Resistance furnaces and salt bath furnaces used for heating of mechanical parts, heat treatment, powder metallurgy sintering, non-ferrous metal smelting, etc. Because the resistance of the heating element is too small, or the resistance of the heating element changes too much during the heating process, a resistance furnace transformer needs to be equipped between the furnace and the power grid to reduce and adjust the input voltage of the electric furnace.
Small-capacity, low-voltage resistance furnace transformers and salt bath furnace transformers are mostly dry-type transformers with boxes and natural cooling; resistance furnace transformers with medium capacity (hundreds to thousands of volt-amperes) are mostly oil-immersed self-cooling transformers. ; Large-capacity ones are forced oil circulation water-cooled transformers.
Working principle of electric furnace transformer
The electric furnace transformer is the power transformer of the steelmaking electric arc furnace. The capacity of the electric furnace transformer is configured according to the size of the electric arc furnace and the smelting process. It meets the requirements of the smelting process through pressure regulation. The voltage regulation methods are divided into two types: on-load voltage regulation and non-excitation voltage regulation. Large-scale electric furnace transformers with on-load voltage regulation do not have series reactors, and small and medium-sized electric furnace transformers without excitation voltage regulation can be divided into two types: those with series reactors and those without reactors. These two structures can operate at the highest Impedance changes between voltages. The former relies on the input and removal of series reactors to change the impedance. The latter changes the winding impedance by changing the connection method of the high-voltage winding of the electric furnace transformer itself. Special transformer for powering electric arc furnaces used for steel smelting. It has large capacity, complex structure and high technical requirements. The secondary voltage is low, generally from tens of volts to hundreds of volts, and is required to be adjusted within a wide range; the secondary current often reaches thousands to tens of thousands of amperes. In addition, in steel smelting, high power is required during the melting period, and the transformer is required to have a 20% overload capacity within 2 hours. During the steelmaking process, the collapse of the charge can easily cause an electrode short circuit, so the primary side of the electric arc furnace transformer should be connected in series with a current-limiting reactor or have a larger impedance to limit the short-circuit current.
The difference between electric furnace transformer and ordinary transformer
1. Different overload capacity requirements.
2. Different short circuit resistance capabilities.
3. The power supply transformer is also required to adjust the voltage during operation.
An ordinary transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are primary coil, secondary coil and iron core (magnetic core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer), etc. According to the purpose, it can be divided into: power transformers and special transformers (electric furnace transformers, rectifier transformers, power frequency test transformers, voltage regulators, mining transformers, audio transformers, medium frequency transformers, high frequency transformers, impact transformers, instrument transformers, electronic transformers , reactor, transformer, etc.). Circuit symbols often use T as the beginning of the number. Example: T01, T201, etc.
The function of electric furnace transformer
In the metallurgical industry, electric furnaces are used to smelt high-quality alloy steel, ferroalloys, etc.;
In the chemical industry, electric furnaces are used to produce yellow phosphorus, calcium carbide, synthetic resins, etc.;
In the machinery industry, electric furnaces are used for the smelting of cast steel and cast iron.