Technical Retrofit of Water-Cooled Cables for a Refining Furnace

Abstract

The design and installation method of traditional water-cooled cables used in refining furnaces have significant defects, resulting in a high failure rate and difficult maintenance. Therefore, improvement is urgently required. The old-type water-cooled cable adopts a bundled structure composed of eight water-cooled cables with a diameter of 62 mm twisted around a central water-cooling pipe in a rope-like form. This structure occupies a large volume and provides unsatisfactory cooling performance.

In the retrofit, a copper busbar water-cooled cable connector base is adopted at the transformer side, fastened by bolts and nuts. At the electrode arm side, a copper busbar water-cooled cable connector base is also used and fitted to the T-shaped bracket of the electrode arm, secured with bolts and nuts. The bolts and nuts are insulated using insulating plates, insulating sleeves, and insulating washers.

After modification, cable replacement becomes more convenient, the overall size is reduced, the cooling effect is improved, and the solution is economical and practical.

Keywords: Water-cooled cable; cooling effect; occupied volume; easy disassembly; economical and practical

Introduction

Water-cooled cables are large-cross-section flexible current-carrying conductors used in metallurgical equipment. They mainly consist of an external rubber insulating sheath, flexible conductors, a rubber core pipe, differential springs, stainless steel clamps, brass terminals, protective rings, and thermal protection components [1].

Since water-cooled cables are flexible current carriers, the conductor cross-sectional area must be selected according to requirements, taking into account the geometric mean radius and the minimum bending radius [2]. The geometric mean radius refers to the average radius of the flexible conductor layer in the cable cross-section. The minimum bending radius is the minimum allowable curvature radius when the cable is subjected to external bending force.

Water-cooled cables are mainly used as flexible connections between the short network of an electric arc furnace transformer and the electrode holder arm, providing current to the electrode arm. According to transformer capacity, appropriate cable size, conductor cross-sectional area, current-carrying capacity, rated voltage, cooling water flow, cooling water pressure, minimum bending radius, and length can be selected [3].

1. Introduction to the Old-Style Water-Cooled Cables of the Refining Furnace

The main functions of a refining furnace include degassing, composition adjustment, temperature control, and inclusion removal. Degassing is achieved by vacuum and argon blowing. Composition adjustment is performed through argon stirring, alloy addition, and slag control. Temperature adjustment is achieved through chemical heating, electric arc heating, or induction heating. Inclusions are removed by argon stirring and inclusion modification.

The old ladle refining furnace, built in the 1980s, uses a water-cooled cable design and installation method with serious defects, leading to high failure rates and difficult maintenance. The water-cooled cable adopts a bundled structure consisting of eight 62 mm diameter water-cooled cables twisted around a central cooling pipe in a rope-like form, occupying a large volume.

Each of the eight cables consists of copper flexible conductors, rubber core pipes, brass terminals, stainless steel clamps, and an outer rubber insulation sheath. At the transformer short-network connection, a water-cooled disk is used, consisting of a hollow metal cooling pipe and eight cable sockets arranged around it. A rubber cooling hose is inserted into the metal cooling pipe, and the eight cables are wound around the hose. Their brass terminals are inserted into the eight sockets of the water-cooled disk, forming a rope-like bundle.

The other end of the cable bundle is connected to the electrode arm in the same way, forming the flexible connection between the transformer short network and the electrode arm, supplying current and cooling water to the electrode arm.

2. Significance of the Water-Cooled Cable Retrofit

The old bundled water-cooled cable system has many disadvantages.

Because it consists of a central cooling hose and eight surrounding water-cooled cables, it occupies a large space and provides unsatisfactory cooling performance. Each electrode arm requires two cable bundles, and a refining furnace has three electrode arms, requiring six cable bundles in total — equivalent to 48 water-cooled cables.

The rubber materials of both the central hose and the surrounding cables are prone to aging, fatigue, cracking, and water leakage. Leakage greatly reduces cooling performance, shortens the service life of the cables and electrode arms, and can easily cause thermal shutdowns.

Due to the complex structure of the cable bundle, maintenance requires a large amount of manpower and time.

3. Technical Retrofit of the Refining Furnace Water-Cooled Cables

Because the old water-cooled cable bundles are extremely inconvenient in operation and maintenance, a technical retrofit was carried out.

First, based on transformer power and the operating current and voltage requirements of the refining furnace, a new type of water-cooled cable was selected. After determining the conductor cross-sectional area, the geometric mean radius and minimum bending radius were determined based on the distance between the transformer and electrode arm and the lifting height of the electrode arm.

The connection method between the transformer and electrode arm was modified. At the transformer end, a copper busbar water-cooled cable connector base was adopted and fastened with bolts and nuts. At the electrode arm end, a copper busbar water-cooled cable connector base was also used and fitted to the T-shaped bracket of the electrode arm, secured with bolts and nuts. Insulation of bolts and nuts was achieved using insulating plates, insulating sleeves, and insulating washers.

After modifying the connection method, six new water-cooled cables were installed between the transformer and the electrode arms.

4. Results After the Retrofit

The new water-cooled cable consists of a central cooling water pipe, surrounding conductors, an outer rubber hose, and multiple layers including a shielding layer, insulation layer, and metal outer sheath, forming an integrated cylindrical structure. The cable terminals adopt a flat plate-type connection.

The outer layer of the cable is a sealed and insulated elastic rubber hose. The inner structure is a conductive flexible copper cable, with circulating cooling water between them to eliminate self-heating. Based on local water quality and pressure conditions, the diameter of the cooling water holes in the connectors was customized to improve cooling performance.

Especially under large pressure fluctuations and overload operation, the cooling performance is more ideal. With improved cooling, the current density reaches about 4 A/mm², approximately double that of traditional bare flexible cables.

The retrofit significantly improves cooling performance, reduces maintenance and replacement time, lowers maintenance costs, and effectively reduces thermal shutdown losses.

5. Advantages of the New Water-Cooled Cables

The old refining furnace was built in the 1960s and 1970s, and its design level lags behind that of modern furnaces. The old furnace has three-phase electrode arms, each phase equipped with two cable bundles, and each bundle consists of a large cooling hose and eight water-cooled cables — a total of 48 cables. This results in high spare parts consumption and complicated maintenance, increasing downtime and production losses.

After the retrofit, the advantages include:

1. The original bundled structure is replaced with standard single water-cooled cables with bolted copper terminals, making installation efficient and convenient.

2. The original water-cooled disk connection is replaced by direct surface contact between copper terminals and the transformer/electrode arm connectors, secured with bolts and nuts, saving maintenance time and reducing costs.

   
   

6. Practical Benefits After the Retrofit

Due to rubber aging and friction between cables, the old system is prone to damage and water leakage. In metallurgical operations, water leakage is extremely dangerous, as water vaporizes upon contact with high temperatures, posing serious safety risks to equipment and operators.

The retrofit effectively prevents water leakage accidents and reduces unnecessary losses. Compared with the old system of 48 cables, the new system has lower maintenance costs, simpler maintenance procedures, and shorter repair time.

In metallurgical production, “time is money,” so reducing downtime is critical. The retrofit brings substantial practical and economic benefits to the enterprise.

7 Conclusion

Before the retrofit, the old water-cooled cables adopted a bundled rope-like structure composed of eight 62 mm diameter cables wrapped around a cooling pipe. This design occupied large space, had poor cooling performance, a high failure rate, and was difficult to maintain.

After the retrofit, the bundled structure was replaced with standard single water-cooled cables. The short-network connectors were replaced with easy-to-disassemble copper terminals directly bolted to the transformer and electrode arm connectors. Insulation is ensured using insulating plates, sleeves, and washers.

The retrofit makes cable replacement easier, reduces occupied space, improves cooling performance, and is economical and practical. It effectively reduces downtime caused by equipment failure and maintenance, achieving cost reduction and efficiency improvement for the enterprise.

References

[1] Gou Shunhu, Liu Junzhao, Jian Le, Duan Wangchun, Zhang Ruiqing.
Design of Large-Cross-Section Pre-Bent Water-Cooled Cables.
Mechanical Research and Application, 2015(04).

[2] He Yushan, Xu Yongzhou.
SDL-Type Modular Water-Cooled Cables for Electric Arc Furnaces.
Metallurgical Equipment, 1992(06).

[3] Li Huaiyin.
Analysis of Current Imbalance in Water-Cooled Cables of Submerged Arc Furnace Short Networks.
Ferroalloy, 2009(06).