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T/F: corona inception voltage and GMR

Short answer

FALSE. Corona inception voltage depends on the conductor's physical outer radius r, not its GMR. It is roughly proportional to r (V_d ∝ r ln(D/r)), increasing as radius increases, so it is not inversely proportional.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: Corona inception voltage is inversely proportional to the GMR of conductor.

FALSE.

The corona inception (disruptive critical) voltage is

Vd=21.1 m0 δ rln⁡Dr kVV_d = 21.1\,m_0\,\delta\,r\ln\frac{D}{r}\ \text{kV}
  • VdV_d depends on the physical outer radius rr, which sets the surface field. It does not depend on the GMR.
  • GMR (about 0.7788r0.7788r for a solid conductor) is a fictitious radius used only for inductance calculations.
  • VdV_d increases with radius: it is nearly proportional to rr, because rln⁡(D/r)r\ln(D/r) rises with rr for D≫rD \gg r. It is not inversely proportional.

So a larger conductor, or a bundle with a larger equivalent radius, raises the corona inception voltage. The statement is wrong on both counts.

✓ Answer checked by Claude Opus 5.5 (high effort)

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