What is the primary function of an insulator in a power system?

• A. To prevent voltage from appearing on the conductor.
• B. To store energy for surge events.
• C. To increase system voltage.
• D. To prevent current from flowing from the conductor to the supporting structure and to withstand electrical and environmental stresses.

Answer: (D)

The main idea is that an insulator keeps the live conductor from energizing the supporting structure while standing up to the electrical and environmental stresses it faces. It provides dielectric isolation so only a tiny, controlled leakage might occur and so arcing to the tower is prevented. At the same time it must be mechanically strong to hold the conductor in place against wind, ice, and vibration, and it has to withstand conditions like rain, pollution, and temperature changes that can affect insulation performance. That’s why it’s designed to resist both electrical stress (high voltage) and environmental stress, ensuring safe clearance and reliable operation.

The other options don’t fit because: insulators don’t store energy for surge events (that’s a job for surge protection devices), they don’t raise system voltage, and they don’t prevent voltage from appearing on the conductor—their purpose is to stop current from flowing to the supporting structure while insulating the live parts.