To date, the most common and good are three-phase transformers. Each of the three sides must have a corresponding winding. Each selected winding must necessarily be connected according to a specific scheme that fits optimally.
The scheme of the transformer with two windings.
There are many types of connections for all transformer windings. The three simplest circuits should be used in combination to ensure the normal operation of the installation. But to determine the specific type, you need to take into account some tips and options.
Parameters that are important to consider when choosing a scheme
As a rule, it is very difficult to decide for yourself what kind of winding scheme for a transformer installation to choose. And even if you will attract specialists for such a business, it is important to know the basic parameters that must be considered during the selection process. These include:
The table of values of three-phase transformers.
- Transformer power. It is important to take into account not only the total power, but also its changing values in individual areas. After all, modern transformer installations differ in their power values in different phases.
- Power scheme The device can be powered both from the mains and from the converter. In this case, even the network power can be from three or four wires.
- Accounting savings. As a rule, during the choice of schemes, it is the cost-effectiveness of using materials for windings that plays one of the most important roles. The less materials needed for the circuit, the more profitable the winding will be.
- The voltage level is similar to the power taken into account both in general terms and in terms of performance in individual areas.
- Symmetry or load asymmetry. It depends entirely on a symmetric or asymmetric voltage circuit. Accordingly, a certain value is achieved by symmetry.
So, these parameters are considered to be the main when choosing a winding connection scheme for a transformer. Only after the calculations should be taken as a more detailed selection of the scheme, which is very important for the effective operation of installations.Back to table of contents
The simplest types of windings
Circuit armor type three-phase transformer.
There are three main options for transformer windings. This connection is a star, zigzag and triangle. Each is characterized by certain parameters that perform their functions. Therefore, it is extremely important to choose the type of connection correctly. To understand what is at stake, consider all three options in more detail.
The connection of the windings with a triangle (D, d) is made in the form of a ring, where all three phases are connected in series. It is the most common and popular today. The connection makes it possible to circulate freely to the current inside the ring. This is the so-called third harmonic. If at least one part of the transformer does not provide such a triangle (or ring), the current inside cannot move freely, which will distort the voltage very much.
The star connection (Y, y) is the presence of all the ends of the winding at a single neutral point. The result is a figure resembling a star, in the middle of which a neutrality will always remain. It allows you to protect the device from overvoltage. You can also always create the necessary grounding parameters.
A zigzag (Z, z) connection of transformer windings must necessarily have two taps in which zero-sequence currents will circulate.
Figure 1. Wiring connection diagram for transformers of the Yd type.
So there will be a good balancing of currents and voltages in the transformer. In this case, the resistance will completely depend on the magnetic dispersion between the zigzag taps.
So, we can conclude that for the standard three-phase transformer all three schemes can be used comprehensively. In this case, for the side with the highest voltage, it is preferable to choose a star connection, and make the remaining sides zigzag and triangular windings.Back to table of contents
Basic 5 winding schemes for a three-phase transformer
But no transformer can contain only a specific type of winding. Therefore, for three-phase types of transformers specific group schemes are applied. There are only 5 of the most common schemes. They are identified by Latin letters, which denote the type of winding (described above), and numbers indicating phase shifts. Additionally, Latin letters N and n can be entered, which denote the output of the neutral clamp for the primary and secondary windings, respectively, on the terminal parts.
The connection of the windings for transformer installations of the Yd type, for example, as in fig. 1, used for step-up three-phase installations. If the primary and secondary windings are connected by a triangle, then the harmonic of all currents will flow in a closed circuit, and the magnetic flux will be almost completely absent, which is very beneficial. You can make the primary winding method of the star. But its neutral part must be reliably grounded by a choke. This is also considered very convenient.
Figure 2. Wiring connection type Dy.
The Dy type circuit is mainly used for step-down transformers of high power. An example of such a scheme is shown in the photo (Fig. 2). This is very good, especially under conditions of asymmetric loads, since the neutral part will allow the use of both phase and linear voltage types at the expense of good grounding. Optimal use of this circuit winding for transformers that operate on low voltage networks.
The connection of the windings of power transformers of the Dz and Yz type is used for lowering types of installations whose main power is very low. Here, a zigzag connection is usually used as the main one, and its neutral point is output to a terminal block for using voltages across phases. But often, instead of a zigzag, they use a star shape. This is done only for the reason that the star implies a smaller amount of copper used for the winding, which makes it possible to save.
These two types are good to use when it is necessary to distribute the voltage symmetrically in one part of the transformer. In all other cases, their use is not recommended, as it may simply decrease the level of operation of the device.
Another most common circuit for a three-phase transformer is considered to be a circuit like Yy. Her example is shown in Fig. 3. It implies the use of a star-type winding only. It is not the most convenient, however, it is successfully used for transformers with not very high rated power. We have to deal with the need to compensate for the influence of higher current harmonics.
For neutralization, it is advisable to additionally introduce a compensation winding in the form of a triangle. This is especially important if, in a transformer, in addition to a triangle, another star is used that gives a neutral point.Back to table of contents
Useful tips for group schemes
But there are many modified transformers. Therefore, it makes sense to consider some useful tips on connecting windings in individual cases. It is very important to consider here the parameters of the transformer core and the number of rods in the core.
Figure 3. Connection diagram of windings of type Yy.
- If the core contains 5 rods, then it is extremely important to correctly wind the winding in the form of a triangle. In this case, it is the triangle that will provoke damping of the harmonic flows, which will ensure their alignment along the sinusoid. Thus, the voltage will be almost impossible to distort. In the core with five rods, it is necessary to do the triangular winding exactly where the measurements show a pronounced shortage of currents along the sine wave and uneven voltage spikes.
- If the transformer on the transformer must be used for charging, then it is best to make its winding in the form of a star, and the nearby side - a triangle. This will give a good level for the main resistance of the sequence to zero and provide a balance for the currents. The other side of the transformer installation can be performed as a triangle, and zigzag. Such a group scheme is suitable in this case for a core with five or three rods.
- For some types of transformer installations, it is advisable to use compensation windings. By sense, these are the same compounds with a triangle, only they will already be tertiary. For the secondary voltage, the zigzag pattern will be used, and for the primary one, the connection can be made a triangle. Such a scheme for connecting the transformer windings provides for a good reduction in the zero-sequence impedance and maximum voltage equalization.
Winding circuits are a kind of voltage regulators. They can not only equalize it, but also change the value, which is very important in some cases.
So, what is the connection of the windings of power transformers, you now know.
Using simple actions, it is possible to achieve the required voltage level at the installation and its displacement between the sides relative to each other.