Why might a string of disc insulators be preferred over a single long insulator?

• A. It is heavier than a single long insulator
• B. It cannot be used in high voltage
• C. It has lower breakdown strength
• D. It provides higher breakdown strength, allows for longer creepage paths, and better mechanical flexibility

Answer: (D)

The main idea is that stacking disc insulators creates a higher voltage rating by distributing the electric stress across several discs, while also increasing the distance a surface discharge would have to travel and improving mechanical handling.

Each disc in the string shares part of the voltage, so the total breakdown strength of the assembly is higher than a single disc of the same material. The long path along the surfaces and gaps between the discs—the creepage path—is naturally longer, which helps resist surface leakage and flashover in polluted or damp environments. The modular stack also offers better mechanical flexibility; joints between discs can accommodate movement and reduce concentrated stresses in a single rigid element.

So, a string of discs is preferred because it provides higher breakdown strength, longer creepage paths, and improved mechanical flexibility, which are all advantageous for high-voltage installations.