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To limit cur rent chopping in vacuum circuit breakers, the contact material used has
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- high vapour pressure and low conductivity properties
- high vapour pressure and high conductivity properties
- low vapour pressure and high conductivity properties
- low vapour pressur e and low conductivity properties
Correct Option: D
In vacuum CB, the current chopping depends upon the vapour pr essur e and the electr on emission property of the contact material. Ther efor e, to reduce the current level for chopping to occur, a high vapour pressure and low conductivity metal is desirable, since gas pressure is low in a vacuum switch. A low conductive material will maintain contact surface temperature and vaporization for a longer time to maintain the arc stability which is necessary for current chopping.
