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What is the difference between autotransformer and isolation transformer?

Introduction of Autotransformer
Autotransformer refers to a transformer whose primary and secondary windings are on the same winding. According to the structure, it can be subdivided into adjustable pressure type and fixed type. 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. The primary and secondary sides of the autotransformer have direct electrical connections. Its low-voltage coils It is part of the high voltage coil. Protective equipment such as autotransformers are also used in protective equipment for communication lines.
The autotransformer is a self-coupling transformer. The autotransformer has a relatively simple structure and low cost. The input/output and the neutral line are shared. The secondary side of the transformer is part of the primary side. The primary and secondary sides share a winding, like one The two coils that come out of the wire, the two coils use the difference between the large and small currents to cut the magnetic lines to transform the voltage. It is generally used in the boost of DC power. The output and input of the transformer are directly electrically connected, and the safety performance difference.

Introduction of isolation transformer
Isolation transformer refers to a transformer with electrical isolation between the input winding and the output winding. The isolation transformer is used to avoid accidentally touching the charged body at the same time. The isolation of the transformer is to isolate the respective currents of the primary and secondary windings. In the early days, it was used in the power industry in European countries, and it was widely used in the electronics industry or industrial and mining enterprises, machine tools and mechanical equipment in general circuit control power, safety lighting and indicator lights.
The main function of the isolation transformer is to isolate the electrical equipment from the grid. Used in safety occasions or occasions with anti-interference requirements. There is no direct electrical connection between the electrical equipment and the power supply. The isolation structure has many materials and high cost. In addition to changing the voltage, the input winding and output winding can be electrically isolated from each other, and the input/output and neutral line can be isolated to avoid touching the charged body at the same time (or due to insulation damage) Metal parts that may be charged) and the ground. In addition, the isolation transformer also has a certain effect of suppressing various interferences, with filtering performance and high safety.

The difference between autotransformer and isolation transformer
1. The difference in structure
Isolation transformer is one of the most common transformers. Its low-voltage and high-voltage winding are wound by separate coils and are not electrically connected. The primary and secondary sides have no direct electrical connection, and the secondary winding are not connected to the earth. .
The primary side and the secondary side of the autotransformer have a direct electrical connection. Its low-voltage coil is a part of the high-voltage coil, that is, a winding with only one electrical passage, and a tap in the middle of the winding serves as the common point of the high-voltage and low-voltage coils.

2. The difference in safety factor
Usually, one wire of the AC power supply voltage we use is connected to the earth, and the other wire has a potential difference of 220V or 380V between the earth. Human contact can cause electric shock. The secondary high and low voltage coils of the isolation transformer are electrically insulated from each other and are not connected to the ground. There is no potential difference between any two wires of the isolation transformer and the ground. People will not get an electric shock if they touch any line, so it is safer. Therefore, no matter whether the secondary voltage exceeds the safe voltage value, as long as the human body does not touch the two output points of the secondary at the same time, it will not cause harm to people. This is the advantage of the isolation transformer. But the volume is large and the cost is high.

The autotransformer saves part of the coil wire material because the high and low voltage coils have overlapping parts, which is not only small in size and low in cost. But its high and low voltage coils are connected, even if the output voltage of the low voltage side of the step-down transformer is very low, because the two windings have a common part, the high voltage of the primary will also "flee" into the coil of the secondary, which is very easy for people. hurt.

3. The difference in use
Three-phase isolation transformers are mainly used in power systems, power loads of industrial and mining enterprises, and the power supply that requires isolation from the power grid is magnetoelectric, which is used as a power device for precision measurement and test purification (anti-interference) power supply and power grid. Isolation transformers are safe power supplies and are generally used for machine maintenance to protect, prevent lightning, and filter.

The primary side and the secondary side of the autotransformer are directly connected to each other. If the line is damaged or leakage, it is very easy to cause harm to people. Generally used in places with low safety requirements, only the voltage needs to be changed to make the voltage meet the demand voltage of the equipment, but the equipment cannot be equipped with a leakage protection device, and the neutral line cannot be grounded.

The working principle of autotransformer and isolation transformer
Autotransformer (Three Phase)

Isolation Transformer (Three Phase)