1. Special transformers should be used for medium-frequency induction furnaces

Due to the provisions of power supply policies in my country, the transformers used for industrial electricity are generally S7 and S9 transformers, with a secondary voltage output of 380V. The secondary output voltage of foreign industrial furnaces is 650-780V. It can be seen that if a special transformer dedicated to medium-frequency induction furnaces is used to make the secondary output voltage 650-780, when the output power is constant, the output current is reduced to 0.585 times the original, and the copper loss is reduced to 1/3 of the original. The further reduction of copper loss reduces the heat generated by the transformer, so that the resistance of the copper coil will not increase due to excessive temperature. The cooling system takes away less heat, and the energy-saving effect is significantly increased. In addition, according to needs, the power supply voltage can be adjusted in time during the operation of the furnace to adjust the input power of the furnace, so that the loss of the medium-frequency induction furnace is minimized as much as possible. Therefore, it is imperative to use a special transformer for medium-frequency induction furnaces to increase the voltage.

In addition, limiting the no-load operation of the transformer also plays a certain role in energy saving. In practical applications, when the no-load time exceeds a few hours or production is stopped, the power should be turned off and the transformer should be stopped in time, which is more conducive to energy saving and consumption reduction of the transformer and improving the power factor.

2. Correctly select the capacity of the medium-frequency induction furnace and increase the matching power

The selection of furnace capacity generally mainly considers whether the productivity of the furnace can meet the needs of molten iron. However, for the same amount of molten iron, you can choose a single large-capacity furnace or multiple small-capacity furnaces. This must be analyzed and compared according to actual requirements. In occasions where a large amount of molten iron is only sometimes needed for the production of large castings, it is not appropriate to use a single large-capacity furnace, but multiple furnaces of appropriate capacity should be selected under normal production conditions. In this way, the reliability of the flexibility of the production process can be improved, the problem of shutdown caused by accidents of a single large-capacity medium-frequency induction furnace can be solved, and the power consumption caused by the excessive capacity that cannot reach the rated power when smelting a small amount of molten iron can be reduced.

The capacity of the induction furnace is closely related to the technical and economic indicators of the furnace. Generally speaking, large-capacity furnaces have high technical and economic indexes, because as the furnace capacity increases, the unit energy loss of melting cast iron decreases accordingly. Under the same capacity, the matching power of the medium-frequency induction furnace should be increased to improve the melting efficiency of the furnace and reduce its power consumption.

3. Improvement of induction coil and water cable

The reactive water pump of medium frequency induction furnace is mainly caused by the copper loss of induction coil and electric cable during the operation of the furnace. The unit resistance has a huge impact on the copper loss. At present, in order to reduce costs, some electric furnace manufacturers mostly use cheap and high-resistance copper instead of low-resistance No. 1 electrolytic copper as the raw material of induction coil, which leads to high resistance of induction coil and water cable, and relatively large power loss per unit time.

High-quality high-purity copper tube has bright surface color, low resistivity and good conductivity; while inferior copper is not entirely made of copper material, the copper tube is black and hard, and cannot withstand large current due to many impurities, and the heat generated by electricity is high. The selection of materials should be distinguished.

(1) Increase the cross-section of induction coil and water cable. Copper wires and copper conductor cables with larger cross-sections can not only reduce the heating and voltage loss of wires, but also increase the reliability of distribution lines and adapt to long-term development. In addition, it is also very beneficial from an economic point of view. The increased investment can be recovered quickly, and users can get more benefits in long-term use.

(2) Reduce the working temperature of the induction coil and water cable. When the induction coil and water cable of the induction furnace are heated, the resistivity increases due to the resistance temperature coefficient of copper, the resistance becomes larger, and the power consumption increases. For every 10℃ increase in the working temperature of the coil, the resistance increases by 4%, and the power loss increases by 4%. When the working temperature of the induction coil is reduced from 80℃ to 50℃, the power loss has been reduced by 12%, which is a considerable loss for a medium-frequency induction furnace with a large power. Therefore, an effective cooling system should be used to efficiently reduce the temperature of the power supply line, and try to avoid the vicious cycle of temperature increase-resistance increase-temperature increase, and reduce line loss.

4. Use new scale inhibitors and closed water cooling systems

(1) Scale has a huge impact on the cooling capacity of the cooling system. The impact of scale on the use of copper pipes directly changes the working temperature of copper pipes. The composition analysis of copper scale found that the scale is mainly in the form of insoluble salts and oxide precipitation in the ash water. As the temperature of the cooling water increases, the salts in the water gradually exceed the saturation limit and precipitate to form scale with extremely poor thermal conductivity. Scale deposited on the inner wall of the coil will reduce the water cross-sectional area, block the pipe, increase the water circulation resistance, and hinder normal heat exchange. Since the thermal conductivity of scale is only 0.464-0.8W/m·K), which is much smaller than the thermal conductivity of copper pipe 320W/(m·K), the heat exchange rate is greatly reduced, thus shortening the service life of the equipment. At the same time, the heat flow distribution of copper pipe is different, so the thickness of scale is different in different places. If the scale is too thick at the location where the temperature of the copper pipe is too high, local overheating will occur, thus burning the coil and water cable, and even causing serious safety accidents such as electrical leakage and short circuit.

(2) Use type scale inhibitor

The cooling water of the medium frequency induction furnace circulates in the induction coil and water cable, which contains a large amount of ions. The scale inhibitor produced by some existing methods has no obvious effect on cooling water scale inhibition. For example, the magnetization treatment method is greatly affected by the magnet's properties, and the scale inhibition effect is unstable; the electrostatic treatment has no obvious effect on the crystallization and precipitation of calcium and magnesium salts in water, and the power devices of such equipment are in direct contact with water, so that high-frequency pulse voltage is generated in the middle, which has a strong demagnetization effect on the permanent magnet and reduces the scale inhibition effect; the chemical reagent method is easy to cause water quality changes, and the scale inhibition effect is greatly reduced due to the electric angle effect of the electric potential in the water; the electrostatic field method and the sound method also reduce the scale inhibition effect due to the interference of the electric potential in the water.

For this reason, a new type of scale inhibitor is developed, which uses several electrodes to balance the capacitor group. The charged cooling water passes through the capacitor group to generate an electric potential, and the coil is connected to the capacitor to form resonance. The parallel resonant circuit increases the voltage of the electrode. The coil also short-circuits the intermediate frequency component to form a Faraday cage, reduces the DC potential difference, and has a scale inhibition effect on metals such as copper and iron. The electric potential generated on the metal electrode produces a Lofert force and thermal effect on the scale deposits in the water, thereby loosening and refining the scale crystals, making them suspended in the water and discharged regularly, so as to inhibit crystallization and prevent scale formation. Using chromium zinc as an electrode can prevent copper and iron from rusting. The use results show that the scale inhibitor of the newly opened equipment has a good scale prevention effect and only needs to be cleaned once a year, which greatly reduces the generation of scale and greatly extends the service life of the sensor and water cable.

(3) Use a closed circulation cooling system. The sensor cooling water should be clean and free of impurities, with a solid content of no more than 10 mg/L, and the resistivity of the water should be greater than 2.5×103·cm. Since the water with high hardness contains a large amount of insoluble salts, it is easy to precipitate and form scale. Therefore, the cooling water should use soft water with low hardness, with a total hardness of no more than 2.8 mg/L and a sulfite and chloride content of no more than 50 mg/L. It is best to use remote distilled water to minimize the probability of scale formation.

A closed-loop cooling water system is used. This system has a two-level circulating water system. The outer loop is an open circulation system, and the inner loop is a closed circulating water system. A water-water heat exchanger is used to transfer heat. The inner loop uses soft water and distilled water, which is convenient for water quality treatment. The system has high reliability, low operating costs, and low requirements for the quality of the external return water. Therefore, the service life of the sensor can be greatly improved.

(4) Strictly control the temperature of the circulating cooling water in the induction coil to achieve the purpose of energy saving and consumption reduction.

The temperature of the circulating cooling water directly affects the working temperature and coil resistance of the coil, and has a considerable impact on the copper loss of the induction furnace. If the inlet and outlet water temperatures are too low, the circulating water cooling will consume a lot of energy and will also take away heat from the furnace body, increasing power consumption; if the water temperature is too high, it will not be conducive to the cooling of the induction coil and increase power consumption. Therefore, choosing a good cooling water temperature is an important link. The inlet and outlet water temperatures of the cooling water should be controlled at a constant temperature. The inlet water temperature is generally 20-30℃, and the outlet water temperature is preferably 50℃.