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Frequently Asked Questions from TANO CABLE

Faq
FAQ
Q
What is Hot-Dip Galvanizing?
A
Hot-dip galvanizing (HDG) is the process of coating fabricated steel by immersing it in a bath of molten zinc. There are three fundamental steps in the hot-dip galvanizing process; surface preparation, galvanizing, and inspection (Figure 1).

(Figure 1)

Surface Preparation

When the fabricated steel arrives at the galvanizing facility, it is hung by wire or placed in a racking system which can be lifted and moved through the process by overhead cranes. The steel then goes through a series of three cleaning steps; degreasing, pickling, and fluxing. Degreasing removes dirt, oil, and organic residues, while the acidic pickling bath will remove mill scale and iron oxide. The final surface preparation step, fluxing, will remove any remaining oxides and coat the steel with a protective layer to prevent any further oxide formation prior to galvanizing. Proper surface preparation is critical, as zinc will not react with unclean steel.
Galvanizing

After surface preparation, the steel is dipped in the molten (830 F) bath of at least 98% zinc. The steel is lowered into the kettle at an angle that allows air to escape from tubular shapes or other pockets, and the zinc to flow into, over, and through the entire piece. While immersed in the kettle, the iron in the steel metallurgically reacts with the zinc to form a series of zinc-iron intermetallic layers and an outer layer of pure zinc.
Inspection

The final step is an inspection of the coating. A very accurate determination of the quality of the coating can be achieved by a visual inspection, as zinc does not react with unclean steel, which would leave an uncoated area on the part. Additionally, a magnetic thickness gauge can be used to verify the coating thickness complies with specification requirements.

(Figure 2)

Coating Benefits

Hot-dip galvanizing provides a number of benefits to the steel it protects. The metallurgically-bonded zinc-iron alloy layers not only create a barrier between the steel and the environment, but also cathodically protect the steel. The cathodic protection offered by zinc means the galvanized coating sacrifices itself to protect the underlying base steel from corrosion.

The tightly adhered coating, which has bond strength of around 3,600 psi, is also extremely abrasion-resistant, as the intermetallic layers are harder than the base steel (Figure 2). However, even if the coating is damaged, zincs sacrificial action will protect exposed steel up to ¼ inch away.

In addition to the cathodic protection offered by hot-dip galvanizing, there are a few other characteristics of the coating which provide longevity. First, reaction in the galvanizing kettle is a diffusion process, which means the coating grows perpendicular to the surface, ensuring all corners and edges have at least equal thickness to flat surfaces. Furthermore, the complete immersion in the zinc bath provides total coverage of the steel, including the interior of hollow structures.

Finally, the zinc coating naturally develops an impervious layer of corrosion products on the surface, know as the zinc patina. The patina, cathodic protection, complete coverage and all of these other features, provide hot-dip galvanized steel with a long, maintenance-free service life. Thjavascript:void(null);e time to first maintenance for hot-dip galvanized steel can be seen in Figure 3.

(Figure 3)
Q
What are the differences between DC and AC?
A
1. Different concepts

AC stands for alternating current, which refers to current whose direction and magnitude change periodically over time. Simply put, alternating current changes direction many times in one cycle.

DC stands for direct current, which refers to current whose direction and magnitude remain constant. The current of direct current flows in only one direction, so its voltage is also constant.

2. Different working principles

The working principle of AC is based on Faraday's law of electromagnetic induction. When a coil rotates in a magnetic field, an induced electromotive force is generated in the conductor, thereby generating alternating current. Since the rotational motion is periodic, the direction of the generated current will also change periodically, which is the characteristic of alternating current. In the power grid, the generator generates alternating current through a rotating magnetic field, and changes the voltage through a transformer, and finally transmits it to the user end.

The working principle of DC is relatively simple. When the power supply provides a constant voltage difference, the current will flow from the positive pole of the power supply to the negative pole in a fixed direction. The battery is the most common DC power supply, which generates a constant current through a chemical reaction. Since the DC current does not change direction, it can be directly used to drive various electrical equipment.

3. Different applications

Typical applications of AC:
Home power grid: Most households use AC power. Electrical appliances such as lighting, air conditioning, and refrigerators all rely on AC power.
Industrial production: Many industrial equipment, such as motors and welding machines, are driven by AC power.
Power transmission: AC power is transmitted to distant users through high-voltage transmission lines, and then stepped down by transformers for users to use.

Typical applications of DC power:
Electronic devices: Most portable electronic devices, such as mobile phones, laptops, tablets, etc., use DC power.
Electrical vehicles: Batteries of electric vehicles and electric bicycles provide DC power to drive motors.
Energy storage system: Photovoltaic panels in solar power generation systems generate DC power, which is stored in batteries and then converted to AC power for home use through inverters.

4. Advantages and disadvantages

Advantages of AC:
Easy to transmit: AC power can be easily stepped up and down by transformers, so that power can be effectively transmitted to long distances.
Mature power generation technology: AC power generation technology is relatively mature, with low cost, and suitable for large-scale power generation.
Strong grid compatibility: Most power systems in the world use alternating current, which has wide compatibility.

Disadvantages of AC:

Complexity: Since the frequency and phase of AC need to be precisely controlled, the design and maintenance of the power system are relatively complex.

Energy loss: AC will generate induced current during long-distance transmission, resulting in energy loss.

Advantages of DC:

High stability: The voltage and current of DC are constant, not affected by external electromagnetic interference, and suitable for use in electronic devices.

Convenient energy storage: DC can be directly stored in batteries, which is convenient for mobile and portable devices.

High energy transmission efficiency: DC has higher transmission efficiency under certain specific conditions, such as in high-voltage direct current (HVDC) systems.

Disadvantages of DC:

Difficult conversion: It is relatively difficult to increase and decrease the voltage of DC, and complex power electronic equipment is required.

Limited application: Since the global power grid is mainly based on AC, the applications of DC are relatively limited.
Q
What is AC?
A
AC stands for an alternating current, which refers to an electric current whose direction changes periodically over time, and the average current in one cycle is zero. Unlike direct current, its direction changes over time ,while direct current does not change periodically. The power generation is typically AC-most generators are based on an alternator which creates an alternating current as the wire stator turns within a magnetic field. AC power transmission is also preferred for high voltage transmission because it is relatively easy to step down the voltages for various applications with transformers.
Q
What is DC?
A
DC stands for direct current, which refers to an electric current that does not change in magnitude or direction over a certain period of time. DC is a constant current that flows in one direction only and does not alternate. For example, the current provides by dry cell batteries is DC. DC is used in a wide variety of applications, including testing equipment in research units and laboratories, battery charging, automotive applications, manufacturing testing, and solar panels. It is worth mentioning here that the power generated by photovoltaic panels is typical DC, which requires the use of a power inverter to convert it for standard power applications.
Q
What are the key differences between feeders and transmission lines?
A
 
 Feature  Feeder  Transmission Line
 Purpose  Distribute power locally            Transmit power over long distances
 Voltage Level            Low to medium  High to very high
 Length  Shorter  Longer
 Location  Urban and rural  Less populated areas
Q
What is a Transmission Line?
A
A transmission line is used to carry electricity over long distances. It connects power plants to substations and sometimes substations to substations. Key points about transmission lines include:

• Purpose: Transmit electricity over long distances.
• Voltage Level: High to very high voltage.
• Length: Much longer than feeders.
• Location: Often found in less populated areas.

Types of transmission lines
Transmission lines are also classified based on voltage levels and construction types. Here are the main types:
Type Description
Overhead Transmission Line Uses towers and conductors. Most common type.
Underground Transmission Line Buried under the ground. Used in urban areas.
High Voltage Direct Current (HVDC)                    Uses direct current. Efficient for very long distances.
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