Low Voltage circuit-breaker breaking techniques - Schneider Electric

c if U a = E then Wa/W L0 = 2 only! But breakingtime is infinite!c if U a is very big or even infinite then:Wa/W L0 =1.Arcing energy is equal to initial inductive energyand breaking time is virtually zero: arcing powerWa/t ais very high!c that the "bend" of curve Wa/W L0is a practicaloptimum and thus that the value :Ua15 , < < 2,5Eis a good compromise; thenWa ≈ 1.2 W L0 and t a ≈ τ.The coefficient 1.2 (read on the bend) is verysatisfactory due to its proximity to the "1"minimorum minimum, difficult to reach.4.2 In AC single-phase supplyu = E sin ωti = I 0 cos (ωt + ϕ), withcos ϕ=L ωL ω + R 2( ) 2Eand Ι 0 =2 2LωR( ) +The arc appears as soon as the contactsseparate, and evolution of its voltage in time mayappear complex. However u a still has the sign of"i" and its mean absolute value tends towards Ua(see fig. 9 ).The mathematical study of i a , t a and Wa, basedon extended Ohm's lawu-Ri-Ldi/dt - u a = 0 is still possible but not soeasy.Moreover, since these calculations do notconsider the voltage recovery conditions of reala.c. breaking, the two cases U a ≥ E and U a