Basic knowledge of rectifier transformer

Modern industrial enterprises generally use DC power supply. In the metallurgical industry, non-ferrous aluminum, magnesium, zinc smelting and electrolytic copper production, in the chemical industry, electrolysis, plating, reagent and chemical production, in the mining machinery, iron and steel industry and transportation drive, cranes, rolling machines, electric locomotives, electric trains and urban traffic trams need DC power, then you need to use rectifier transformers. Follow Suttons Satons to learn about rectifier transformers.

1. What is a rectifier transformer?

The rectifier transformer is the power transformer of the rectifier element, and its task is to change the alternating current into direct current together with the rectifier element. The characteristic of the rectifier device is that the primary input AC, and the secondary output DC through the rectifier element. Converter is the general name of three working modes of rectification, countercurrent and frequency conversion, and rectification is one of them commonly used. A transformer used as a power source for a rectifier device is called a rectifier transformer. Most of the DC power supply for industrial use is obtained from the AC power network through the rectifier transformer and rectifier equipment.

2, classification of rectifier transformer

According to the classification of use, rectifier transformers are divided into metallurgical, chemical and traction three categories. They are different in voltage regulation mode, voltage regulation range and secondary side phase voltage, and the common characteristics are low secondary current and high current. In order to improve the efficiency of rectification, the number of phases on the secondary side is generally no less than three phases, and sometimes six phases, twelve phases or a phase-shifting coil is used.

3, the principle of rectifier transformer

Rectifier transformer is step-down transformer, and then use semiconductor tube rectifier after the required voltage, rectifier transformer and ordinary transformer principle is the same.

Transformer is a kind of equipment that transforms AC voltage according to the principle of electromagnetic induction. Transformers generally have a primary and secondary two mutually independent winding, the two winding share a core. The primary winding of the transformer is connected to the AC power supply, and the alternating current flows through the winding to generate a magnetic potential, so there is an alternating magnetic flux in the closed core. The primary and secondary windings cut the magnetic force lines, and the alternating current of the same frequency can be induced in the secondary. The ratio of turns in the primary and secondary windings of the transformer is equal to the voltage ratio. The primary input voltage is 220V, and the output voltage of 110V can be obtained at the secondary of the transformer. Some transformers can have multiple secondary windings and taps. This allows multiple output voltages to be obtained.

4, the function of the rectifier transformer

1) The role of the rectifier transformer is to connect to the AC/DC power converter to convert the voltage on the power side to the voltage required by the load and provide electrical isolation between the load and the power side;
2) According to ICE-146, circuit 2/8/10/15/19, only one double side winding transformer (coupling group DYN11) is suitable for operation in a 6-pulse rectifier;

3) According to ICE-146, circuit 3/4/5/6/11/12/16/1718, with two transformers with two side windings (connection group DdOy11), electromagnetic decoupling, suitable for operation in a 12-pulse rectifier, on a 12-pulse rectifier, because there are two bridge circuits, so parallel connection, 30 phase shift.

5, the capacity and utilization factor of the whole transformer
The closer the standard capacitance of the rectifier transformer is to the capacity of the DC output, the higher the utilization factor of the transformer. The level of utilization factor depends on the wiring mode of the transformer.

Based on the above, it can be seen that the capacity of the rectifier transformer is related to the connection mode of the rectifier line, and the operation state of the rectifier transformer is different from that of the ordinary transformer, because the current flowing in the secondary coil has a DC child. This situation has influence on leakage flux and additional loss of transformer.

The DC voltage output by the rectifier circuit is not pure DC, and its waveform is pulsating to some extent. In other words, there is an AC component, and obviously the more the number of phases, the smaller the pulse of the DC voltage. Generally, the number of phases in the actual application of the rectifier line does not exceed 12 phases at most. In order to reduce the pulsation of the DC voltage, a filter reactor and a shunt capacitor are connected in series in the rectifier circuit, so that the voltage after rectification can be close to pure DC.

In the three-phase rectifier line, the utilization factor of the secondary coil, the three-phase half wave, K= 0.67, and the six-phase half wave, K= 0.55, are not high, so the industrial rectifier transformer adopts the three-phase bridge type and double Y-balanced reactor rectifier line.