Submerged arc furnace transformers: The load is continuous and stable, and there is little electrode short circuit.
The impedance voltage is required to be as low as possible, and it is generally required that the furnace transformers can withstand 110% of the rated current for long-term continuous operation.
Technical Requests For Submerged Arc Furnace Transformers As Follows:
(1) Due to the frequent changes of charge resistance, raw materials and power supply voltage, the transformer requires more voltage regulation stages.
The output voltage difference of each stage is small, and almost all require the constant capacity output of the first few stages and the constant current output of the latter stages.
(2) The primary winding of the medium and small three-phase submerged arc furnace transformers can be designed as D connection or Y connection.
And at 5000KVA and above, it is mostly designed for D connection.
However, the first and last ends of the windings should be drawn out from the box cover for Y connection in the oven, and the D connection method is still maintained during normal smelting.
(3) Generally, transformers of submerged arc furnaces of 20000KVA and below are made of three-phase.
The large-scale SAF transformers are mostly in the form of three-phase groups composed of three single-phase submerged arc furnace transformers.
This is because the high-current short-circuit network of the submerged arc furnace transformer has a strong difference in the length of each phase, which makes the three-phase impedance seriously unbalanced, resulting in power transfer and unbalanced current and power of each phase.
The single-phase transformer can be symmetrically distributed around the electric furnace, shorten the length of the short network, and make the three-phase impedance approximately balanced.
It can greatly improve the power transfer and the imbalance of each phase,Thereby reducing the power loss and increasing the power factor of the electric furnace operation.
(4) Since the load imbalance and energy transfer are caused by the short net structure itself, and are difficult to eliminate, the electrodes will appear “live phase” or “dead phase”.
The main condition for the normal operation of the electric furnace is that the power of each phase in the molten pool should be balanced.
To this end, the transformer should have the ability to adjust the voltage of each phase independently, that is, the so-called “split-phase voltage regulation”.
In this case, each phase of the furnace operates at the optimum voltage, the amperage of each phase is balanced, and the power of the molten pool is also balanced.
Although the energy transfer is preserved, the adverse effect of the energy transfer on the furnace operation can be eliminated.
The allowable difference of the output voltage of each phase of the split-phase voltage regulation electric furnace transformer is limited by the circulating current in the primary D-connected winding, and the circulating current is generally not greater than 20% of the rated current.
(5) As the power of the electric furnace increases, the large current loop makes the furnace have a larger reactance value, resulting in a decrease in the power factor of the electric furnace.
Connecting a capacitor to the furnace loop is the most effective way to compensate for no power.
Therefore, in large-scale submerged arc furnace transformers, compensation capacitors are often considered on the tertiary side.
With the above further understanding, when choosing a submerged arc furnace transformers, we will be more aware of the parts that need to be tested and paid attention to, so as to buy a reliable and high-power product.