question on impulse voltage

Perhaps you could explain your question more fully.

1. Is it an "Air Blast Circuit Breaker", which has several switches in series, each opened by a blast of compressed air at 600+ psi?
2. Is it a circuit breaker operated by a motor ?
3. Is it a circuit breaker operated by a solenoid ?
   
4. What is the normal operating voltage of the circuit breaker ?
5. Is the circuit breaker for EHT, HV - because the design of these is quite different from mains voltage breakers.
6. Is it single or 3 phase supply ?
7. Is the breaker switched voltage AC or DC ?
   
8. Are you referring to the peak impulse voltage that the Air circuit breaker can withstand, in the open position, before breaking down ?

The answers to the above may assist in your getting a useful answer.

it is a air circuit breaker,normal operating voltage is 440 that means low voltage breaker,i want increase impulse voltage from 9kv to 12kv

it is an "Air cicuit breaker" operated by motor,Normal operating voltage is 415v,it is low voltage swithgear product,supply is 3 phase,operated on AC

Hello again Pravin,

You didn't answer the necessary questions(renumbered from my first reply)

1. Is it a circuit breaker operated by a motor ?
2. Is it a circuit breaker operated by a solenoid ?
   
3. Is it single or 3 phase supply ?
4. Is the breaker switched voltage AC or DC ?
   
5. Are you referring to the peak impulse voltage that the Air circuit breaker can withstand, in the open position, before breaking down ?

If you are hoping to "increase impulse voltage from 9kv to 12kv"

and that means the "breakdown voltage" (see (5) above in THIS Post, of the Circuit breaker,then you can only increase that "Impulse Voltage" by re-designing the Circuit Breaker.

That means you then have a different Circuit Breaker, it is not the same Circuit Breaker, but a different model, although some parts (common parts) may still be able to be used.

Also you did not state the normal Current, trip current,and maximum short circuit current expected through the Circuit Breaker - these need to be stated,so that your question may be properly answered.

Relative Humidity at the location of the Circuit Breaker is very important, as higher humidity levels de-rate the peak impulse voltage ....

it is air circuit breaker operated by motor(only charging and discharging),it is a 3 phase acb,short circuit withstanding capacity is 80 KA,normal current is 1600 A.

Hello again pravin,

There is not any practical way you can increase the maximum impulse on that breaker from its present 9kV to the 12kV you say you need.

If you need a 12kV impulse voltage Circuit Breaker, to handle the ordinary voltage plus current/peak current as stated, you are best to purchase one with that specification.

Why is the impulse voltage changed from 9kV to 12kV ?

Dependent on your network where you intend to use the Circuit Breaker, you could use "surge limiters", which can be specified to limit the maximum impulse voltage across the Circuit Breaker at 9kV, so the Circuit Breaker is not destroyed.

These "Surge Limiters" work by acting within a nanosecond or two, at any voltage exceeding their "rated Maximum", they act as a "snubber" to the excess impulse voltage, shunting the excess voltage to the Earth/Ground connection.

Surge Limiters may often be seen where 400V or 11kV reticulation is by aerial power lines, at the change from overhead to underground cables, and thus keep induced "Lightning Surges" from entering the cable.

If the induced "Lightning Surge" enters an underground cable, it destroys it, by arcing quickly along its length, like a giant firework display, exploding the cable soil covering upwards, because of the sudden gas/steam generation - very spectacular if you are close enough to see it, and survive the earth currents)

Hope that helps you, if you need further assistance, reply here.....