What is classification of overhead transmission?
2 Answers
Overhead transmission refers to the system used to transport electrical power from generating stations to distribution systems through transmission lines suspended on towers. These lines are located above the ground, and the classification of overhead transmission systems can be based on several criteria, such as voltage level, conductor configuration, types of insulators, and distance.
Here's a detailed explanation of the various classifications:
### 1. **Classification Based on Voltage Levels**
The most common way to classify overhead transmission systems is by the voltage level they operate at. The voltage level dictates how much power can be transmitted, the size of the conductor, and the structure required to support the transmission lines.
- **Low Voltage (LV):**
- Voltage level: Less than 1 kV
- Used for local distribution, such as in residential areas.
- **Medium Voltage (MV):**
- Voltage level: Between 1 kV and 33 kV
- Typically used for distributing electricity within cities and smaller areas.
- **High Voltage (HV):**
- Voltage level: Between 33 kV and 220 kV
- Used for transmitting electricity over moderate distances. Commonly seen in regional power transmission networks.
- **Extra High Voltage (EHV):**
- Voltage level: Between 220 kV and 800 kV
- Used for long-distance, high-capacity power transmission. Requires specialized insulation and larger towers to prevent energy losses and maintain safety.
- **Ultra High Voltage (UHV):**
- Voltage level: Above 800 kV
- Used in rare cases for very long distances and high power transmission, such as in large national grids.
### 2. **Classification Based on Conductor Configuration**
The conductor is the metallic wire that carries the electricity. Different configurations of conductors can be used, depending on the power demand and the distance over which power needs to be transmitted.
- **Single Circuit:**
- Consists of three-phase conductors (and sometimes a ground wire).
- Typically used for local and regional distribution.
- **Double Circuit:**
- Two sets of three-phase conductors on the same tower.
- Increases the transmission capacity without requiring a second tower, and improves reliability by providing redundancy.
- **Multi-Circuit:**
- More than two circuits are used on the same tower. This configuration is less common but can be used when there is a need to transmit large amounts of power in confined spaces.
- **Bundle Conductor:**
- Used in high voltage and extra-high voltage transmission.
- A bundle of two or more conductors is used per phase to reduce energy losses, minimize the corona effect, and increase the current-carrying capacity.
### 3. **Classification Based on Types of Insulators**
Insulators are crucial components in overhead transmission lines, used to prevent the electric current from flowing to the tower or ground. Overhead transmission systems are also classified based on the type of insulators used:
- **Pin Insulator:**
- Commonly used for voltages up to 33 kV.
- The conductor is mounted on the top of the insulator.
- **Suspension Insulator:**
- Used for higher voltage transmission lines, typically above 33 kV.
- These insulators are suspended from the cross-arm of the transmission tower, and multiple insulators can be connected in series for extra insulation.
- **Strain Insulator:**
- Used at dead-end poles and where there is a sharp change in the direction of transmission lines.
- Designed to withstand the tension or mechanical stress exerted by the conductors.
- **Shackle Insulator:**
- Used in low-voltage transmission lines (up to 11 kV) and distribution systems.
- Compact and often seen in urban areas for small spans.
### 4. **Classification Based on Transmission Distance**
Another classification is based on the distance the electricity must travel from the generating station to the end user.
- **Short-Distance Transmission:**
- Distance: Less than 50 km
- These lines typically operate at low or medium voltage.
- Common in local or urban distribution systems.
- **Medium-Distance Transmission:**
- Distance: Between 50 km and 200 km
- Operates at high voltage (33 kV – 132 kV).
- These lines are often used for regional power distribution.
- **Long-Distance Transmission:**
- Distance: Greater than 200 km
- Typically uses extra-high voltage (above 220 kV) or ultra-high voltage lines.
- Used to transmit power over vast regions, sometimes across states or even national borders.
### 5. **Classification Based on Support Structure**
Transmission lines are supported by various types of towers or poles, depending on factors such as voltage level, terrain, and the span between the towers.
- **Wooden Poles:**
- Commonly used for low-voltage distribution lines.
- These poles are inexpensive and easy to install but are not suitable for high voltages.
- **Steel Towers (Lattice Towers):**
- Used for high-voltage and extra-high-voltage transmission.
- They provide strong structural support and are designed to carry heavy conductor loads over long spans.
- **Concrete Poles:**
- Often used for medium voltage systems, especially in urban areas.
- More durable than wood but less flexible than steel towers.
- **Monopole Towers:**
- Used in areas where space is a concern or in urban environments.
- Typically used for lower voltage lines but can also be seen supporting high voltage lines when aesthetics or space are important considerations.
### 6. **Classification Based on Location or Terrain**
- **Urban Transmission:**
- In cities, overhead lines face challenges like space constraints and aesthetic concerns. Poles or compact steel towers are used.
- **Rural Transmission:**
- In rural areas, long spans between towers are possible, and larger steel lattice towers are more commonly used.
- **Mountainous or Hilly Terrain:**
- In challenging terrains, special towers and high-tension support are required to accommodate the varying heights and distances between the towers.
### Conclusion
The classification of overhead transmission lines is a complex but organized system that helps optimize the efficiency, safety, and reliability of power transmission. Whether based on voltage, conductor type, insulator design, or distance, each classification plays a crucial role in how energy is distributed from generation plants to homes and businesses.
Understanding these classifications is essential for engineers, utility companies, and policymakers who design and manage electrical grids.
Here's a detailed explanation of the various classifications:
### 1. **Classification Based on Voltage Levels**
The most common way to classify overhead transmission systems is by the voltage level they operate at. The voltage level dictates how much power can be transmitted, the size of the conductor, and the structure required to support the transmission lines.
- **Low Voltage (LV):**
- Voltage level: Less than 1 kV
- Used for local distribution, such as in residential areas.
- **Medium Voltage (MV):**
- Voltage level: Between 1 kV and 33 kV
- Typically used for distributing electricity within cities and smaller areas.
- **High Voltage (HV):**
- Voltage level: Between 33 kV and 220 kV
- Used for transmitting electricity over moderate distances. Commonly seen in regional power transmission networks.
- **Extra High Voltage (EHV):**
- Voltage level: Between 220 kV and 800 kV
- Used for long-distance, high-capacity power transmission. Requires specialized insulation and larger towers to prevent energy losses and maintain safety.
- **Ultra High Voltage (UHV):**
- Voltage level: Above 800 kV
- Used in rare cases for very long distances and high power transmission, such as in large national grids.
### 2. **Classification Based on Conductor Configuration**
The conductor is the metallic wire that carries the electricity. Different configurations of conductors can be used, depending on the power demand and the distance over which power needs to be transmitted.
- **Single Circuit:**
- Consists of three-phase conductors (and sometimes a ground wire).
- Typically used for local and regional distribution.
- **Double Circuit:**
- Two sets of three-phase conductors on the same tower.
- Increases the transmission capacity without requiring a second tower, and improves reliability by providing redundancy.
- **Multi-Circuit:**
- More than two circuits are used on the same tower. This configuration is less common but can be used when there is a need to transmit large amounts of power in confined spaces.
- **Bundle Conductor:**
- Used in high voltage and extra-high voltage transmission.
- A bundle of two or more conductors is used per phase to reduce energy losses, minimize the corona effect, and increase the current-carrying capacity.
### 3. **Classification Based on Types of Insulators**
Insulators are crucial components in overhead transmission lines, used to prevent the electric current from flowing to the tower or ground. Overhead transmission systems are also classified based on the type of insulators used:
- **Pin Insulator:**
- Commonly used for voltages up to 33 kV.
- The conductor is mounted on the top of the insulator.
- **Suspension Insulator:**
- Used for higher voltage transmission lines, typically above 33 kV.
- These insulators are suspended from the cross-arm of the transmission tower, and multiple insulators can be connected in series for extra insulation.
- **Strain Insulator:**
- Used at dead-end poles and where there is a sharp change in the direction of transmission lines.
- Designed to withstand the tension or mechanical stress exerted by the conductors.
- **Shackle Insulator:**
- Used in low-voltage transmission lines (up to 11 kV) and distribution systems.
- Compact and often seen in urban areas for small spans.
### 4. **Classification Based on Transmission Distance**
Another classification is based on the distance the electricity must travel from the generating station to the end user.
- **Short-Distance Transmission:**
- Distance: Less than 50 km
- These lines typically operate at low or medium voltage.
- Common in local or urban distribution systems.
- **Medium-Distance Transmission:**
- Distance: Between 50 km and 200 km
- Operates at high voltage (33 kV – 132 kV).
- These lines are often used for regional power distribution.
- **Long-Distance Transmission:**
- Distance: Greater than 200 km
- Typically uses extra-high voltage (above 220 kV) or ultra-high voltage lines.
- Used to transmit power over vast regions, sometimes across states or even national borders.
### 5. **Classification Based on Support Structure**
Transmission lines are supported by various types of towers or poles, depending on factors such as voltage level, terrain, and the span between the towers.
- **Wooden Poles:**
- Commonly used for low-voltage distribution lines.
- These poles are inexpensive and easy to install but are not suitable for high voltages.
- **Steel Towers (Lattice Towers):**
- Used for high-voltage and extra-high-voltage transmission.
- They provide strong structural support and are designed to carry heavy conductor loads over long spans.
- **Concrete Poles:**
- Often used for medium voltage systems, especially in urban areas.
- More durable than wood but less flexible than steel towers.
- **Monopole Towers:**
- Used in areas where space is a concern or in urban environments.
- Typically used for lower voltage lines but can also be seen supporting high voltage lines when aesthetics or space are important considerations.
### 6. **Classification Based on Location or Terrain**
- **Urban Transmission:**
- In cities, overhead lines face challenges like space constraints and aesthetic concerns. Poles or compact steel towers are used.
- **Rural Transmission:**
- In rural areas, long spans between towers are possible, and larger steel lattice towers are more commonly used.
- **Mountainous or Hilly Terrain:**
- In challenging terrains, special towers and high-tension support are required to accommodate the varying heights and distances between the towers.
### Conclusion
The classification of overhead transmission lines is a complex but organized system that helps optimize the efficiency, safety, and reliability of power transmission. Whether based on voltage, conductor type, insulator design, or distance, each classification plays a crucial role in how energy is distributed from generation plants to homes and businesses.
Understanding these classifications is essential for engineers, utility companies, and policymakers who design and manage electrical grids.