Long time delay band on circuit breakers

[adamscb]

All,

I'm trying to gain a better, more in-depth understanding of breaker trip curves, and with I2T OUT I have no problem, however it's with I2T IN that I start struggling. With I2T OUT on both the short and long time settings, I'm knowledgeable enough now where I can see the TCC in my mind. However, when I2T IN, I'm having a hard time visualizing what it looks like.

For example, what are the long time delay and short time delay values shown on page 3 of this document?

http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf

 

[jim dungar]

The Long Time Delay is that portion of the curve between the Long Time and the Short Time bands. Look at the portion covering 5X @100Sec.
The Short Time Delay is that portion of the curve between the Short Time and the InstantaneousTime bands. Look at the portion covering 7X @1Sec. Notice how the slope of this delay goes to Zero when using the I2T OUT setting.

 

[adamscb]

The Long Time Delay is that portion of the curve between the Long Time and the Short Time bands. Look at the portion covering 5X @100Sec.
The Short Time Delay is that portion of the curve between the Short Time and the InstantaneousTime bands. Look at the portion covering 7X @1Sec. Notice how the slope of this delay goes to Zero when using the I2T OUT setting.

So just by looking at that curve, what would you estimate the long time and short time delay settings are when I2T is IN?

 

[jim dungar]

So just by looking at that curve, what would you estimate the long time and short time delay settings are when I2T is IN?

The Long Time Delay value is not dependent on the I2T being either IN or OUT.
There is no way to estimate the actual delay settings as those are dependent on the breaker's trip unit.

 

[topgone]

So just by looking at that curve, what would you estimate the long time and short time delay settings are when I2T is IN?

As posted above, tripping time depends on In (continuous rating setting) of your breaker. Here's a computation method on how to arrive at total clearing time with I²T -IN:
tc sd max = (((1.2 x 12 x I_n)² x (t_sd + 0.05))) / i² + 0.065
tc sd min = ((12 x In)² x t_sd) / i² + 0.035

; where t_sd = Short time delay setting (seconds) and
I_n = Continuous current rating, as defined by the rating plug (amperes)​

 

[Sahib]

As posted above, tripping time depends on In (continuous rating setting) of your breaker. Here's a computation method on how to arrive at total clearing time with I²T -IN:
tc sd max = (((1.2 x 12 x I_n)² x (t_sd + 0.05))) / i² + 0.065
tc sd min = ((12 x In)² x t_sd) / i² + 0.035

; where t_sd = Short time delay setting (seconds) and
I_n = Continuous current rating, as defined by the rating plug (amperes)​

It also depends on fault current i.

 

[Sahib]

It also depends on fault current i.

It does not with I2T-out on.