Protection Engineering Basics and Schemes Protection Engineering | Page 235
V P = 2√2V K( V F − V K) V P is maximum voltage V K is nameplate knee point Voltage V F is knee Voltage with respect to stabilizing resistor V F = I SCLS( R CT + 2R L + R ST + R R) V F = 74.2( 0.52 + 0.042 + 41.7 + 1) V F = 3210V V P = 2√2V K( V F − V K) V P = 2 ∗ √2 ∗ 92( 3210 − 92) V P = 1514.88V
No Metrosil required, as maximum voltage must be greater than 3000V to install Metrosil.