Surge voltage protection arrangements

Claim 2

A circuit arrangement comprising: a load, which is connected across a periodic A.C. supply, and a surge voltage protection arrangement for the load, said surge voltage protection arrangement comprising a gas-filled excess voltage arrester, a capacitance connected in series across the load and a resistance connected in parallel with the capacitance; the arrester constituting the sole voltage arrester of the surge voltage arrangement and starting to conduct at a voltage greater than that at which it will extinguish; and the capacitance having a value such that, with the arrester conducting and the A.C. supply voltage applied across the load, the capacitance charges substantially to the instantaneous value of the supply voltage, thereby extinguishing the arrester in a fraction of the A.C. supply period.

Claim 3

A circuit arrangement according to claim 1, wherein the values of the capacitance and resistance are such that the capacitance is able to discharge through the resistance within one half cycle of the A.C. supply.

Claim 4

A circuit arrangement according to claim 2, wherein the capacitance has a value of not less than 10 microfarads.

Claim 5

A circuit arrangement according to claim 1, wherein the resistance has a value of not more than 500 ohms.

Claim 6

A circuit arrangement according to claim 4, wherein the capacitance has a value of not less than 10 microfarads.

Claim 7

A circuit arrangement according to claim 1, wherein the capacitance has a value of not less than 10 microfarads.

Claim 8

In an A.C. circuit wherein an A.C. supply is connected across a load for supplying a periodic A.C. supply voltage thereto, a surge voltage protection arrangement for protecting the load from a surge voltage, said arrangement comprising: (a) a single gas-filled excess voltage arrester having spaced-apart electrodes and fireable from an extinguished state, in the event of a surge voltage, to a conducting state in which a surge current is conducted between the electrodes, the voltage at which said arrester fires being greater than that at which the arrester recovers from its conducting state to its extinguished state; and (b) means for causing the arrester to rapidly recover from the conducting state to the extinguished state in a fraction of a period of the A.C. supply voltage, said means constituting a capacitor connected in series with the arrester, said capacitor and said arrester together being connected in parallel across the load, and a resistor connected in parallel with the capacitor, said capacitor charging substantially to the instantaneous value of the A.C. supply voltage when the arrester is in the conducting state, and said capacitor having a predetermined capacitance value such that, after the cessation of the surge voltage, (i) the arrester rapidly recovers from the conducting state to the extinguished state within said fraction of said period, and (ii) the surge current ceases within said fraction of said period before the surge current damages the electrodes of the arrester, thereby increasing the reliability of the arrester in the A.C. circuit, and said resistor having a predetermined resistance value such that after the cessation of the surge voltage, the capacitor discharges through the resistor within one half cycle of said period of the A.C. supply voltage.

Claim 9

In an A.C. circuit wherein an A.C. supply is connected across a load for supplying a periodic A.C. supply voltage thereto, a surge voltage protection arrangement for protecting the load from a surge voltage, said arrangement comprising: (a) a single gas-filled excess voltage arrester having spaced-apart electrodes and fireable from an extinguished state, in the event of a surge voltage, to a conducting state in which a surge current is conducted between the electrodes, the voltage at which said arrester fires being greater than that at which the arrester recovers from its conducting state to its extinguished state; and (b) means for causing the arrester to rapidly recover from the conducting state to the extinguished state in a fraction of a period of the A.C. supply voltage, said means constituting a capacitor connected in series with the arrester, said capacitor and said arrester together being connected in parallel across the load, and a resistor connected in parallel with the capacitor, said capacitor charging substantially to the instantaneous value of the A.C. supply voltage when the arrester is in the conducting state, and said capacitor having a predetermined capacitance value such that, after the cessation of the surge voltage, (i) the arrester rapidly recovers from the conducting state to the extinguished state within said fraction of said period, and (ii) the surge current ceases within said fraction of said period before the surge current damages the electrodes of the arrester, thereby increasing the reliability of the arrester in the A.C. circuit, and said resistor having a predetermined resistance value such that after the cessation of the surge voltage, the capacitor discharges through the resistor within one half cycle of said period of the A.C. supply voltage.

Claim 10

The protection arrangement according to claim 7, wherein the resistance value is not more than 100 ohms, and the capacitance value is not less than 10 microfarads.