Auto-coupling means electromagnetic coupling. Ordinary transformers transfer energy through the electromagnetic coupling of the primary and secondary coils. There is no direct electrical connection between the primary and secondary sides. There is a direct electrical connection between the primary and secondary sides of the autotransformer. The low-voltage coil is part of the high-voltage coil.
The transformation ratio of the autotransformer is calculated the same as that of the general transformer! Simply divide the input voltage by the output voltage.
Two or more coils are wound on a closed iron core. When one coil is connected to an AC power source (the primary coil), an alternating current flows through the coil. This alternating current generates an alternating magnetic field in the iron core. Changing the main magnetic flux produces its own induced electromotive force in the primary coil, and at the same time, the mutual induction electromotive force is induced in the other coil (that is, the secondary coil). By changing the relationship between the primary and secondary coil turns ratio to change the primary and secondary coil terminal voltage to achieve voltage conversion, the general turns ratio is 1.5:1~2:1. Because the primary and secondary coils are directly connected, there is a risk of inter-level leakage. Therefore, it cannot be used as a running light transformer.
In the current power grid, autotransformers have only started to have a voltage level of 220KV, and they are mostly used as connection transformers between the power grids. There is almost no auto-transformation below 220KV. Autotransformers are used at lower voltages and are most often used as motor step-down start-ups. For dry-type transformers, its insulating medium is solid such as resin, and there is no insulating oil in oil-immersed transformers, so it is called For dry type. Due to poor heat dissipation conditions, dry-type transformers cannot be made large in capacity. Generally, there are only small and medium-sized transformers, and the voltage level is basically 35KV and below. However, there are already dry-type transformers with a rated voltage of 66kV or higher at home and abroad. Transformers can have a capacity of up to 30000kVA or even higher.
For the autotransformer, the input and output are shared. In short, a set of coils can be used as input and output. For step-up and step-down, different shaft heads are used to achieve If it is less than the shared coil, then this part of the shaft head is used for step-down, and if there are more shaft heads in the shared coil sector, then it is used as a step-up. According to the number of coils, we can distinguish between boosting and bucking.
Since the autotransformer is generally used in the protection equipment of the communication line, its calculated capacity is determined by the small fish. Therefore, the size of the autotransformer is relatively small, and the corresponding structural materials and effective materials are also reduced. Quite a lot, so he greatly reduced the cost of production. Although all aspects are smaller than other transformers, its transformation efficiency is very high.
Because of its simple structure, less materials, small size, and low cost, auto-voltage transformers are widely used in many industries. But it is rarely used in power systems, because the use of autotransformers in power systems will have adverse effects.
For an autotransformer, there is only one winding transformer, and when it is performing different tasks, its role will also produce a certain difference, and if it is used for step-down, then a part of the winding will be extracted It is used as a secondary winding, and when it is used as a booster, only a part of the wire is on the winding for the applied voltage, and the part for the primary and secondary is called the common winding, and for Some of the remaining parts are called series windings, so that different windings can form different principles of action.
Compared with other ordinary transformers, the autotransformer has a smaller and more beautiful appearance, and its own efficiency is also higher. Of course, one of the most prominent advantages is that its own capacity is relatively large, which is also a development in the modern power industry. Consistent, so for the autotransformer, the application is quite extensive.Several common usage forms of autotransformer