interrupting time poll

No response to the first thread. Perhaps a poll will collect more?

Based on IEEE C37.04 section 5.6, do you add an extra half or full cycle to to your breaker rating when figuring IE?

Maybe if you quoted the referenced section and the title of the standard. I can't find a C7.05 in browsing through IEEE Xplore. I also can't find a C37.05.

I said other because we now try to base our studies of first trip data, not a table that says when it "should" trip.

Sorry, corrected in the body; but I see no way to correct the question.

"5.6 Rated interrupting time
The rated interrupting time of a circuit breaker is the maximum permissible interval between the energizing
of the trip circuit at rated control voltage and rated operating pressure for mechanical operation, and the
interruption of the current in the main circuit in all poles. The interrupting time for a close-open operation
shall not exceed the rated interrupting time by more than 1 cycle of rated power frequency for circuit breakers
with interrupting times of 5 cycles or more, and 1/2 cycle for circuit breakers with interrupting times of
3 cycles or less. (Cycles are based on corresponding rated power frequency.)"

Please note that the adder is for a CO operation. This is a close into fault situation.

Zog,

Please explain. Where do you get "first trip data?"

Breaker rated interrupting time is not used?

I never suggested using a table.

Table, software database, whatever, all the same, not real values. Not trying to pick on you though, most people are still doing it with published data. The future of accurate studies is first trip data. (Google it and you will see all the articles, gathering a lot of steam in the testing world).

(The following is reposted from a NETA world article by my co-worker, Don Genutis)

Typically, circuit breakers remain dormant for very long periods of time, but when called upon to interrupt a fault, they are expected to operate within finite times based upon their protective settings. These settings are derived by conducting coordination and arc-flash studies to optimize electrical system performance and enhance worker safety. Typically, the breaker’s lubrication conditioncchanges over time, due to a number of factors, and hardens to a point where the breaker’s first trip is inhibited. This first trip represents the breaker’s true operating time and often differs greatly from the values expected in the studies thus adversely affecting system performance and exposing the worker to higher levels of incident energy and making the studies invalid.

The only solution to validate the studies and to protect the worker is to frequently verify breaker timing under first trip conditions. Typical maintenance and testing occurs after the breaker has already been tripped once, and thus the critical first trip condition information is lost. Regular exercising of the breaker can help the first trip performance. Frequent maintenance will also help, but these activities do not ensure optimum first trip operation.

A new technology has evolved that efficiently determines breaker first trip performance thus enabling validation of the arc-flash study. This technology has the additional benefit of verifying overall breaker mechanical condition. A special transducer is magnetically coupled to the front of the breaker ,after the technician moves from the exposure zone, the breaker is operated. The
transducer sends valuable vibration signals that represent breaker first trip timing and mechanical condition to a handheld analyzer. This unique breaker vibration signature is compared to a database library of known signatures.

Post test analysis can include superimposing the test breaker signature upon good breaker signatures to quickly spot potential problems. Should the breaker fail the first trip test in the field, it is necessary to perform complete shop reconditioning or remanufacturing in order to return the breaker to a condition that will ensure proper operation and validate the arc-flash study. Frequent performance of the breaker vibration signature test ensures performance and exercises the breaker mechanism.

Here is a link to the full article, http://www.nooutageelectricaltesting.com/PDF/no-outage-safety.pdf

Zog,

Seems to be a verification of the breaker mechanical operating time. Not sure how you get from there to the interrupting time. A "first interrupting time" test would require a source capable of supplying rated interrupting current to the breaker. I think I'll leave that to the manufacturers. And we seem to be considering only an open after a long time closed, just the opposite of my suggestion to use the CO extra half or full cycle.

You can have the fastest relay in the world but if the breaker will not open in the assumed time it does you no good. We simulate they fault curent via secondary injection with the breaker still in the cell. Primary injection can only be done after the breakr is removed from the cell and is still done to verify the CT's are operating correctly after the first trip data is recorded.

First trip is the future of breaker testing and arc flash studies, stay tuned.

Zog,

Secondary injection does not emulate the way primary fault current is cleared. You can have the fastest breaker mechanism in the world, and it will do you no good if the current continues to arc across the contacts for very long.

And primary injection test sets cannot provide sufficient current/voltage to emulate a real fault.

Clearing time = relay time + interrupting time.

Interrupting time = opening time + arcing time.

For an illustration see C37.010 Figure 2. I fear your method is neglecting the arcing time.

If I understand the standard correctly, the extra time would only apply when closing into a fault. In this case, the actual arcing time at the fault location will be less than the CO time of the breaker. Before the breaker is closed, there is no voltage at the fault location and no arcing. To close into a fault would mean that the fault would either be bolted to start with (no gap) or have a very small gap that would arc over after energization. It could develop into an arc across the assumed gap distance, but only after some finite time.

I voted for using interrupting time plus relay time.

Not at all, still factored in, but our method is finding the real opening time, not the assumed opening time.

Then the arcing time is the remaining assumption. How do address this value?

Opening time is dependant on the mechanical condition of the breaker and will change over time, arcing current is not and depends on the calculatable properties of the system.

Zog,
We seem to have a failure to communicate.

I asked about arcing time, not current. This is the time from initial pole opening until the fault is cleared. (This arc is that which occurs inside the breaker interruption chamber, not the arc flash event at the fault location) Your breaker timing test does not include this piece. How do you account for it? By the scaling of C37.010 Fig.2, the arcing time makes up more than half the interruption time.

But the opening time is the variable here. I think we are not communicating well, but we are thread jacking. ABB and GE are both using similar technology and there are many white papers on first trip technology available by people more involved in it than I am .

I for one do not think you are thread jacking.....why not go forward and see where it leads?

I also voted for relay time + rated interrupting time. This is based on the interrupting time being the total contact parting plus arcing time.

Seems to me that the CO requirement is a specific equipment design test.

If we have to assume the breaker will not operate as advertised, then shouldn't we also assume that the relay won't either....and, if so, where does it end?

And I have to "ponder" what has happened to the downstream fault once we start the arcing in the breaker?

Zog,

I also think this is a worthwhile discussion that should continue. If you consider arcing time to be constant, what constant do you use and where do you get it from?

I must also question that opening time is the only variable. If first trip measurement finds a slow opening time due to a slow mechanism, the arcing time will also likely be extended as it will take longer to get from contact parting to the point where the arc is extinguished.

Good point about the arcing time, I will have to ask our first trip guru about how they handle that one.