--- title: "T/F: pin insulator cost vs voltage" subject: "Transmission and Distribution System Design" chapter: 3 key: "semester_8/transmission_and_distribution_system_design:tf-pin-insulator-cost-linear" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-pin-insulator-cost-linear site: BCT Engineering --- # T/F: pin insulator cost vs voltage Transmission and Distribution System Design · Chapter 3: Overhead Line Insulator Design - Asked in: 2071 Magh, 1+3 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-pin-insulator-cost-linear - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-3 ## Question 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. ## 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. ## Answer **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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Does the cost of a pin insulator vary linearly with voltage? A. True: one disc per 11 kV B. False: it falls with voltage C. False: it rises much faster than linearly D. True: it doubles when voltage doubles Answer: C. Cost grows roughly with a power of 2 to 3 of the voltage. (Key point: Verdict) 2. Why does cost rise so fast? A. Size and volume grow roughly as the cube of linear size, and large porcelain pieces are hard to fire B. Pins are not needed C. Voltage does not affect size D. Porcelain becomes cheaper Answer: A. More sheds, height and diameter increase volume and manufacturing difficulty. (Key point: Reason) 3. What replaces pin insulators above about 33 kV? A. Shackle insulators B. Larger pin insulators C. No insulators D. Suspension string insulators, whose cost rises nearly linearly Answer: D. One disc is added per about 11 kV. 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