Low Voltage circuit-breaker breaking techniques - Schneider Electric

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VOLTA laboratory A3076 90/05/31/001.005 200.010 msreal assymmetryChannel 140 kAI1Channel 4205 VV1Channel 240 kAI2quasi-symmetryChannel 5204 VV2Channel 340 kAI3small loopChannel 6204 VV3Voltage wavesCurrent wavesFig. 15: oscillograms for test circuit breaking under three-phase a.c. voltage, with α = 0 (for phase 1).Cahier Technique Schneider Electric no. 154 / p.14
5.2 Breaking with limitationThe expression means that measures are takento prevent the short-circuit current from reachingthe maximum peak value of its prospectivecurrent (see fig. 16a ).This objective is an important one and in manycases vital if damage to the installation is to beavoided.Arc limitation is only possible if arcing voltagequickly becomes and remains greater thanmains voltage (cf. fig. 16b ).In fact, Ohm's law, e -R i-L di -Ua = 0, is useddtto define the three limitation conditions(see fig. 16c ):ccreation of an arcing voltage as early aspossible;aibuUaU aIpbroken itUrc increase of this arcing voltage as quickly aspossible to obtain Ua =e-R i and thus L didt = 0 ,which means that the current has then reached amaximum value îc;c holding this arcing voltage, Ua, at as high avalue as possible; di/dt is then negative and thecurrent is forced to 0.In short «Early, Quickly, High». Such is theslogan for :"Using the arc to break…prospective currents,…with limitation"ciîcFig. 16: limitation conditions.didt = 0 didt < 0tt5.3 Under DC voltageDC voltage takes the form u(t) = Ec Until the circuit is opened, current evolves asin the formula:E⎛ t ⎞ ⎛ t−⎞i = −R ⎜ ⎟ =⎜−−1 e τ Ip 1 e τ⎟⎝ ⎠ ⎝ ⎠c When the circuit is opened, an arcing voltageappears. If it increases rapidly, its overallevolution may be likened to a step function witha rising voltage defined by u a= E at an instant t 0(see fig. 17 ).The current, having reached a value i 0, thendecreases exponentially and disappears after atime ta
Page 3 and 4: no. 154LV circuit-breakerbreaking t
Page 5 and 6: LV circuit-breaker breaking techniq
Page 7 and 8: high, but ceases to be of any help
Page 9 and 10: a: composition of the arc columnb1:
Page 11 and 12: 3 Using the arc to break the curren
Page 13 and 14: c if U a = E then Wa/W L0 = 2 only!
Page 15: 5 Breaking prospective currents (wi
Page 19 and 20: 5.5 In a three-phase AC systemTwo c
Page 21 and 22: 6 The low voltage circuit-breakerA
Page 23 and 24: ⇒The contactsLV circuit-breaker c
Page 25 and 26: ⇒Arcing voltage when splitting oc
Page 27 and 28: ,,,-./012345:;c the former, reinfor
Page 29: 7 ConclusionThe future of the arc?T

Low Voltage circuit-breaker breaking techniques - Schneider Electric

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