iso later quarries

Not much without some idea of what the isolator is doing.

When any switchgear breaks a low reactive current, there will be huge re-striking voltage (As arc quenching happens at current-zero and because of the almost zero power factor, the voltage at the instant of current-zero will be maximum). This peak voltage will try to re-strike the arc acorss the opening terminals of the switchgear. The switchgear shall be able to withstand this condition too and the di-electric strength across the opening terminals of the switchgear shall build up so fast that there shall not be re-strike of arc due to the high re-striking voltage.

@electricalexpert65

Would you please elaborate your answer?

Please help.may send the details in my email Id also

saraswatapalit@yahoo.com

best regard

First, you should understand the principles of arc quenching in any switchgear. As the switchgear breaks a current, an arc is struck between the fixed contact and the parting moving contact, the strength of the arc in square proportion to the current being broken. And, in AC circuits, when the current goes thro a zero (as it happens in every half cycle), this arc strength also becomes zero. But at the same time, there would also be a potential difference between the fixed and the moving contacts, which would try to re-strike the arc and this potential is optly called "Re-striking Voltage". Further arc strike is avoided by the rapid build-up of the dielectric (insulating) medium between the fixed and the moving contact. The dielectric medium could be Oil (as in BOCB/MOCB), Vacuum (as in a VCB) or SF6 (as in a GCB).

Had the current been resistive, no problem whatsoever, as current and voltage would be in phase and both would go to zero at the same instant. (i.e.) when arc ceases at the nearest current zero, the voltage is also at its zero thereby avoiding any re-striking voltage. Arc gets quenched easily.

Whereas, in reactive loads with low power factor, when current is zero, voltage is at its maximum. So, when arc strength is nil at current zero, the re-striking voltage will be at its peak, trying to re-strike the arc across the parting contacts with full force. The arc quenching medium has to overcome this "full strength" re-striking voltage and still would build up the di-electric strength acorss the contacts.

Hope it is clear.