Use of Breakers

HT breakers for HT lines; LT breakers for LT lines. Local Codes may have different distinctions between high voltage/tension, medium voltage/tension, and low voltage/tension. The higher the voltage, the thicker the insulation and/or the wider the separation between conductors; also larger arc gaps for switching components.

From your name, I assume you are from India. And, as per the Indian Electricity Rules, 1956, Rule No. 2 (av):

Low Voltage is not exceeding 250V

Medium Voltage is not exceeding 650V

High Voltage is not exceeding 33000V and

Extra High Voltage is exceeding 33000V

And, a breaker which is used in High Voltages is called HT Breaker and a breaker which is used in Low Voltages is called LT Breaker. So also for the HT and LT Lines.