Characteristics of autotransformers: 1. Autotransformers are small in size, light in weight, easy to transport, and low in cost; 2. Since the short-circuit impedance per unit value of autotransformers is smaller than that of double-winding transformers, the voltage changes The rate is small, but the short-circuit current is large; 3. The primary side and the secondary side are not only magnetically connected, but also electrically connected.
Autotransformer refers to a transformer whose primary and secondary windings are on the same winding. The primary and secondary windings are directly connected in series and are self-coupled. . According to the structure, it can also be subdivided into adjustable pressure type and fixed type. Autocoupling means electromagnetic coupling. Ordinary transformers transfer energy through electromagnetic coupling of the primary and secondary coils. The primary and secondary sides have no direct electrical connection. The primary and secondary sides of the autotransformer have direct electrical connection. Its low-voltage coil It is part of the high voltage coil. Protective equipment such as autotransformers are also used in the protective equipment of communication lines.
Main features of autotransformer
1. Autotransformer is small in size, light in weight, easy to transport and low in cost.
Because the calculated capacity of the autotransformer is less than the rated capacity. Therefore, under the same rated capacity, the main size of the autotransformer is smaller, and the effective materials (silicon steel sheets and wires) and structural materials (steel) are reduced accordingly, thereby reducing the cost. The reduction of effective materials results in a corresponding reduction in copper and iron losses, so the efficiency of the autotransformer is higher. At the same time, due to the reduction of main dimensions and mass, a single transformer with a larger capacity can be manufactured within acceptable transportation conditions. But usually only when k≤2 in the autotransformer, the above advantages are obvious.
2. Since the short-circuit impedance per unit value of the autotransformer is smaller than that of the double-winding transformer, the voltage change rate is smaller, but the short-circuit current is larger.
3. The primary side and the secondary side are not only magnetically connected, but also electrically connected, while ordinary transformers are only magnetically connected.
Because there is a direct electrical connection between the primary and secondary parts of the autotransformer, when the high-voltage side is over-voltage, it will cause severe over-voltage on the low-voltage side. In order to avoid this danger, lightning arresters must be installed on both the primary and secondary windings. Do not think that the primary and secondary windings are connected in series. If the primary winding is installed, the secondary winding can be omitted.
4. In general transformers, the on-load voltage regulating device is often connected to the grounded neutral point, so that the voltage level of the voltage regulating device can be lower than when the voltage is regulated at the line end. The neutral point voltage regulation side of the autotransformer will bring about the so-called related voltage regulation problems. Therefore, when the autotransformer is required to have on-load voltage regulation, only the line-end voltage regulation method can be used.
5. Since the autotransformer winding is composed of two parts: a primary winding and a common winding, the number of turns of the primary winding is correspondingly reduced compared to the number and height of the primary winding of an ordinary transformer, as well as the current of the common winding and the leakage reactance generated.
6. If the autotransformer is equipped with a third winding, its third winding will occupy the common winding capacity, affecting the autotransformer operating mode and switching capacity.
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