What is a Suspension Type Insulator?
The main function of a suspension insulator is to separate the line conductors and support them electrically. It comprises several porcelain insulator units connected by metal links to form a flexible string. The conductor is usually connected to the bottom of the string.
Suspension Insulator Diagram
The suspension type insulator diagram below illustrates how the porcelain units are arranged in a string.
Advantages of Suspension Type Insulator
These high-voltage overhead line insulators offer the following advantages,
- Depending on the voltage, the appropriate number of discs are connected in series with the string, with each unit operating at about 11kV.These insulators are typically used for voltages above 33 kV and can be employed up to 765 kV or more in extra high voltage (EHV) transmission lines.
- If one unit is damaged, it can be replaced instead of the entire string.
- The transmission line provides great flexibility as the string can swing freely in any direction.
- The suspension insulators are placed above the conductors, and thus, they provide partial lightning protection.
Disadvantages of Suspension Type Insulator
- Higher Initial Cost: Suspension insulators cost more than pin or post types because they use multiple units and fittings.
- Frequent Maintenance: Pollution and weather can affect each unit in the string, so they require regular cleaning and inspection.
- Heavier Setup: Their weight demands stronger and more expensive supporting structures.
- Time-Consuming Installation: Assembling and aligning several discs takes more time during installation.
- Requires More Clearance: Higher voltage needs longer strings, which increases the required vertical clearance.
Types of Suspension Insulators
There are two main types of suspension insulators
- Cap and Pin Type
- Hewlett or Interlink Type
Below is a detailed explanation of the cap-and-pin, and Hewlett-type insulator.
1. Cap-and-pin type Suspension Insulator
A porcelain cap-and-pin unit is connected by either a ball and socket or clevis-pin to a galvanized cast iron or forged steel cap and a galvanized forged steel pin.
2. Interlink Type Insulator
The unit uses porcelain with two curved channels intersecting at right angles. U-shaped covered steel links pass through these channels to connect the unit. This type of insulator is known as the Hewlett insulator.
The interlink-type insulators are mechanically stronger than the cap-and-pin type units. The metallic link continues to support the line even if the porcelain between the links breaks; thus, the supply is not interrupted.
The Hewlett-type insulator has one major disadvantage: the porcelain between the links is highly electrically stressed, causing its puncture stress to be less than that of other types.
Applications of Suspension Insulator
Suspension insulators are widely used in high-voltage transmission and distribution systems due to their modular construction and mechanical strength. Typical applications include:
- Overhead power lines operating at voltages above 33 kV, often going up to 765 kV or more in extra high voltage (EHV) and ultra-high voltage (UHV) systems.
- Long-span line crossings, such as over rivers or valleys, where mechanical flexibility is essential.
- Substations and switchyards, where space constraints and high voltages require reliable support and insulation.
- Railway electrification systems for power distribution to locomotives.
- Polluted or coastal environments, where longer insulator strings reduce leakage current and flashover risk.
Conclusion
In conclusion, suspension insulators play a vital role in overhead power transmission. They offer robust support and reliable insulation for conductors. The Cap and Pin and Composite Suspension Insulators have advantages like high mechanical strength and resistance to environmental factors.
Reference: https://www.electricalvolt.com/insulators-used-in-overhead-power-lines/
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