Introduction:
Insulators are used in electrical power systems to support and isolate conductors from the ground or other conductive objects. They prevent the flow of electrical current and ensure the safe and reliable transmission of power. The type of insulator used depends on various factors such as voltage level, mechanical load requirements, and environmental conditions.

Types of Insulators:
There are several types of insulators available for different applications. However, for dead ends and straight lines as suspension types for voltages 3.3 kV and above, the most suitable type of insulator is the strain insulator.

Reasons for using strain insulators:
1. Mechanical strength: Strain insulators are designed to withstand high mechanical loads. They are used at dead ends and on straight lines to provide support and maintain the required tension in the conductors.

2. Voltage insulation: Strain insulators have high voltage insulation capabilities. They can effectively withstand the electrical stress imposed on them by the high voltages used in power transmission systems.

3. Flexibility: Strain insulators are flexible in nature, allowing them to absorb and dampen the mechanical vibrations and stresses caused by wind, ice, and other environmental factors. This flexibility helps in reducing the chances of conductor damage and ensures the longevity of the insulator.

4. Easy installation: Strain insulators can be easily installed and replaced, which makes them suitable for dead ends and straight lines. They can be attached to the supporting structures using suitable hardware and can be adjusted to achieve the desired tension in the conductors.

5. Cost-effective: Strain insulators are relatively cost-effective compared to other types of insulators. They provide the necessary mechanical strength and voltage insulation required for dead ends and straight lines at a reasonable cost.

Conclusion:
Strain insulators are the most suitable type of insulators used at dead ends and on straight lines as suspension types for voltages 3.3 kV and above. They offer high mechanical strength, voltage insulation capabilities, flexibility, easy installation, and cost-effectiveness, making them an ideal choice for these applications.