Skip to main content

T/F: pin insulator cost vs voltage

Short answer

FALSE. Pin insulator cost increases faster than linearly with voltage, roughly with the square or cube of voltage, because the porcelain volume grows nonlinearly and large pieces are difficult to fabricate. Above 33 kV suspension strings offer nearly linear cost scaling.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: On increasing the voltage level, the cost of pin type insulator varies linearly.

FALSE.

The cost of a pin insulator does not rise linearly with voltage. It rises much faster than linearly, roughly with a power of the voltage between 2 and 3.

  • A higher voltage needs more creepage and flashover distance. So the insulator needs more porcelain sheds and a greater height and diameter. Its volume, and therefore its weight and cost, grows roughly with the cube of its linear size.
  • Large porcelain pieces are hard to fire uniformly. Above about 25–33 kV the insulator must be made in two or three parts cemented together, which adds cost.
  • A taller insulator also needs a stronger and longer pin to resist the bending moment.

For this reason pin insulators become uneconomical above about 33 kV. Suspension (string) insulators are used instead, because their cost rises nearly linearly with voltage: one disc is added per about 11 kV.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Transmission and Distribution System Design chapter 3 questions →