. The manufacturer's plate is stuffed onto the case with a new one, and it is, of course, fake.

An important point! Many of these tanks have cooling radiators and cannot be cleaned inside. Radiators can contain moisture and rust. So when oil is poured into the tank, this dirt or water gets into it. And no one knows after what time and under what load the winding will break through again.

An important point! The tank may appear level, but the gap between the active part and the housing wall will be broken. Because of this, a short to the case may occur.

Good to know! If a transformer from the eighties is painted like a Zhiguli for sale and a new plate flaunts on it, then there is a catch. Usually the seller likes the phrase: "Stood in conservation." But why is there a centimeter layer of paint on it - the question. Always inspect the case of the product carefully. If you notice signs of car putty under the paint on it, refuse to buy.

Active part and windings

While the tanks are being restored, the engineer casts a spell on the entrails. New windings are rarely installed. In most cases, what is already there is restored. This is called rewind. The winding is unrolled, the old insulation is removed from the wire and the wire is rewound.

If the wire is broken somewhere, then this is not considered a reason to change it completely. The burnt area is removed and another wire is put in its place using a solder. The number of adhesions in a single winding can be overwhelming and shocking. I've seen six and it's in the low voltage winding!

If there is no wire of the required cross-section at the "warehouse" (factory dump), then you can put it thinner or thicker - the main thing keep the number of turns, and the engineer will somehow adjust the resistance to the permissible 2% in the windings and 4% in scheme. Here we must give credit to the engineer - he is a genius.

After the windings are ready, the locksmith gets down to business - they collect the active part, and the product goes to drying. More about switches - they are in trouble. I haven't seen any new ones in three years of work. These parts are so dilapidated that after the first switching the transformer may cease to live.

Next, the "candy" goes to the test bench. If the tests are passed, the assembly begins. The assembly is awful - everything inside breathes smoothly. The studs of the yoke beam cannot be tightened according to the norm - the dilapidated wooden parts of the active part sometimes do not stand up and break. Of the new, only insulators and gaskets are put on the transformer.

One more point. The winders are girls. They cannot properly pull the low voltage winding wire and this affects the quality of the product.

It is important to know! If, when turned on, the transformer hums strongly and even vibrates, it means that the winding wires are weakly stretched - poor quality. They also shake under voltage, making noise. Such a transformer will not last long.

And by the way, the buyer can be told that the windings are copper, but in fact they are aluminum. This can only be checked with a megohmmeter. But it is unlikely that a developer or a farmer will understand these intricacies.

About oil

If you think that new oil is poured into the transformer after repair, then you are mistaken. We fill in the separated. By the way, the separator is also ancient and often breaks. So when this shaitan machine is being repaired, new oil goes into the transformers.

One more nuance. Dry oil is stored in a container, at the bottom of which there is a twenty-centimeter layer of water! How so? It's simple: oil is lighter than water and therefore does not mix. There was once a case when a locksmith was asked to measure the oil with a stick with marks. He measured and mixed the layers a little. This substance was poured into a huge transformer "thousand-meter". After that, it was successfully burned.

Warning

If you are offered to buy a used transformer for three times cheaper, then keep in mind that it can be of such an assembly. If it is sold from a workshop or a repair company, then there are great chances that it will not live long.

And one more trick. If you bought such a product and it burned out when you first turned it on, then before making a claim, take a picture of the switch position. The fact is that when a specialist comes to you for an examination, he can put him between positions and then they will blame you for this.

Think sucked out of your finger? But no, I myself have received such requests from the director three times. To be honest, I never did it. But not because I am a saint, but because in two cases oil leaked out during transportation and they burned out from overheating. And in the third, the adjustment bar melted so that justice was etched in the metal forever.

Have you bought a used transformer? Write in the comments!

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