Introduction to Water-Cooled Cables for Submerged Arc Furnaces

Introduction to Water-Cooled Cables for Submerged Arc Furnaces

The submerged arc furnaces busbars system of calcium carbide (ferroalloy, industrial silicon)  is in high temperature for a long time and works continuously in a dusty environment. Its main function is to effectively deliver the output power of the transformer to the electrodes of the electric furnace. The short-circuit system structure of the water-cooled cable of the submerged arc furnace is more compact and electrical, which reduces the layout and arrangement of the circulating cooling water pipeline of the electric furnace, reduces the number of vulnerable parts, and is simple and convenient for maintenance.

On the premise of meeting the production process of the product, how to reduce the impedance of the short-circuit system, improve the utilization rate of electric energy, reduce the amount of precious metal materials and the failure parking rate to achieve a comprehensive increase in economic benefits is a topic explored by engineering and technical personnel in the scientific research and design departments of ferroalloy calcium carbide production.

This article makes some superficial introductions to the structural characteristics and localization process of large-section water-cooled cables in short-circuit systems.

1. Structural Characteristics of Imported Water-cooled Cables for Submerged Arc Furnaces

In the 1970s, my country began to use water-cooled cables on steelmaking equipment such as electric arc furnaces and industrial frequency induction furnaces. The use of water-cooled cables on calcium carbide (ferroalloy) submerged arc furnace systems is the product of digesting and absorbing foreign experience in recent years.

Large-capacity electric furnaces have 12 to 20 cables per phase. Each water-cooled cable is twisted from 0.9 mm diameter pure copper wire into four strands of 22 mm diameter copper stranded cables. Its effective cross-section is about 1200 to 1400 square millimeters.

The four strands of copper stranded cables are separated by insulating tubes to avoid friction between each other, so that the connection between the copper stranded wire and the cable connector is in good contact. The disadvantages that may be caused by welding methods are avoided. There is also a layer of rubber hose containing glass fiber on the outer layer of the bare copper wire. It can withstand high temperatures of about 300 degrees Celsius and ensure good insulation strength.

At both ends of the cable, anti-magnetic stainless steel clamps are used to tighten the cooling water through the evacuation holes on the cable connector to evenly inject the cable into the interior of the cable so that each single copper core wire is fully cooled.

2. Structural Characteristics of Domestic Water-cooled Cables

The water-cooled cable joint connection method currently used in China is mostly plate-type plane connection. This connection method has the characteristics of good conductivity, strong cooling water sealing, and simple installation and debugging. It is a good connection structure. The material, processing accuracy, mechanical strength and assembly level of the sealing ring in the joint are the key factors affecting the conductivity of the water-cooled cable and whether the cooling water can be sealed.

After observing and summarizing the operation of the water-cooled cable, it is concluded that the use of large-section water-cooled cables in the short-grid system of calcium carbide (ferroalloy) ore-heating furnace has the following advantages:

2.1 Due to the good water cooling effect of the water-cooled cable, the current density of the cable reaches about 4A/, which is nearly doubled compared to the allowable current density of the bare soft cable. At the same time, the arrangement rules of the water-cooled cable are reasonable, so it can reduce and reduce the skin effect and self-mutual inductance coefficient in the short-grid system.

2.2 Due to the large allowable current density of the water-cooled cable, the amount of non-ferrous metal copper in the short-grid system is relatively reduced by half, which reduces the investment cost.

2.3 The short-circuit system structure using water-cooled cables is more compact and electrical, reducing the layout and arrangement of the circulating cooling water pipeline of the electric furnace, reducing the vulnerable parts, and making maintenance simple and convenient.

2.4 After using water-cooled cables, the short-circuit failure of the electric furnace is significantly reduced. The short-circuit system failure causes the entire electric furnace to be shut down for about 70% compared with other short-circuit configurations, reducing the maintenance hours and maintenance costs. The furnace can maximize its output.

3 Improvements in Structural Materials

3.1 According to the water quality and water pressure conditions in various places, the diameter of the cooling water diffusion hole on the cable connector is appropriately customized to improve the water cooling effect. Especially when the water pressure is high and overloaded, the cable cooling effect is more ideal, ensuring that the short-circuit system has good power supply quality and maximizes the rational use of electric energy.

3.2 Because the lower water-cooled cable is connected to the electrode copper tile and the electrode conductive copper tube in the high-temperature area near the furnace cover. Under abnormal furnace conditions, furnace gas may burn on the rubber surface of the outer layer of the water-cooled cable, which may cause direct damage to the cable or accelerate the aging and cracking of the rubber. Therefore, a new heat-resistant coating is applied to the outer layer of the rubber sleeve to increase the heat resistance of the rubber sleeve from the original 200 degrees to about 350 degrees, ensuring the insulation and strength of the outer layer of the water-cooled cable and improving the service life of the water-cooled cable. The conductive copper pipe joints designed by foreign imports are made of lead brass except for the sealing ring made of pure copper. The conductivity of this material is far inferior to that of pure copper.

The contact resistance of the two materials is much greater than that of pure copper, which is easy to cause arcing and burning. The H96 copper alloy material J currently used in my country has a low contact resistance of the two material parts under the premise of ensuring the strength requirements of the connecting parts, which greatly improves the conductivity.

4 Characteristics and Precautions of the Use of Water-cooled Cables for Submerged Arc Furnaces

4.1 Scope of Use and Advantages

This product can meet the needs of the secondary current carrying capacity of transformers of different capacities. Its scale can be selected from any grade from 300 to 30,000 square millimeters. The connection form is divided into plate type and tube type. (Special design is also available) has the following advantages:

① The rubber jacket coated with high temperature flame retardant paint has a long-term operating environment temperature of ≤ 350℃℃, and can be burned under flames for a short time when the furnace gas is positive pressure.

② The operating environment temperature of the stainless steel bellows jacket is allowed to be <500C, which is fire-resistant.

③ The cable core is hollow and fired to reduce the skin effect, improving the short-network reactive power consumption.

④ Due to circulating water cooling, the current carrying capacity per unit area of the material can be increased by 4.SA/square millimeter. Compared with the naked cable body, its allowable current carrying density is smaller, saving materials.

4.2 Precautions

① Ensure water pressure and flow during operation

② The current density is not more than 4 5A/square millimeter

③ If there are special requirements, you need to contact the supplier, make detailed calculations for special design, modification and customization, and cannot be applied.