Electric furnace transformers can be roughly divided into three categories: resistance furnace transformers, electric arc furnace transformers and induction furnace transformers.
Resistance furnace transformers are used for resistance furnaces and salt bath furnaces for mechanical parts heating, heat treatment, powder metallurgy sintering, non-ferrous metal melting, etc. Since the resistance of the heating element is too small, or the resistance of the heating element changes too much during the heating process, it is necessary to equip the furnace and the power grid with a resistance furnace transformer to reduce and adjust the input voltage of the electric furnace. Three-phase resistance furnace transformer. Small-capacity, low-voltage resistance furnace transformers and salt bath furnace transformers are mostly dry-type transformers with case and natural cooling; medium-capacity (hundreds to thousands of volt-ampere) resistance furnace transformers are mostly oil-immersed self-cooling transformers. Large capacity is a forced oil circulating water-cooled transformer.
The electric arc furnace transformer is a special transformer for supplying electric arc furnaces for steel smelting. Large capacity, complex structure and high technical requirements. The secondary side voltage is low, generally from tens of volts to hundreds of volts, and is required to be adjustable over a wide range; the secondary current is often thousands to tens of thousands of amps. In addition, in steel smelting, the melting period requires a large power, and the transformer is required to have a 20% overload capacity within 2 hours. In the steel making process, the electrode is short-circuited due to the collapse of the charge, so the primary side of the arc furnace transformer should be connected to the current limiting reactor or have the impedance of the larger electric furnace transformer to limit the short-circuit current. The electric furnace is also required to regulate the voltage when the electric furnace is running. There are two types of voltage regulation methods for electric furnace transformers. 1 Direct voltage regulation method: On the original winding of the transformer, the tap is connected to the tap changer. △-Y switching can also be used between the primary three phases to achieve secondary voltage regulation. △-Y switching is a very economical voltage regulation method. By reducing the number of primary turns, the secondary voltage can be reduced to 1/. Since there are 9 taps per phase winding, plus △-Y switching, a total of 2 × 9 or 18 voltages can be obtained. 2 Indirect voltage regulation method: The figure shows the indirect voltage regulation method with series transformer. The main transformer 1 is a three-winding transformer (see multi-winding transformer), 1 winding is a high voltage winding, connected to the grid; 2 winding is a tapped winding, connected in series with the primary winding 4 of the series transformer II through a tap changer; It is connected in series with the secondary winding 5 of the series transformer II to supply power to the electric furnace load. By changing the primary voltage of the series transformer II through the tap changer, the voltage output of the 3 and 5 windings can be changed. The 3, 5 windings connected to the load are generally only 1 to 2 turns, usually made of copper or aluminum plates.
The induction furnace transformer is used to melt the induction furnace of black and non-ferrous metals. It is essentially a special Satons electric furnace transformer.
The induction furnace is divided into two types: iron core and iron core. A core induction furnace is a transformer having a core and a short-circuit secondary winding. The primary winding of the transformer is connected to the power supply. The secondary winding is actually only one turn. It is the molten metal contained in the melting tank. When the primary winding is energized, the secondary winding generates an induced current that circulates in the slot, thereby generating heat to melt the metal.