Question

The insulators used in transmission lines at river and road crossing are:

• A. Strain type
• B. Suspension type
• C. Pin type
• D. Cup type

Hint:

When a transmission line changes direction, terminates at a dead-end, or spans an obstacle like a river or highway, always specify Strain Insulators to handle the increased mechanical tension.

Answer 1

The Correct Option is A

Concept: Overhead transmission line insulators must provide adequate electrical insulation while withstanding heavy mechanical loads. Different structural configurations are used depending on the path of the line: * Pin Insulators: Used horizontally on straight line runs for lower voltages (up to $33\text{ kV}$). * Suspension Insulators: Used vertically on high-voltage lines, where the conductor string hangs freely below the cross-arm. * Strain/Tension Insulators: Installed horizontally in line with the conductors at dead-ends, sharp curves, or long spans (such as river, valley, or major road crossings) to sustain high mechanical tension.

Step 1: Analyze the mechanical requirements at river and road crossings.
River and road crossings require longer spans between support towers to clear the geographic obstacle safely. These long spans experience significantly higher mechanical tension due to the weight of the conductor and potential wind or ice loading.

Step 2: Evaluate insulator performance under high tension.
* Suspension insulators hang vertically and are designed primarily to support vertical loads rather than high axial tensile stress. * Strain insulators are anchored horizontally to the tower cross-arms in line with the span. This assembly transfers the high directional tensile loads safely from the long span to the structural steel tower frame. Therefore, strain-type insulators are used at river and road crossings to handle the high mechanical tension. This corresponds to Option (A).