Breaker Long Time Delay

Nice reference.

I read that but I am not clear yet.

The long time delay is supposed to make the relay wait for 20s. Then why it trips in short circuit?

A <...short circuit...> will be well over either setting. One needs to protect the wiring!

Yes, it is OR LOGIC. This or that to trip.

Safe limit is not feasible to be over ridden if it is inbuilt.

Adjustable circuit breakers come with current ranges for each time duration. Trip time depends on the current flow.

In this example the log time trip curve is applicable for 1 to 12 times tripping current and takes from 1 to 10,000 seconds. Short time applies for 12 to about 30 times tripping current, taking roughly .02 to 1 second, and instantaneous trip applies for fault currents over 12 to 30 times tripping current in less than .06 seconds and usually in less than 3 cycles of the current. The overlap of short and instantaneous trip times seems a little confusing, but in marginal current for very short duration faults don't always result in an annoyance trip. It allows the squirrel to explode and clear the fault without blacking out Los Angeles.

The short time pick up range is 1.5 to 10. As per your suggestion, under which condition i can choose the ranges from1.5 to 6? Because long time delay is fixed at 6×In. I can not manipulate it.

The pick and delay for short time OC protection is selected based on the coordination requirements with the downstream device(s).

Once downstream device protection curve is finalised, the upstream device curve can be adjusted as required for appropriate coordination.

Protection devices are never set in isolation, either you have an equipment whose characteristics are to be known for giving appropriate settings for the protection device or a downstream device with which coordination is to ensured.

Where is the user manual for the breaker, please? The manufacturer's phone number will be on it.

The circuit breaker trip settings describe a curve on a log-log10 time vs. current plot. the individual settings are used to adjust the curve position and shape. You have to combine the settings to see the final shape of the curve.

The long time curve will have an inverse shape (time decreases smoothly as current increases). You set the pickup current value (In = 1000A) as the start of the curve, at which point the time will be maximum on the plot. The long time delay then gives you a point on the curve that you can aim to, so that at 6 x In, the time will be 20 seconds. If you continued the curve onward, at 10x you may 5 seconds, etc.

The short time curve starts at the point you set, which is 5 x In. If you find on your plot the current value of 5 x In (= 5000A), draw a vertical line downward from that point on the long time inverse curve, until you get to the time of 0.4 seconds. At that point the curve will stop and turn horizontal. Any increase in current above 5000A will still trip in 0.4 seconds.

If there is also a higher, instantaneous trip setting, that will intersect the short time horizontal curve and do the same vertical/horizontal plot as the short time, except at the higher current and shorter time (no intentional delay).

You can see a good example of this plot in the link provided by Solar Eagle (Good answer for him!).

It is incorrect practice to use a <...circuit breaker...> to carry out <...motor starting...>.