An autotransformer is a transformer with only one winding. When used as a step-down transformer, a portion of the turns are extracted from the winding as the secondary winding; when used as a step-up transformer, the external voltage is only applied to a portion of the turns of the winding. superior. Usually, the part of the winding that belongs to both the primary and secondary windings is called the common winding, and the remaining part is called the series winding. Compared with ordinary transformers of the same capacity, self-coupling transformers are not only smaller in size, but also more efficient, and the transformer capacity is larger. The higher the voltage. This advantage becomes more prominent. Therefore, with the development of power systems, the increase of voltage levels and the increase of transmission capacity, auto-coupling transformers have been widely used due to their large capacity, low loss and low cost.
1. An autotransformer is a special transformer in which the output and input share a set of coils. The voltage boost and voltage reduction are realized with different taps. The tap voltage of the part with less than the common coil will decrease. The voltage of the tap of the part with more common coils will increase. high.
⒉In fact, the principle is the same as that of an ordinary transformer, except that its primary coil is its secondary coil. In a general transformer, the primary coil on the left uses electromagnetic induction to cause the secondary coil on the right to generate voltage. The autotransformer affects itself.
⒊An autotransformer is a transformer with only one winding. When used as a step-down transformer, a part of the turns are extracted from the winding as the secondary winding; when used as a step-up transformer, the external voltage is only applied to part of the winding. On the turn. Usually the part of the winding that belongs to both the primary and secondary windings is called the common winding, and the rest of the autotransformer is called the series winding. Compared with ordinary transformers of the same capacity, autotransformers are not only smaller in size, but also more efficient. The larger the capacity, the higher the voltage. This advantage becomes more prominent. Therefore, with the development of power systems, the increase of voltage levels and the increase of transmission capacity, autotransformers have been widely used due to their large capacity, low loss and low cost.
According to the principle of electromagnetic induction, the three-phase autotransformer does not need to have separate primary windings and secondary windings. Only one coil can achieve the purpose of voltage conversion. In Figure 1, when the primary winding W1 of the transformer is connected to the AC power supply U1 When , the voltage drop of each turn of the original winding of the transformer is evenly distributed among the original windings 1 and 2 of the transformer. The voltage of the secondary winding W2 of the transformer is equal to the voltage of each turn of the original winding multiplied by the number of turns 3,4. With U1 unchanged, Changing the ratio of W1 and W2 will result in different U2 values. This kind of transformer in which the primary and secondary windings are directly connected in series and self-coupled is called an autotransformer, also called a single-turn transformer.
The primary and secondary windings of an ordinary transformer are insulated from each other and are only connected magnetically but not electrically. Depending on the number of coil groups, this kind of transformer can be divided into a double-turn transformer or a multi-turn transformer. Based on the principle of electromagnetic induction It can be seen that there is no need to have separate primary winding and secondary winding. Only one coil can achieve the purpose of voltage conversion. In Figure 1, when the primary winding W1 is connected to the AC power supply U1, the voltage drop of each turn of the primary winding, the average voltage Distributed among the original windings 1 and 2, the voltage of the auxiliary winding W2 is equal to the voltage per turn of the original winding multiplied by the number of turns of 3 and 4. While U1 remains unchanged, changing the ratio of W1 and W2 will result in different U2 values. This kind of primary and secondary windings are directly connected in series and self-coupled transformers are called autotransformers, also called single-turn transformers. Various operating modes of autotransformers. The relationship between the voltage, current and number of turns in the autotransformer and the transformer, both ：U1/U2=W1/W2=I2/I1=K
The biggest feature of the autotransformer is that the secondary winding is part of the original winding (auto-step-down transformer in Figure 1), or the primary winding is part of the secondary winding (auto-step-up transformer in Figure 2).
The current directions of the primary and secondary windings of the autotransformer are opposite to those of ordinary transformers.
Neglecting the excitation current and losses of the transformer, the following relationship can be obtained
Voltage reduction: I2=I1+I,I=I2-I1
Boost: I2=I1-I,I=I1-I2
P1=U1I1,P2=U2I2
In the formula:
I1 is the primary winding current, I2 is the secondary winding current
U1 is the primary winding voltage, U2 is the secondary winding voltage
P1 is the primary winding power, P2 is the secondary winding power
