1- Safety or protection of Air circuit breaker(ACB):

ACB is used between ratings as 400 Amp to 6300 Amp. It is available in thermal magnetic protection and microprocessor protection as overload, short circuit, earth fault.

A- Overload or long type (L):

Overload safeties are used in the air circuit breakers for the present load as per capacity. Load capacity can be adjusted as per the present load.
If the breaker capacity is 1000 A and the running load is 600 amp then the overload setting will have to keep 6.5.

1- Load pick up setting:

.4, .5, .55, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 1.0
Trip time is adjusted as per site or load requirement. Time setting details are given below mentioned.

2-Time delay setting :

it is available as- .5 second to 30 second.
.5, 1, 1.5, 2, 3, 5, 6, 12, 17, 30

B- Short circuit or short time (S):

Short circuit safeties are used in air circuit breakers for occurring a major fault like as phase to phase and phase to earth then a lot of current will be produced. So, the current value is multiplied by the breaker current rating.

1-Load pick up setting:

2 to 10 times or multiply of rating of current (Ir value).
2, 3, 4, 5, 6, 7, 8, 9, 10.

For Example:-
If the ACB rating is 1000 A Then we will have to set 3 to 4 times as default value.

2-Time Delay:

Trip time is adjusted as per site short circuit possibilities. Time setting details are given below mentioned.
it is available as 20 milliseconds to 600 milliseconds.
20, 60, 100, 120, 160, 200, 260, 300, 400, 500, 600.
Default time delay setting is 300 milliseconds.

C- Instantaneous short circuit (I):

If a fault is large then the air circuit breaker will be tripped quickly or instantaneously. No time delay is required for tripping because the fault is major.
So, the breaker will be tripped instantaneously .

1-Load pick up setting:

2 to 16 times or multiply of rating of current (Ir value).
2, 3, 4, 6, 8, 10, 12, 14, 16.

For Example:-
If the ACB rating is 1000 A Then current can be calculated as.....
2 x 1000= 2KA.
3 x 1000= 3KA.
4 x 1000= 4KA.

D- Earth fault (G):

Earth fault safeties are used in air circuit breakers for current leakage in the ground. It can be calculated as how many percent of leakage current is with the ground. It can be 20 percent to 60 percent.

1-Load pick up setting:

.2 to .6 multiply of breaker current rating (Ir value).
.2, .3, .4, .5, .6

For Example:-
Amp = 1000 A.
leakage current = 20%.
Calculation is: 1000 x .2 = 200 Amp leakage current.

2-Time Delay:

Trip time is adjusted as per site earth leakage possibilities. Time setting details are given below mentioned.
• It is available as 100 milliseconds to 400 milliseconds.
100, 200, 300, 400.
Default time delay setting is 300 milliseconds.

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