Function of Power Transformer_ Selection Principle of Power Transformer
What is a power transformerPower transformer is a kind of soft magnetic electromagnetic component. Its function is power transmission, voltage conversion and insulation isolation. It is widely used in power supply technology and power electronics technology. According to the transmission power, the power transformer can be divided into several grades: above 10KVA is high power, 10KVA 0.5kva is medium power, 0.5kva 25VA is low power, and below 25VA is micro power. The design of power transformer is different with different transmission power, which should be self-evident.Function of power transformer
For the transformer, it is actually a device that can convert voltage. We usually call it a power transformer. But the difference between switching power transformer and other transformers is that it has one more switch tube than ordinary transformer. In this way, a self-excited intermittent oscillator is formed. Its function is to adjust the input DC voltage into high-frequency pulse voltage and then output.In addition to the above functions, this product also plays a more important role, that is, the transmission and conversion of energy. Generally, in the flyback circuit, when we turn on the switch, the corresponding transformer will convert electric energy into magnetic field and store it. When we turn off the switch, on the contrary, the magnetic field will be converted into electric energy.Power transformer is often used in some electronic products. Its principle is simple, but the winding process of transformer will also have different requirements according to different application occasions (different uses). Although it is only one of the transformers, it is a transformer widely used in life. This transformer can be divided into four categories according to its purpose.
1. Step down transformer: step down transformer is a transformer that converts the high voltage at the input into low voltage.2. Step up transformer: the step-up transformer is a transformer that converts the low value alternating voltage into another high value alternating voltage with the same frequency.3. Isolation transformer: it can be understood literally that separating voltage means isolating strong current or weak current in application.
4. Multi winding transformer: multi winding transformer has several independent secondary windings, and the secondary voltage is different. It can be lower than the primary voltage or equal to or higher than the primary voltage.Selection principle of power transformer for frequency converter(1) Selection purpose. If the grid voltage is not the quantity level required by the frequency converter, the high-voltage power supply can be converted to the voltage level required by the general frequency converter by using the power transformer.
Even if the grid voltage is the quantity level required by the frequency converter, in order to reduce the impact of the frequency converter on the grid, the power can be isolated by adding a transformer, and the input voltage and output voltage of the isolation transformer are the same.(2) Method for determining the capacity of power transformer. The input current of the frequency converter contains a certain amount of high-order harmonics, which reduces the power factor at the power side. If the operation efficiency of the frequency converter is considered, the capacity of the transformer is usually considered according to the following formula:Capacity of transformer (kV · a) = (output power of frequency converter / input power factor of frequency converter) Frequency converter efficiency
Where, the power factor of the frequency converter is 0.8 0.85 when there is input AC reactor Al, and 0.6 0.8 when there is no input reactor al; The efficiency of frequency converter can be taken as 0.95; The output power of the frequency converter shall be the total power of the connected motor.
