This standard applies to the porcelain insulators for ac overhead power lines suitable for nominal system voltage greater than 1 000 volts and a frequency not greater than 100 Hz.
Note 1 — The specification applies to string insulator units, to insulator strings consisting of one-string insulator unit or an assembly of such units, and to rigid overhead line insulators. The specification applies to insulators of the same type when used in sub-stations. It does not apply to insulators forming part of electrical apparatus or to parts used in their construction.
Note 2 — This specification applies to insulators for use on ac overhead lines and may be regarded as a provisional specification for insulators for use on dc overhead lines.
IS 731-1971 history
1972IS 731-1971 Specification for porcelain insulators for overhead power lines with nominal voltages greater than 1000 V