The maximum economical voltage range for a vacuum circuit breaker is:

The maximum economical voltage range for vacuum CBs is 36 kV.

Vacuum Circuit Breaker

• A breaker that used a vacuum as an arc extinction medium is called a vacuum circuit breaker.
• In this circuit breaker, the fixed and moving contact is enclosed in a permanently sealed vacuum interrupter.
• The arc is extinct as the contacts are separated in a high vacuum. 
• It is mainly used for medium voltage ranging from 11 KV to 33 KV.
   

The vacuum circuit breaker has mainly two phenomenal properties:

• It has high insulating strength in comparison to various other insulating media used in circuit breaker vacuums and is a superior dielectric medium. It is better than all other media except air and SF6, which are employed at high pressure.
• When an arc is opened by moving apart the contacts in a vacuum, an interruption occurs at the first current zero. With the arc interruption, their dielectric strength increases up to a rate of thousands of times as compared to other breakers.
   

The above two properties make the breakers more efficient, less bulky, and cheaper.