Electric arc furnace water heater cable

Electric arc furnace water heater cable

 

Water-cooled cables of electric arc furnaces deliver the supply power to the electrodes. This power flows through the twisted conductors of the cable and the heat produced by the high electric current is mitigated by the water passing the cable’s water channel. In contrary to the induction furnaces with plenty of manufacturers throughout the world and considering limited design and manufacturing resources for the electric arc furnaces, applied water-cooled cables do not cover a wast variety of design sketches. Below illustration shows a water-cooled cable applied to a induction furnace:

Cable Terminal

Electric arc furnaces’ water-cooled cable’s terminals are manufactured in two ways:

• similar to water-cooled cables of induction furnaces, they are machined out of the solid copper rods, usually up to diameter of 40 Inches.
• Or mainly, they are casted from molten copper in the proper matrix, then forged and machined.

Using welding methods and so on is not suggested for manufacturing the arc furnaces cables’ terminal.

It should be noted that the copper grade here is ETP under ASTM-C11000 standard.

In the design process of arc furnaces cables’ terminal, electric current density is so important to consider which, for desired operation, can be chosen 0.7 A/mm2 in the contacting surface.

Generally, these kind of cables are manufactured with a fixed and a moving terminals to avoid extra tension if the ends are not in the same level or aligned.

Manufacturing of the moving terminal has an important and sensitive significance, according to water isolation and the quality of the moving fittings.

bolts connecting terminals

It is suggested that bolts connecting terminals to the power source and electrodes fittings, be of stainless-steel with grade of 304 (A2) soaked in grease (preferably a conducting type). Also it is worth noting that the bolts and fittings should be fixed similarly by a torque-meter. As the main sizes for these bolts are 16, 20 and 22, below table contains standard torque for fastening the bolts in both dry and greased ways:

Connector for connecting terminals to internal twisted conductors

Araz Trans Co. applies heavy press technology to arc furnace cables’ terminals. This method completely fills pores between the terminal and internal conductor turning them into an integrated part. Applying soldering and welding is not suggested by this company according to high electric currents.

Internal twisted conductors

To reach thorough information on this topic, please refer to the “twisted copper conductors” section.

Hose

To reach thorough information on this topic, please refer to the “free crane hoses” section.

Cable Protection

Against the cables of induction furnaces, which may benefit fireproof wrapping (if needed), water-cooled cables of arc furnaces need more protection to alter operation reliability. The protection for these cables are:

• Protecting the hose against high temperatures: In order to protect the hose against melt splash, while electrodes enter and exit the crucible, the simple fireproof wrapping is not adequate. Hence, Araz Trans Co. applies the special Pyroblanket cover of flameproof grade. This product, made out of woven fiberglass and silicon resin, can bear constant heat up to 260 C and transient heat up to 1700 C. Alongside desirable thermal and physical characteristics, simple substitution process without needing to disconnect it from the furnace is a great advantage. It is fastened to the hose by hook-and-loop (Velcro) system.

• Protecting the cable against rubbing friction and strokes: Active and moving state of electric arc furnace cables because of electrodes constant movements, results in contacts and rubbing to each other and establishments around. Then, to protect them against the aforementioned issues, special bumpers are applied made out of natural rubber installed in both moving and fixed forms. Fixed ones which are vocalnized to the hose firmly, are fixed with steel fasteners, while moving ones (also called free bumpers) are placed freely around the hose and can be moved by operator. It is noteworthy to tell that moving bumpers can move around by cable moving or vibrating.

• Protecting the cable against bending: One of the most important issues in exploiting water-cooled cables of electric arc furnaces is tension and bending level caused by constant movements. To be more precise, having fixed terminal connected to the power supply firmly and the other terminal connected to the electrode, results in tension and bending specially near the terminals. This problem may lead in extra tension on internal conductors and possible disconnection of some of the conductors.According to the standards about applying water-cooled cables, bending radius for hanging part of the cable and fixed part is 5 and 6 times of the terminal diameter, respectively.

Electrical resistance of the cable

Power loss of the cables are in direct relation to the electrical resistance of their conductors. In the case of the electric arc furnaces power loss gains more importance due to the high current passing through the cable. On the other hand, as time passing, some strings of the conductor may be depricated by the chemical erosion or phisical strokes and torn. This would lead in none-usable state of the cable.

One good measure to determine the deprication level of the cable is to regularly inspect the electric resistance of the cable in predefined time intervals. Because torn strings means reduced cross-section and increased electric resistance. Acceptable value for measured resistance is 1.5 times greater than its initial resistance. Hence, in order to have a good citerion, cable’s initial electric resistance should be determined.

As the electric resistance for water-cooled cables of the electric arc furnaces is a matter of micro ohm, then a micro ohm meter must be used.

The following relationships show how to calculate the electrical resistance of a new cable (before first use) and the amount of cable loss:

The water enters the cable through the fixed terminal and flows toward the moving terminal in two parallel passes. One of these passes is the central duct and the other one is the space encircled between the conductor and the hose.

In order to let the water pass in the central direction a water canal is considered along the cable that prevents the conductor of being tied o each other and water flow to be disturbed. Against the water-cooled cables of the induction furnaces where the canal is a simple spring, the central canal for water-cooled cables of the electric arc furnaces are of two different kinds.

 

The first type is a natural rubber extruded in the star shape that fastens the conductors in their place.

 

The other type is a hose or extruded rubber in the pipe form fixed to the cable terminal with a brass fastener.

Aside from the central canal, the terminals of water-cooled cables have side holes for passing water in order to cool down the outer surface of the internal conductors.

Fasteners and fittings

For more information about the Fasteners and fittings of the water-cooled cables, reach out to the section named “connection fasteners”.