Selection Tips for Autotransformers


Release time:

2024-07-04

Autotransformers are special transformers that share a secondary and primary side, also known as single-winding transformers. For autotransformers, the following features are worth our attention:

Autotransformers are special transformers that share a secondary and primary side, also known as single-winding transformers.

For autotransformers, the following features are worth our attention:

1. Due to the shared winding, under the same rated capacity, the main dimensions of the autotransformer are smaller, and the effective materials (silicon steel sheets and wires) and structural materials (steel) are reduced accordingly, thereby reducing costs.

2. Copper loss and iron loss are also reduced due to the reduction of materials, which indirectly improves efficiency.

3. The short-circuit impedance rating of the autotransformer is smaller than that of the double-winding transformer, so the voltage change rate is smaller, but the short-circuit current is larger.

4. There is a direct electrical connection between the primary and secondary sides. When the high-voltage side is over-voltage, it will cause serious over-voltage on the low-voltage side. Lightning arresters are required to be installed on both the primary and secondary sides.

5. When the autotransformer is on-load voltage regulation, only the line-end voltage regulation method can be used.

Of course, during use, the autotransformer has the following disadvantages due to its structural characteristics, which we cannot ignore

1. There is an electrical connection between the high and medium voltage windings of the autotransformer, and its short-circuit impedance is only (1-1/K) square times that of an ordinary double-winding transformer of the same capacity.

2. The high and medium voltage windings are directly electrically connected, which makes it difficult to adjust the voltage. The current mainstream method is to install a voltage regulating device that changes the position of the tap with load or to install an additional transformer on the high and medium voltage lines. The cost is relatively expensive and also affects the operation

3. It makes the overvoltage protection of the winding complex and the relay protection complex.

For the autotransformer, in addition to the above advantages and disadvantages, the following issues need to be considered in its selection: transformer ratio, transformer operation mode, short-circuit current level, relay protection and electrical layout and transportation and other related aspects.

It is more economical to choose an autotransformer when the transformation ratio is close to 1. Under the same transportation conditions, the capacity of the autotransformer of the same size can be larger than that of the double-winding transformer. Of course, if electrical isolation, equipment and operation safety are required, the use of autotransformers is not considered.

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