An autotransformer is a transformer whose windings are primary and secondary on the same winding. According to the structure, it can also be divided into adjustable voltage type and fixed type. The coupling of autotransformer means electromagnetic coupling. Ordinary transformers transfer energy through electromagnetic coupling of primary and secondary coils. There is no direct electrical connection between the primary and secondary sides. The primary and secondary sides of autotransformers have direct electrical connection, and its low-voltage coil is part of the high-voltage coil. Autotransformers and other protective equipment are also used in the protection equipment of communication lines.
An autotransformer is a self-coupling transformer. The autotransformer structure is relatively simple, low cost, and the input/output and 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 two coils coming out of a line. The two coils use the difference of the current to cut the magnetic lines of force to transform the voltage. It is generally used in the boost of DC power. The output and input of the transformer have direct electrical connection, and the safety performance is poor.
Isolation transformer refers to a transformer with electrical isolation between the input winding and the output winding. Isolation transformer is used to avoid accidental contact with live objects at the same time. The isolation of the transformer is to isolate the current of the primary and secondary windings. It was used in the power industry in European countries in the early days, and is widely used in the control power supply of general circuits in the electronics industry or industrial and mining enterprises, machine tools and mechanical equipment, and the power supply of safety lighting and indicator lights.
The main function of the isolation transformer is to isolate the electrical equipment from the power grid. It is 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, it can also electrically isolate the input winding and the output winding from each other, and isolate the input/output and the neutral line to avoid the danger of touching the live object (or metal parts that may be charged due to insulation damage) and the ground at the same time. In addition, the isolation transformer also has a certain effect of suppressing various interferences, has filtering performance, and is highly safe.
Isolation transformer is the most common transformer. Its low-voltage and high-voltage windings are wound by separate coils and have no electrical connection. There is no direct electrical connection between the primary and secondary sides, and the secondary winding is not connected to the ground.
The primary and secondary sides of the autotransformer have direct electrical connection. Its low-voltage coil is part of the high-voltage coil, that is, a winding with only one electrical path. There is a tap in the middle of the winding as the common point of the high-voltage and low-voltage coils.
Usually, one line of the AC power supply voltage we use is connected to the ground, and the other line has a potential difference of 220V or 380V with the ground. People will get electric shock if they touch it. 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 of its lines and the ground. People will not get electric shock if they touch any line, which is safer. Therefore, no matter whether the secondary voltage exceeds the safe voltage value, as long as the person does not touch the two output points of the secondary with voltage difference at the same time, it will not cause harm to people. This is the biggest advantage of the isolation transformer. But it is large in size and high in cost.
Because the high and low voltage coils of the autotransformer overlap, some coil wire materials are saved, which is not only small in size but also low in cost. However, 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 its two windings have a common part, the primary high voltage will “sneak into” the secondary coil, which is very easy to cause harm to people.
Three-phase isolation transformers are mainly used for power loads of power systems and industrial and mining enterprises, and power sources that require isolation from the power grid to convert the mains electricity into magnetic electricity. They are used as power equipment for precision measurement and test purification (anti-interference) of power and power grid. Isolation transformers are safe power supplies and are generally used for machine maintenance to protect, prevent lightning, and filter.
The primary and secondary sides of the autotransformer are directly connected electrically. If the line is damaged or leaking, it is very easy to cause harm to people. It is generally used in places where safety requirements are not high. It only needs to change the voltage so that the voltage meets the required voltage of the equipment. However, the equipment cannot be equipped with a leakage protection device and the neutral wire cannot be grounded.
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