**a) The Concept of Wires and Cables and the Difference Between Them:**
Wires and cables are essential components used for transmitting power, data, and signals in various applications. While the terms "wire" and "cable" are often used interchangeably, they do have distinct differences based on structure, size, and purpose. Generally, a wire refers to a single conductor with a small number of cores, a compact diameter, and a simple structure. If it has no insulation, it is called a bare wire. Any conductor that is insulated or has a more complex structure is typically referred to as a cable.
A conductor with a cross-sectional area larger than 6 mm² is considered a large wire, while one smaller than or equal to 6 mm² is called a small wire. Insulated wires are also known as "cloth wires." Wires and cables come in many forms, including bare wires, insulated wires, power cables, communication cables, and optical fibers.
The naming of wires and cables can be quite detailed, but in practice, people often use simplified names along with model specifications to refer to them. For example, "low voltage cable" might represent all plastic-insulated power cables rated at 0.6/1 kV. Although the full name of a product may not always be clear, its model specification usually provides enough detail to identify the exact product.
**Principles for Naming Wire and Cable Products:**
1. **Content in the Product Name:**
- The application or category of the product
- The material or type of construction
- Key features or additional characteristics (usually in this order)
2. **Structure Description Order:**
When describing the structure, it should follow an inside-out principle: conductor → insulation → inner sheath → outer sheath → armor.
3. **Simplification:**
In cases where there is no confusion, some parts of the description may be abbreviated. For example, aluminum conductors are not commonly used in automotive wiring, so their material may be omitted.
**Examples of Cable Naming:**
Take the example of a "rated voltage 8.7/15kV flame-retardant copper core XLPE insulated steel tape armored PVC sheathed power cable." Here’s what each part means:
- "Rated voltage 8.7/15kV" – indicates the application and voltage rating
- "Flame-retardant" – highlights a special feature
- "Copper core" – specifies the conductor material
- "XLPE insulated" – identifies the insulation material
- "Steel tape armored" – describes the armor type and material
- "PVC sheathed" – refers to the outer sheath material
- "Power cable" – the overall product category
In terms of model notation, the format is generally: [1: category/use] [2: conductor] [3: insulation] [4: inner sheath] [5: structural features] [6: outer sheath or derivative] [-7: usage characteristics]. Items 1–5 and 7 are represented by pinyin letters, while polymer materials are shown using English letters. Numbers are used for the sixth part. Copper is the most common conductor, so it is often omitted unless specified otherwise.
**What is a Cable Intermediate Connector?**
An intermediate connector is a device used to connect two sections of a cable, ensuring continuity of the conductor, insulation shield, and protective layer. It plays a crucial role in maintaining the integrity of the cable line.
**What is the Main Electrical Wiring?**
Main electrical wiring refers to the arrangement of major electrical equipment and busbars in power plants and substations. It includes the main busbars and plant power systems, designed according to specific functional requirements.
**Rules for Selecting the Cross-Section of a Power Cable:**
When selecting the right cable size, consider the following:
1. The cable's rated voltage must be equal to or higher than the system voltage at the installation point.
2. The continuous allowable current of the cable should match or exceed the maximum load current.
3. The cross-section must meet short-circuit stability requirements.
4. Check that the voltage drop is within acceptable limits based on the cable length.
5. Ensure the minimum short-circuit current at the end of the line allows for reliable protection.
**Advantages of Cross-Linked Polyethylene (XLPE) Cables Over Oil-Paper Cables:**
1. Easier to install due to a smaller bending radius and lighter weight.
2. Not limited by line drop constraints.
3. Excellent thermal performance, allowing higher operating temperatures and greater power capacity.
4. Simple and dry-type accessories.
5. Low maintenance and no oil leakage issues.
6. More cost-effective.
7. Higher reliability and fewer failures.
8. Fewer manufacturing steps, simpler processes, and better economic returns.
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