Laboratory latr its scheme is the number of turns. Latr (laboratory autotransformer) - device, principle of operation, types and applications
In the laboratory stands of my college, laboratory autotransformers (LATRs) regularly fail. It so happened that through trial and error I managed to master the technology of their repair. On the this moment I have already managed to repair three laboratory autotransformers, and I rewound LATRs in my dorm room. I would be glad if the LATR rewinding technology described here turns out to be useful to someone. Yes, this is my first article, so do not judge strictly :-)
To begin with, a short course of the LATR device (see figure).
LATR has two windings connected in series. Mains voltage is applied to the primary winding (this must be taken into account when rewinding). The secondary winding is connected to the primary. It is designed for voltage from 0-240 V. Voltage is applied to terminals A and N in the magnetic circuit, a magnetic flux is created that induces a current in the windings taken from terminals A1 and N.
Let's start with the fact that you need to determine the diameter of the wire. This can be done with a caliper. To do this, you must first measure the diameter of the native wire, and then, based on this, look for a suitable wire for us. You can take a piece of old wire and then compare it with the desired sample.
Then you need to determine the length of the wire. This can be done using the usual mathematical expression: L=lturn×W 1.2 cm,
where L is the required wire length (in centimeters), l turn is the length of one turn; W 1.2 - the number of turns of the secondary and primary windings.
1) Calculation of the number of turns by formulas. This method is quite simple, but there is a high probability of making an error in it, for example, in calculations or in measurements of the area of the magnetic circuit window. This method is given below:
We find the power of the autotransformer: P=U×I,
where U - output voltage, I - maximum load current (usually written in LATR).
The overall power is found: Rg \u003d 1.9 * Sc * S,
where 1.9 is the factor for toroidal transformers.
Required number of turns per volt:
K = 35/Sc, where 35 is a factor for toroidal transformers.
Determine the number of turns; W1 = U1*K
Determine the dimensions of the core: Sc=((Dc-dc)/2)×h, So=πxd2/4,
where Sc is the area of the transformer core; So is the area of the window.
2) The second option is rather laborious, but reliable (I used this method when rewinding LATRs). This method of determining the number of turns consists in the fact that you need to unwind the old winding and at the same time count the number of turns. It needs: a leaf and a pen in order not to go astray, a coil or a piece of wood to wind the old winding there, as well as nerves of steel and patience so as not to throw it out the window after a hundred counted turns.
After that, we rest and relax after the work done, because then you need maximum care and patience. When you're done, let's start cooking. workplace. It is desirable that it be well lit and that everything can be placed necessary items such as a desk with a lamp or a chair in a well-lit room.
For ease of rewinding, it is better to first wind a new wire on a wooden blank as shown in the picture:
There is no fundamental difference in how the wire is settled, on the inner diameter of the window. But in order to lay the required number of turns, it is necessary to wind the first turn to it tightly, then wind the second turn, and lay the third turn on top between the first and second and repeat until we wind the required number of turns on a voltage of 220V. After that, we make the conclusion of the network clamp and from this conclusion we wind the secondary winding. On the outer diameter of the magnetic circuit window, all turns must be laid in series one by one, as shown in the figure.
After the rewinding is completed, the winding must be impregnated with varnish to improve the insulating properties and to fix the wound wire in its place. Since a lot of varnish is not required here, you can use any one resistant to temperatures up to 105 ° C. After impregnation with varnish, leave the autotransformer to dry for a couple of hours. For best results, place in a warm place. Leave the room where the work was carried out and it is very desirable to open the window for ventilation.
After drying, it is necessary to make a path for stress relief. This can be done with a knife or sanding paper. We make a path from the outer window to the inner one about 3 cm long (shown in the figure below).
Half a century ago, the laboratory autotransformer was very common. Today, the electronic LATR, the circuit of which every radio amateur should have, has many modifications. Old models had a current-collecting contact located on the secondary winding, which made it possible to smoothly change the value of the output voltage, made it possible to quickly change the voltage when connecting various laboratory devices, changing the heating intensity of the soldering tip, adjusting electric lighting, changing the speed of the electric motor and much more. Of particular importance is LATR as a voltage stabilization device, which is very important when setting up various devices.
Modern LATR is used in almost every home to stabilize the voltage.
Today, when electronic consumer goods have flooded store shelves, it has become a problem for a simple radio amateur to acquire a reliable voltage regulator. Of course, you can find an industrial design. But they are often too expensive and bulky, and this is not always suitable for home conditions. So many radio amateurs have to "reinvent the wheel" by creating an electronic LATR with their own hands.
A simple voltage regulator
One of the simplest LATR models, the scheme of which is shown in Fig. 1, is also available to beginners. The voltage regulated by the device is from 0 to 220 volts. The power of this model is from 25 to 500 watts. You can increase the power of the regulator up to 1.5 kW, for this, thyristors VD1 and VD2 should be installed on radiators.
These thyristors (VD1 and VD2) are connected in parallel with the load R1. They pass current in opposite directions. When the device is connected to the network, these thyristors are closed, and the capacitors C1 and C2 are charged through the resistor R5. The magnitude of the voltage received at the load is changed, if necessary, by a variable resistor R5. Together with capacitors (C1 and C2), it creates a phase-shifting circuit.
Rice. 2. Scheme of LATR, giving a sinusoidal voltage without interference in the system.
A feature of this technical solution is the use of both half-cycles alternating current, therefore, not half power is used for the load, but full.
The disadvantage of this circuit (paying for simplicity) must be considered that the shape of the alternating voltage on the load is not strictly sinusoidal, which is due to the specifics of the operation of thyristors. This may cause interference on the network. To fix the problem, in addition to the circuit, you can install filters in series with the load (chokes), for example, take them from a faulty TV.
For the manufacture of a laboratory autotransformer (LATR) with their own hands, many are pushed by an excess of low-quality regulators on the electrical market. You can also use a copy of the industrial type, however, such samples are too large and expensive. It is because of this that their use at home is difficult.
What is an electronic LATR?
Autotransformers are needed to smoothly change the voltage current frequency 50-60 Hz during various electrical work. They are also often used when it is necessary to reduce or increase the alternating voltage for household or building electrical equipment.
Transformers are electrical equipment, which is equipped with several windings connected inductively. It is used to convert electrical energy according to the level of voltage or current.
By the way, electronic LATR began to be widely used 50 years ago. Previously, the device was equipped with a current-collecting contact. It was placed on the secondary winding. So it turned out to smoothly adjust the output voltage.
When connected various laboratory devices, there was a variant of operational voltage change. For example, if desired, it was possible to change the degree of heating of the soldering iron, adjust the speed of the electric motor, the brightness of the lighting, and so on.
Currently, LATR has various modifications. In general, it is a transformer that converts alternating voltage of one magnitude to another. Such a device serves as a voltage stabilizer. Its main difference is the ability to adjust the voltage at the output of the equipment.
Exists different types autotransformers:
- Single phase;
- Three-phase.
The last type is three single-phase LATRs installed in a single structure. However, few people want to become its owner. Both three-phase and single-phase autotransformers are equipped voltmeter and adjustment scale.
Scope of LATR
The autotransformer is used in various fields of activity, among them:
- Metallurgical production;
- Public utilities;
- Chemical and oil industries;
- Technology production.
In addition, it is needed for the following work: the manufacture of household appliances, the study of electrical equipment in laboratories, the adjustment and testing of equipment, the creation of television receivers.
In addition, LATR often used in educational institutions for conducting experiments in chemistry and physics lessons. It can even be found in the composition of the devices of some voltage stabilizers. It is also applied as the additional equipment to recorders and machine tools. Almost in all laboratory research in the form of a transformer, it is LATR that is used, since it has a simple design and is easy to operate.
An autotransformer, unlike a stabilizer, which is used only in unstable networks and creates a voltage of 220V at the output with a different error of 2-5%, gives the exact specified voltage.
According to climatic parameters, the use of these devices is allowed at a height of 2000 meters, but the load current has to be reduced by 2.5% when lifting every 500 m.
The main disadvantages and advantages of an autotransformer
The main advantage of LATR is higher efficiency, because only some part of the power is transformed. It is especially important if the input and output voltages are slightly different.
Their disadvantage is that there is no electrical insulation between the windings. Although the neutral wire has grounding in industrial power networks, therefore, this factor will not play a special role, in addition, less copper and steel for cores are used for windings, as a result, less weight and dimensions. As a result, you can save a lot.
The first option is a voltage change device
If you are a novice electrician, then it is better to try first to make a simple LATR model, which will be regulated by a voltage device - from 0-220 volts. According to this scheme, the autotransformer has power - from 25-500 W.
To increase the power of the regulator to 1.5 kW, you need to put thyristors VD 1 and 2 on radiators. They are connected in parallel with the load R 1. These thyristors pass current in opposite directions. When the device is connected to the network, they are closed, and the capacitors C 1 and 2 begin to charge from the resistor R 5. If necessary, they also change the voltage during the load. In addition, this variable resistor, together with the capacitors, forms a phase-shifting circuit.
This technical solution makes it possible use two half cycles at once alternating current. As a result, full power is applied to the load, not half.
The only drawback of the circuit is that the shape of the alternating voltage during the load, due to the specifics of the operation of the thyristors, is not sinusoidal. All this leads to network interference. To correct the problem in the circuit, it is enough to build filters in series with the load. They can be pulled out of a broken TV.
The second option is a voltage regulator with a transformer
A device that does not cause interference in the network and gives a sinusoidal voltage is more difficult to assemble than the previous one. LATR, the scheme of which has biopolar VT 1, in principle, you can also do it yourself. Moreover, the transistor serves as a regulatory element in the device. The power in it depends on the load. It works like a rheostat. This model allows you to change the operating voltage not only with reactive loads, but also with active ones.
However, the presented autotransformer circuit is also not ideal. Its disadvantage is that a functioning regulating transistor generates a lot of heat. To eliminate the disadvantage, you will need a powerful heat sink radiator, the area of \u200b\u200bwhich is at least 250 cm².
In this case, a transformer T 1 is used. It should have a secondary voltage of about 6-10 V and power approximately 12-15 W. The diode bridge VD 6 rectifies the current, which subsequently passes to the transistor VT 1 in any half-cycle through VD 5 and VD 2. The base current of the transistor is regulated by a variable resistor R 1, thereby changing the characteristics of the load current.
Voltmeter PV 1 control the size of the voltage at the output of the autotransformer. It is used with a voltage calculation from 250-300 V. If it becomes necessary to increase the load, then it is worth replacing the VD 5-VD 2 diodes and the VD 1 transistor with more powerful ones. Naturally, this will be followed by an expansion of the radiator area.
As you can see, to assemble LATR with your own hands, perhaps you just need to have a little knowledge in this area and purchase everything necessary materials.
LATR - adjustable laboratory autotransformer - one of the types of autotransformers, which is an autotransformer of relatively low power, and is designed to regulate the alternating voltage (alternating current) supplied to the load from a single-phase or three-phase network alternating current.
At the heart of LATR, like any other network transformer, is a core made of electrical steel. But on the toroidal core of LATR, unlike other types of network transformers, there is only one winding (primary), part of which can act as a secondary, and the number of turns of the secondary winding can be quickly adjusted by the user, this is the distinctive feature of LATR from simple autotransformers .
To regulate the number of turns per secondary winding, the design of the autotransformer has a rotary knob connected to a sliding carbon brush. When the handle is turned, the brush slides from turn to turn along the winding, so it is regulated.
One of the secondary terminals of the laboratory autotransformer is directly connected to the sliding brush. The second secondary output is shared with the input side of the network. Consumers are connected to the output terminals of LATR, and its input terminals are connected to a single-phase or three-phase power supply. In a single-phase LATR, there is one core and one winding, and in a three-phase one, there are three cores, and each has one winding.
The voltage at the output of LATR can be either greater than the input or less, for example, for a single-phase network, the adjustable range is from 0 to 250 volts, and for a three-phase network, from 0 to 450 volts. It is noteworthy that the efficiency of LATR is higher, the closer the output voltage is to the input voltage, and can reach 99%. Output voltage form - .
On the front panel of LATR there is a voltmeter of the secondary circuit for the possibility of operational control of overload and more accurate setting of the output voltage. The LATR case has ventilation openings through which the magnetic circuit and windings are naturally cooled by air.
Laboratory autotransformers are used in laboratories for research purposes, for testing AC equipment, and simply for manually stabilizing the mains voltage, if it is currently below the required rating.
Of course, if the voltage in the network is constantly jumping, then the autotransformer will not save, you will need a full-fledged stabilizer. In other cases, LATR is just what you need to fine-tune the voltage for the current task. Such tasks can be: setting up industrial equipment, testing highly sensitive equipment, setting up radio-electronic devices, powering low-voltage equipment, charging batteries, etc.
Since the LATR has only one winding common for the primary and secondary circuits, the current of the secondary winding is also common for the primary and secondary circuits. From this point of view, it is obvious that the current of the secondary winding and the primary current in the common turns are directed oppositely, therefore total current equal to the difference between the currents I1 and I2, that is, I2 - I1 \u003d I12 - the current in the common turns. So it turns out that with a value of the secondary voltage close to the input, the common turns can be wound with a wire of a smaller cross section than in the case of a two-winding transformer.
The design feature of LATR forces us to separate the concepts of "power throughput" and "design power". The calculated power is that which is transmitted from the primary winding to the secondary circuit by means of electromagnetic induction through the core, as in a conventional two-winding transformer, and the throughput power is the sum of the throughput power and the power that is transmitted only through the electrical component, that is, without the participation of the magnetic core induction.
It turns out that in addition to the calculated power, a purely electric power equal to U2*I1. This is why autotransformers require a smaller magnetic core to carry the same power compared to conventional two-winding transformers. This is the reason for the higher efficiency of autotransformers. In addition, less copper is required for the wire.
So, with a small transformation ratio, LATR boasts the following advantages: efficiency up to 99.8%, smaller size of the magnetic circuit, lower consumption of materials. And all this is due to the presence of an electrical connection between the primary and secondary circuits. On the other hand, the absence between the circuits leads to the danger of phase current from the output terminals of the LATR and even from one of the terminals, therefore, it is necessary to be extremely careful when working with a laboratory autotransformer.
Transformer devices provide normal functioning various electrical engineering. Laboratory autotransformer (LATR) performs the functions of a kind of power supply for mains voltage variable type. What is LATR, what are its features and the basic principle of operation, will be discussed further.
Peculiarities
Considering what LATR is, it should be noted that this is a type of autotransformer. It is characterized by low power, it does not require a state register. The principle of operation, which the laboratory adjusting autotransformer has, is to adjust the voltage of an alternating type single-phase(on the left in the photo) or three-phase networks (right).
The LATR scheme includes a toroidal-type steel core. It has only one circuit. This device does not have two separate windings. The contours are aligned. One part can be assigned to the primary type turns, and the other part to the secondary type turns. Adjusting autotransformer LATR has enough a simple circuit. The user can independently adjust the number of turns of the secondary winding. This distinguishes the presented variety of units from other transformers. We wrote about how to assemble LATR with our own hands.
Design
It becomes possible to regulate the presented unit through the presence of a rotary knob in the design. With its help, the number of turns of the secondary circuit is set. The handle is connected to the carbon brush. Adjustable autotransformers allow you to control the windings after turning on the equipment. In this case, the brush, according to the instructions, slides along the contour, setting the transformation index.
One of the outputs of the secondary winding is connected to the carbon brush. Its other end is connected to the input side of the network. Consumers are connected to the output terminals, and they, in turn, are connected to the mains. This makes the use of the equipment efficient and convenient.
A voltmeter is installed on the front panel of the device. He takes readings of the secondary circuit. This allows you to quickly respond to overloads. The voltmeter provides the ability to make adjustments accurately.
The case has a ventilation grille. This provides natural cooling of the magnetic drive.
Varieties
There is equipment designed to regulate the voltage of a three-phase or single-phase network. In the second version, the electronic LATR has one winding and one core. The three-phase unit includes three cores in its design. Each of them has one winding.
LATRs can both lower and increase the voltage. This is their main feature. Single-phase varieties create a voltage in the network from 0 to 250 V. LATR three-phase (380 V in the network) can adjust the range from 0 to 450 V.
It should be noted that the efficiency of both types of devices is high. It reaches 99%. This creates a sinusoidal output voltage.
Application
LATRs are used in research centers, laboratories for testing AC equipment. Sometimes such devices are needed to stabilize mains voltage. For example, at the moment of its insufficient level in the network at the moment.
However, its scope is limited. If there are constant drops, jumps in the network, the use of an autotransformer will be meaningless. In this case, you will need to install a stabilizer. The main purpose of LATR is to fine-tune the voltage to perform various research tasks and tests.
Such equipment may be required in the process of setting up industrial devices, highly sensitive equipment, and radio electronics. They provide the correct power supply for equipment operating at low voltage. They are also used when charging batteries.
Having considered the main features of laboratory autotransformers, you can correctly use the unit for various purposes, increasing the efficiency and convenience of setting up various equipment.
