The characteristic impedance of a transmission line is a critical parameter for maintaining voltage stability and maximizing power transfer efficiency. When a power line is terminated with a load impedance that is equal to its characteristic impedance, it is called impedance matching.

When the line is impedance-matched, it behaves as if it were infinitely long, and there are no voltage or current reflections at the load end. This prevents standing waves, minimizes power losses, and helps maintain a stable voltage profile along the line. For our OHTL and underground cable laying equipment, understanding this principle is crucial for designing and implementing stable and efficient power systems.

Surge Impedance Loading (SIL) is the power level at which a transmission line is terminated with a load equal to its surge impedance. At this specific loading point, the reactive power generated by the line's capacitance is perfectly balanced by the reactive power consumed by its inductance. This balance results in a flat, stable voltage profile along the entire length of the line, and the line operates with maximum efficiency and minimal losses.

SIL is a benchmark used by engineers to evaluate the performance of a transmission line. For long transmission lines, operating significantly above SIL can cause a voltage drop, while operating below SIL can lead to overvoltage. Our company's tools and equipment are designed to help our customers build and maintain power systems that can be operated close to their surge impedance loading for optimal performance.

A corona ring works on the principle of electric field distribution. The electric field is most intense at points of high curvature, such as sharp edges or corners on hardware and conductors. By installing a smooth, rounded, conductive ring around these points, the ring effectively increases the curvature and spreads the electric charge over a larger area. This significantly reduces the localized electric field intensity to a level below the point at which air begins to ionize.

The benefits of using corona rings are substantial:

• Minimizes Power Loss: Corona discharge is a form of energy dissipation. By preventing it, the system's efficiency is improved, especially on long-distance transmission lines.

• Reduces Equipment Damage: The ozone and nitric acid produced by corona discharge are corrosive and can cause materials like insulators to age and fail prematurely. The rings protect these components, extending their service life.

• Mitigates Radio and Audible Noise: The electrical disturbances from corona discharge can cause interference with radio communications and produce audible hissing or cracking sounds. Corona rings eliminate this unwanted noise.

• Enhances System Reliability: By preventing flashovers and equipment failure due to corona, the rings contribute to the overall stability and reliability of the power grid.

While they are often used together and share a similar appearance, a corona ring and a grading ring have distinct primary functions.

• A corona ring's main purpose is to prevent corona discharge by lowering the electric field gradient around a high-voltage point. It is typically used for system voltages above 230 kV.

• A grading ring, on the other hand, is primarily used to equalize the electric field and voltage distribution along a string of insulators. This is important because without the ring, the electric field is strongest at the conductor end of the insulator string. The grading ring helps to distribute the stress more uniformly across all the insulators, preventing premature electrical breakdown and improving the overall efficiency and lifespan of the insulator string.

In many modern applications, a single ring can be designed and placed to perform both functions, but their fundamental roles are different.

Answer: Transmission lines can be classified in several ways to better understand their behavior, design, and application. The most common classifications are:

• By Length: This is the most prevalent method, dividing lines into short, medium, and long categories. This classification is crucial for determining how to model the line's electrical characteristics (resistance, inductance, and capacitance).

• By Voltage Level: Lines are categorized as High Voltage (HV), Extra High Voltage (EHV), or Ultra High Voltage (UHV) based on their operating voltage, which dictates their power-carrying capacity and the distance they can efficiently transmit electricity.

• By Configuration: This classifies lines based on their physical placement, such as overhead transmission lines, underground cables, or submarine cables.

Answer: The primary difference lies in their length and the way their electrical parameters (resistance, inductance, and capacitance) are considered in analysis.

• Short Transmission Lines: Typically less than 80 km in length with voltages below 20 kV. For these lines, the effects of capacitance are considered negligible, and the line is modeled as a simple series circuit with only resistance and inductance.

• Medium Transmission Lines: Have a length between 80 km and 250 km, with voltages between 20 kV and 100 kV. The capacitance effects are significant and are accounted for by lumping the capacitance at one or more points along the line (e.g., Nominal-T or Nominal-Pi methods).

• Long Transmission Lines: Are over 250 km long and operate at voltages above 100 kV. For these lines, all three parameters (resistance, inductance, and capacitance) are distributed uniformly along the entire length, requiring more complex analysis using distributed parameter models.

Answer: Classifying transmission lines is essential for accurate system analysis, design, and performance prediction. By categorizing lines based on their length, voltage, or configuration, engineers can use the appropriate mathematical models to calculate and ensure factors like:

• Voltage Regulation: Maintaining a stable voltage at the receiving end of the line.

• Power Transfer Capability: Maximizing the amount of power that can be safely transmitted.

• Line Efficiency: Minimizing power losses during transmission.

• Equipment Selection: Choosing the correct tools and equipment, such as the tension stringing and cable laying equipment we specialize in, for building and maintaining the line.

This is a crucial topic for line maintenance. Faults are typically classified into two main categories:

• Symmetrical Faults: These are three-phase faults where all phases are short-circuited together. These are the most severe but least common type of fault.

• Asymmetrical Faults: These are more common and include:

  • Single Line-to-Ground (LG) Fault: The most frequent type, where one conductor makes contact with the ground.

  • Line-to-Line (LL) Fault: A short circuit between two conductors.

  • Double Line-to-Ground (LLG) Fault: A short circuit between two conductors and the ground.

Understanding these classifications is vital for our customers who use our products for the maintenance and repair of these power lines.

This is a critical consideration in any project involving both power and data. The key is to physically separate the two types of lines. We advise following these best practices to minimize electromagnetic interference (EMI) and radio frequency interference (RFI):

1. Maintain Separation: Whenever possible, keep a minimum distance of at least 6 inches (15 cm) between power cables and coaxial cables.

2. Separate Conduits: Never run power cables and coaxial cables in the same conduit or cable tray.

3. Cross at Right Angles: If the lines must cross, ensure they do so at a 90-degree angle to minimize the area of interaction between their electromagnetic fields.

4. Use Quality Shielding: Ensure the coaxial cables are of high quality with effective shielding (braided or foil) to provide better protection against external fields.

Our commitment to safety and quality extends to providing the right equipment for the right application, helping our clients implement these best practices on-site.

Answer: The choice between overhead and underground power transmission lines depends on a project's specific requirements, including budget, environmental impact, and location. Overhead lines, supported by towers or poles, are generally more cost-effective and easier to install and maintain. They are ideal for rural or long-distance transmission projects. In contrast, underground cables offer greater aesthetic appeal and are less susceptible to weather-related damage, making them the preferred choice for urban and environmentally sensitive areas.

At Ningbo Changshi, we provide a complete one-stop supply of specialized equipment for both. Our range includes overhead transmission line (OHTL) wire cable conductor tension stringing equipment and a full line of underground cable laying equipment, allowing us to support your project no matter the chosen method.

Answer: The latest and most significant trend in power line conductors is the increasing adoption of High-Temperature Low-Sag (HTLS) conductors. These innovative conductors can operate at higher temperatures without sagging, which allows them to carry more current (and thus, more power) on existing transmission towers. This technology is crucial for modern grids, as it helps increase capacity and efficiency without the need for extensive new infrastructure.

Our company is at the forefront of this shift, providing state-of-the-art tension stringing equipment and wire cable conductor pulling equipment specifically designed to handle the unique properties of these advanced HTLS and other high-capacity conductors.

Answer: The success of a modern overhead transmission line (OHTL) project relies on a comprehensive suite of high-quality tools and equipment. Beyond the conductors and towers themselves, essential equipment includes:

• Hydraulic tensioners and pullers: Used for precision control during the conductor stringing process.

• Conductor stringing blocks: Ensure the cables are protected and smoothly guided along the line.

• Anti-twisting braided steel wire rope: Prevents cable twisting and damage during pulling.

• Compression tools and dies: For secure, high-quality conductor connections.

• Come-along clamps and grips: Essential for safe handling and tensioning.

At Ningbo Changshi, we specialize in manufacturing and exporting all these items and more, providing a single source for all your OHTL construction and maintenance needs. We are dedicated to providing the most reliable and efficient tools to ensure the quality and safety of your projects.

Answer: The Corona Effect is a phenomenon where the air surrounding a high-voltage conductor becomes ionized, leading to a partial electrical discharge. This can be observed as a faint, bluish-purple glow, accompanied by a hissing sound and the production of ozone gas. The Corona Effect is undesirable as it causes power loss, radio interference, and can accelerate the aging of equipment. It becomes a design concern for power lines at 230 kV and higher. The effect can be mitigated by using larger conductor diameters, bundle conductors, and specific hardware to reduce the electric field gradient at the conductor's surface.

Answer: The primary types of power loss in transmission lines are:

• Resistive (I²R) Losses: This is the most significant type of loss, caused by the inherent resistance of the conductors, which dissipates energy as heat.

• Corona Losses: Energy dissipated as a result of the Corona Effect.

• Inductive and Capacitive Losses: These are caused by the magnetic and electric fields generated by alternating current, leading to energy dissipation.

These losses can be minimized by:

• Increasing Transmission Voltage: This is the most effective method, as it directly reduces resistive losses.

• Optimizing Conductor Design: Using conductors with a larger cross-sectional area or bundle conductors to reduce resistance and the Corona Effect.

• Selecting High-Quality Materials: Employing materials with low resistance and advanced insulation.

As a leading manufacturer of power line equipment, we at Ningbo Changshi are experts in providing the tools and hardware necessary to build and maintain high-efficiency transmission lines that minimize these losses.

Why are power transmission lines transposed?