There are three kinds of power supply for induction furnace: 1. if generator set, 2. SCR static converter, 3. frequency multiplier (1.2 for medium and small induction furnace, 3 for large furnace)
1、 In the SCR static converter circuit, the three-phase power frequency power is supplied to the inverter after the transformer depressurizes. In the converter, the three-phase bridge half control full wave rectification is first conducted, and then the DC power is obtained through reactor filtering. The DC power is transformed into the frequency variable medium frequency power supply through single-phase bridge inverter and supplied to the induction furnace.
2、 The main circuit of if generator set consists of inductor, capacitor, if generator set and high (low) voltage switch. The intermediate frequency generator set is composed of generator and motor. The working voltage of the motor can be divided into two types: high voltage (6000V or 10000v) and low voltage (380V). High pressure is used for large capacity furnace and low pressure is used for small capacity furnace. The motors are squirrel cage asynchronous motors. The generator is driven by the motor and generates intermediate frequency current to supply to the induction furnace.
If generator sets are divided into horizontal and vertical. The frequency of output current of if generator set does not change with load, it has the advantages of strong overload capacity, reliable operation, convenient installation and maintenance. However, compared with static frequency converter, it has many disadvantages, such as noise, vibration, heavy material, bulky volume and low electrical efficiency (80-85%.
A. Rectification: three phase AC (380V) is rectified to DC through three-phase bridge full wave rectifier line
B. Filter: after the reactor filter, a stable DC power supply is obtained to supply the inverter.
C. Inverter: the filtered DC is made of single-phase bridge inverter line, which uses the turn on and off of SCR to make DC current into frequency adjustable intermediate frequency current. SCR static converter is superior to if generator group, but there are still problems that the quality of the components is required to be high. For example, the switching parameters of thyristor used in parallel in inverter must be as close as possible, and higher maintenance technology is required.
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