ETAP LV Circuit Breaker Opening Times

[bdfig]

Hi all,

In ETAP I have added LV circuit breaker opening times in the "Min. Delay" field under the Ratings Tab. However the opening times do not appear in the sequence of events or arc flash study results, and the arc flash fault clearing times appear to just use the trip device TCC time at the fault current. Any advice is appreciated.

(I have a HV circuit breaker controlled by a relay, where I have entered the opening time under "Min. Delay" and this appears to be working correctly in the sequence of events and arc flash study results)

 

[dpc]

Time current curves published by manufacturers for low voltage circuit breaker should include all tolerances and also breaker opening and arcing time. There is no need to add any additional time. This is not the case for high voltage breakers controlled by protective relays.

I don't use ETAP, but presumably the breaker opening time is added in only for medium and high voltage breakers and this includes the "min delay" variable as well.

 

[bdfig]

Hi dpc, is this also the case for electronic trip units? Specifically I am looking at curves from PR222DS/P trip units for ABB T4S and T5S circuit breakers, and PR331/P trip units for ABB T7H circuit breakers.

 

[dpc]

Yes, the curves for the electronic trip units should include the breaker operating and clearing time. At least in my experience. That is why there sometimes different trip unit curves for the same trip unit applied to different breakers.

 

[tims924]

Here is what I have seen in the past.

The SKM Software has limitations that do not allow these delays to be entered under the following conditions.

The two cases where you cannot change the breaker opening time in the arc flash evaluation:
1.) The fault current contribution is coming from an induction motor set within the Options menu to clear in a specified number of cycles.
2.) The maximum arcing duration has already been reached. Either because:
a. The protective device that is supposed to trip that portion of the arcing fault current is set above the maximum arcing duration.
b. You do not have a protective device to clear the arcing current.

I am wondering if you meet one of these two condtions and therefore they are not taken into account.

For the Arc Flash studies I perform I assume the following:

molded case circuit breakers would take 0.025 seconds to open once a fault occurs and 0.050 seconds for power circuit breakers in the switchgear.