What number of string of insulators is used for 132 kV transmission if a suspension type insulator is used for overhead lines? 

Explanation:

For a 132 kV transmission line using a suspension type insulator for overhead lines, the number of string insulators required is a critical factor for ensuring the reliability and safety of the electrical transmission. The correct option for the number of string insulators used in this scenario is option 1, which states that 12 insulators are required. Let’s delve into the details to understand why this is the correct option and analyze the other options as well.

Importance of Insulators in Transmission Lines:

Insulators play a vital role in overhead transmission lines. They provide the necessary insulation between the live conductors and the transmission towers or poles, preventing electrical discharges to the ground. They also support the weight of the conductors and withstand various mechanical stresses. The number of insulators in a string depends on several factors, including the transmission voltage, environmental conditions, and the type of insulators used.

Factors Determining the Number of Insulators:

• Voltage Level: Higher transmission voltages require more insulators in the string to provide adequate insulation. For a 132 kV transmission line, a specific number of insulators are needed to withstand the voltage without breaking down.
• Environmental Conditions: The number of insulators may vary based on the environmental conditions such as pollution, humidity, and altitude. In areas with heavy pollution or coastal regions, additional insulators may be required to prevent flashovers.
• Type of Insulator: Different types of insulators, such as porcelain or glass, might have different dielectric strengths and mechanical properties. The choice of insulator material can influence the number of insulators needed in a string.

Calculation for 132 kV Transmission Line:

For a 132 kV transmission line, the standard number of insulators used in a suspension string is typically 12. This is based on the following considerations:

• Dielectric Strength: Each insulator unit can withstand a specific voltage, typically around 11 kV to 15 kV. For 132 kV, dividing this voltage by the average withstand voltage per insulator unit gives us approximately 9 to 12 insulators. To ensure a margin of safety and account for any environmental factors, 12 insulators are used.
• Mechanical Strength: The insulators also need to support the mechanical load of the conductors, including wind and ice loads. A string of 12 insulators provides sufficient mechanical strength for these loads.
• Safety Margin: Electrical and mechanical safety margins are critical in transmission line design. Using 12 insulators ensures that the system can withstand higher than expected voltages and mechanical stresses.

Correct Option Analysis:

The correct option for the number of string insulators used for 132 kV transmission is:

Option 1: 12

This option is correct because it aligns with the standard design practice for 132 kV transmission lines, considering both electrical and mechanical requirements. Using 12 insulators ensures adequate insulation and mechanical support, providing a reliable and safe transmission line.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: 4

This option is incorrect because using only 4 insulators for a 132 kV transmission line would not provide sufficient insulation. The dielectric strength of 4 insulators would be inadequate to withstand the 132 kV voltage, leading to a high risk of electrical breakdown and flashover.

Option 3: 2

This option is also incorrect. Using only 2 insulators for a 132 kV transmission line is far below the required number. Such a small number of insulators would not provide the necessary dielectric strength or mechanical support, making the transmission line highly unsafe and unreliable.

Option 4: 6

This option is incorrect as well. Although 6 insulators might provide some level of insulation, it would still be insufficient for a 132 kV transmission line. The safety margin would be too low, and the risk of electrical breakdown and mechanical failure would be high.

Conclusion:

Understanding the requirements for insulators in transmission lines is essential for ensuring the safety and reliability of electrical power systems. For a 132 kV transmission line using suspension type insulators, the standard number of insulators in a string is 12. This number provides the necessary dielectric strength, mechanical support, and safety margins to operate the transmission line reliably under various conditions. Analyzing the other options highlights the importance of adhering to standard practices and design considerations in transmission line construction.