First, let's figure out what the transformer is for and what it is. This is an electric machine designed to change voltage. They are different depending on the destination. There are transformers of current, voltage, matching, welding, power, measuring. Everyone has different tasks, but they are uniquely united by the principle of action. Any transformers operate on alternating current. There are no such direct current devices. All of them have primary and secondary windings.
What is called the primary and what is the secondary winding?
The primary is the one on which the voltage comes, and the second is the one with which it is removed. Suppose we have a transformer that converts 220 V AC to 12 V. In this case, the primary winding is one that is 220 V. But the transformers can not only lower, but also increase the voltage. Thus, by connecting 12 V AC to the previously indicated secondary winding, we can remove 220 V from the primary. Thus, they change places.
In some cases, there may be several secondary windings. For example, in old televisions there were devices with one primary winding and many secondary ones, the voltage on which varied from 3.3 to 90 V. In any case, the transformer serves to convert voltages and currents to optimal values.
Law of energy conservation
It should be understood that this unit does not take energy out of nowhere. For example, take a transformer with a primary voltage of 220 V and a current of 5 A. This means that its power is 1100 watts. From the secondary winding of 22 V, we can remove the current no more than 50 A. Translating into watts, we get the same 1100 watts. We will not remove more power from the secondary winding. When you try to do this, the device will simply fail. Thus, it becomes clear what the transformer is for. To convert AC to DC. Next, we describe in more detail about each type of such devices.
Instrument Transformers
Such devices are used to reduce the values to acceptable for measuring devices. They are used in instrumentation. You can also meet such devices in microprocessor technology. There they work as a sensor that sends signals of different levels to the board, depending on what the latter "decides" on the further operation of the device.
As a rule, they have high accuracy and are not intended to power consumers. Examples of measuring transformers are the devices below for converting current and voltage. We will try to explain their purpose as detailed as possible.
Current transformers
What are these devices for? They are designed to reduce the current to acceptable measuring equipment. In fact, they are intermediate equipment between the conductors from which it is necessary to remove the value of the quantity, and the measuring mechanism. Such transformers are used, as already mentioned, in measuring instruments, protection equipment and automation. They are connected in this way: the primary winding has several turns and is switched on sequentially to the load, and the secondary winding is connected to the minimum possible resistance of the protective or measuring equipment.
Typically, such transformers are supplied with the equipment itself, since minor changes in the load resistance will affect the accuracy of the measurements, and the protection equipment will not work properly. The design feature and the method of connecting such devices make it impossible to power the consumer.
Voltage transformers
This type of device is not used to power consumers, but is necessary to create a galvanic isolation between the high-voltage and low-voltage parts. The manufacturing method is no different from the power types of devices with the same name. There is still a primary and secondary winding, the wire cross section is quite low, which does not allow it to be used to power consumers.
For example, take a kilovoltmeter. The fact is that it’s too expensive to build a device that would hold a high voltage. Therefore, a voltage transformer is installed between the measuring probes, which take the value of the values, and the device. It converts high values to an acceptable measuring mechanism (approximately 100 V). This measure allows you to not make changes to the measuring mechanism. To some extent, this connection scheme allows you to protect the electrician who conducts the measurements.
They are also used for installation in various automated control and protection systems. Now you know what voltage transformers are for. Let's move on to the next type - welding devices of the same name.
Power transformers
These are more powerful devices that many of you have seen. Next, we will describe in detail what the power transformers are for. They are needed to increase / decrease the voltage by means of electromagnetic induction to the value that is necessary for the consumer. In the case of these devices, the word “consumer” means production and residential buildings.
The most striking example are devices that reduce 6 (10) kV to an acceptable 380 V, which already in a single phase in combination with the middle line feed our homes with the necessary 220 V. And an example of such a step-up transformer can be found in the microwave, where one of the 220 B makes 2 kV necessary for the operation of the magnetron. High-voltage units (over 1000 V) are almost always three-phase, and they are subdivided into oil or air cooling devices, as well as according to the climatic version and the voltage of the primary winding.
A feature of three-phase transformers is that, depending on the inclusion of the windings (star-delta), you can change the operating voltage by 1.73 times. Suppose this unit, connected by a 6 kV triangle, can work in a 10 kV network, if, of course, the manufacturer took care of this possibility from the side of isolation. There are transformers such as the above, three-phase and single-phase. Designed devices for working with various capacities depending on the needs of the consumer.
Single-phase transformers, which were previously used as power supplies, are now actively replaced by various electronic converters, which have greater efficiency, less weight and dimensions. Also, power devices can be divided according to the type of magnetic circuit design into rod and armored ones.
The transformer with a core magnetic circuit is designed in such a way that it is mounted on 2 coils on a U-shaped part, and the yoke is closed on top. The advantage is that the elements do not actually touch each other.
In the armored magnetic circuit, the coil is mounted on a W-shaped part. The section on which the conductors are located is usually first wound as a primary, and then, through a heat-resistant splitter, as a secondary. The advantage is enhanced mechanical winding protection.
There are also toroidal cores, but they are made of ferrite rings, because it is unprofitable to build such a structure from a lined magnetic core. Such units are usually used in electronics and operate at high frequencies.
Welding transformers
What are these devices for? In fact, they are independent units. That is, a welding transformer is not a strapping that ensures the operation of any device, but it is itself a full-fledged device. The purpose of such an apparatus is to lower the mains voltage to a relatively low, approximately 50-60 V, and provide a large current.
With such a voltage, a rather short arc breaks through, but a truly huge current provides it with great power. Thanks to the last parameter, metal is welded or cut.
Such transformers, as a rule, have a current adjustment. This is necessary to change the diameter and type of welding electrode. True, welding transformers for domestic use are increasingly being replaced by inverters. Which is not surprising, because the welding converter has lower efficiency. It strongly puts the mains voltage, consuming large currents on the primary winding, has a large weight, low mobility, it heats up pretty much compared to inverter devices.
Now you know how the welding transformer works and what it is for.
Matching
A transformer of this type is used in various multi-stage circuits to match the resistance between different parts of the circuit. You can meet him in a tube sound amplifier. Usually in such devices it is a weekend.
So what is a load matching transformer for? For example, the operating voltage of the lamps in the audio amplifier is 70-90 V, but the current is scanty. Such voltage cannot be applied to the speakers, which means that it is reduced to an acceptable voltage and, accordingly, the current rises.
The purpose of such a transformer is to lower the voltage or increase to a value necessary for a particular unit of the device.
Conclusion
All devices for converting current and voltage are united by the principle of action. The key parameters that you should pay attention to when buying: the voltage of the primary and secondary windings, frequency, power factor and, accordingly, power and output current.
In everyday life, this unit is almost never used. After all, the welding transformer replaced the inverter, and its analogs in the power supplies have already replaced the electronic voltage converters. This is done due to the fact that the devices usually have, in comparison with electronic, a large weight, and they are also not economically advantageous from the large consumption of non-ferrous metal in production and expensive repairs. Soon, only transformer substations will remain in production, but only in those places where it will not be possible to replace them with electronic components.
In this article we tried to explain what transformers are for, and talked a little about their main types.