All-Aluminum Alloy Conductive Cross Arm Technology

All-Aluminum Alloy Conductive Cross Arm Technology

The production of ladle refining furnace consumes a lot of electricity. The conductive cross arm, as a bridge for connecting cables to electrodes, has an important impact on the power consumption of the system. It supplies power to the electrodes to heat up the molten steel.

The design of the conductive cross arm should meet the following requirements: light weight, good rigidity, low impedance, and long life.

One end of the electrode cross arm is supported on the lifting column, while the other end clamps the electrode. If the weight of the conductive cross arm can be reduced, the power to drive the electrode column to lift and lower can be reduced, and the response ability of the electrode adjustment controller can also be greatly improved.

1. Current status of the development of the conductive cross arm

During the steelmaking process of the ladle refining furnace, the three-phase electrodes are short-circuited and discharged to form a high-power high-temperature arc between the molten steel, which causes the electrode cross arm to vibrate strongly electromagnetically, so the conductive cross arm should have good stability and strength.

In order to quickly melt the charge, the electrode cross arm should also have a low impedance value. Moreover, in order to adapt to the high-temperature working environment on site, the conductive cross arm is generally cooled by a water cooling system, and the electrostatic dust ignition is reduced as much as possible to extend the working life of the cross arm.

At present, the old conductive cross arm with conductive tube conduction has been basically eliminated and is rarely used due to its complex maintenance.

In the past few years, foreign countries have developed a conductive cross arm made of copper-clad steel plate. Compared with the traditional all-steel conductive cross arm, the conductive cross arm has a better use effect, and the electrical performance of the short-grid system has been improved to a certain extent. However, it also has some shortcomings, such as excessive weight. It is about 20% heavier than the traditional conductive cross arm, which is bound to affect the working sensitivity of the electrode regulator.

In addition, each phase electrode cross arm is an independent monomer, and each phase has some differences in structure. When the electrode holder is damaged, the entire electrode cross arm needs to be taken offline for processing, resulting in a long maintenance cycle, which seriously affects the continuity of steel plant production.

2. Analysis & comparison of three conductive cross arms

The all-steel electrode cross arm consists of two parts: support and conduction, namely steel structure support and conductive tube. Since steel has a high specific gravity and poor electrical conductivity, the disadvantages of this cross arm are heavy weight, high power consumption, short life and poor maintenance. In order to meet its electrical conductivity and safety conditions, the all-steel electrode cross arm has a complex busbar connection process, a long time and poor maintainability.

In addition, due to the strong electromagnetic vibration of the conductive cross arm during the heating process, the maintenance workload of the copper tube increases.

As an upgraded product of the all-steel conductive cross arm, the copper-steel composite electrode cross arm uses the copper plate on the outer layer of the cross arm to conduct electricity, thereby eliminating the conductive steel pipe or copper pipe of the electrode cross arm system, and integrating the conductive and supporting functions of the conductive cross arm. This design can reduce the impedance value of the conductive cross arm and significantly improve the conductive performance.

Its disadvantage is that the copper plate in the copper-steel composite plate is relatively thin, and the conductive area is inevitably insufficient, so there is still room for improvement in the impedance value. The all-aluminum alloy conductive cross arm is a box-type structure made of aluminum alloy plates welded together, and it is cooled by water inside. This structure not only has good rigidity and strength, but also has a light weight.

Since the frequency of system resonance is proportional to the sensitivity of the electrode regulator, reducing weight means improving the sensitivity of the controller, and at the same time greatly improving the sensitivity of the electrode column. The maximum speed of electrode lifting can reach 15m/min, and the speed of electrode lifting and lowering has been accelerated. The imbalance of three-phase current is greatly reduced, which can reduce electrode loss, improve efficiency and save costs.

3. Feasibility analysis of the transformation of the all-aluminum alloy conductive cross arm

After the transformation, the original short network and water-cooling cable remain unchanged, and the upgraded copper-steel composite conductive cross arm and clamp can continue to be used as spare parts for other electric furnaces. The lifting column is slightly adjusted, and the original hydraulic system is not changed. The benefits created after the transformation can be calculated as follows:

(1) Regarding the benefits of power saving

Compared with the copper-steel composite conductive cross arm, the aluminum conductive cross arm can save 3-5% of power[4] and save 4% of electrode consumption. Taking Bengang's 5#LF furnace as an example, the 5#LF furnace has an average annual output of 12,000 furnaces, an average power-on time of 13 minutes, an average molten steel weight of 165 tons, and an average active power of 17M watts/hour.

The average power consumption per ton of steel is (17×1000×13/60)/165=22.32 degrees.

12000×165×22.32×0.03=1325808 kWh of electricity can be saved every year.

At 0.56 yuan per kWh, 1325808×0.56=742,452 yuan can be saved every year.

(2) Regarding saving electrode consumption, the following calculation is made:

When heating, the electrode consumption is calculated as 0.01kg/kwh, and the annual electrode consumption is 12000×165×22.32×0.01=441936 kg.

The unit price of the electrode is 17.41 yuan/kg, and the annual saving is =441936×17.41×0.04=307,800 yuan.

Saving electricity and saving electrodes can save at least 742,452+307,800=1050,252 yuan every year. Conservatively estimated to recover the investment cost in three years, the transformation is completely feasible.

4. Conclusion

Since the success of the all-aluminum alloy conductive cross arm technology in Germany, due to the significant advantages of this technology, countries such as the United States, the United Kingdom and France have successively adopted this new conductive cross arm.

After my country's Baosteel Group built a 300-ton ladle refining furnace using the all-aluminum alloy conductive cross arm technology for the first time in 1999, other domestic steel mills have also targeted the latest developments in this technology field, either to carry out transformation or to introduce technology. It is believed that with the severe energy-saving situation in the domestic steel industry, in the near future, the transformation of the all-aluminum alloy conductive cross arm will have a broader application prospect and become a new trend in the development of electric furnace energy-saving technology.