Answer / prabhat kumar sinha, banswara

Whenever a Loaded circuit breaker is interrupted an arc is
inevitably formed between the contacts. But in the closing
time there is no current carrying by Circuit Breaker and no
any other effect on contacts. So, circuit breaker closing
time is always higher then tripping/opening time.

Answer / kevin

who the hell is this latika and s. karthik. i think they are non technical or does not have any basics of electrical. the first answer is the correct one

Answer / michael von zechlin

Neither of you are correct and for that matter who really
cares which is greater?
The opening and closing times of circuit breakers are
based on mechanical variables such as charging spring
tension, contact gap, trip mechanism delay etc. The goal
for a circuit breaker is to make or break the contacts as
quickly as possible to either slam the device on line or
open the contacts quickly enough to minimize the time that
an arc exists at the contacts.
What is significant are two measurements that provide an
indication of what the actual operating characteristics of
the circuit breaker are.
First, connect the contacts in series with one another
and a timer such that the circuit goes timer, 1st contact
set, 2nd contact set, 3rd contact set timer. (In one out
the other). Time the opening and closing of the circuit
breaker contacts. This will provide the fastest set of
contact make/break time.
Second, connect the contacts so that they are in
parallel with eachother record the value (This is the
average open/close time).
Once you have done this several times, say about 20,
take an average of each of the first/second measurement
times. Each manufacturer of circuit breakers has published
values for what those readings should be (average.
The significant readings of circuit breaker testing are
not usually related to the timing of the contacts, yes the
contacts can cause a motor to briefly single phase for less
than maybe 2 complete power cycles but not enough to really
matter, the significant measurements are those of mico-ohm
or millivolt drop across the contacts and closing spring
tension.

Answer / sam

i HAVE DONE THE TEST AND THE RESULTS ARE,( OPEN TIME-50,3ms
WHILE THE CLOSING TIME-72,2ms)

Answer / master

Closing time of the CB is 50 to 55 m.sec
Opening time is 35 to 40 m.sec
short opening time is minimizing the fault effect like arc

Answer / thayathidavan gopalan

Closing time is always greater than opening time.Closing a
breaker means you have to close against the inertia and it
is closing on no load normally.
Opening time should be fast as possible to interrupt the arc
fast to avoid damaging of the contact , It depends upon
the manufacture and design of driving mechanism ,make to
open as fast as possible.

opening during fault shall be as fast as good to maintain
system stability also

Answer / abhishek goyal

Whenever Loaded CB is interrupted during running time it
generate arc at CB contact area. If some fault happening
during running it will damage the electrical equipment so we
need to fast action to reduce damage or risk (for ex: Short
ckt and over voltage etc.).
At the closing time there is no current drawn by CB contact
So that, circuit breaker closing time is always higher then
tripping/opening time.

second reason of slow closing time for contact to reduce
damage or risk of contact tips or other parts (MAY be
manufacture point of view)

Answer / robert

when closing the breaker u are also charging the spring

Answer / btln

The circuit breaker closing time depends on the mechanisim
of the circuit breaker,normally the opening time should be
less to trip the breaker in short time to prevent the exess
arcing of the contats else it may damage the interrupter
during the arcing period.and for closing time the circuit
breaker mechanisim will take longer time to close the
breaker and it will be maintained with effective load with
contact loading springs to prevent pre arcing.

Answer / krishnakumar

The circuit breaker is used for protection purpose and the main function is to trip(open its contacts) when relay gives the trip command.the tripping of breaker will isolate the healthy phase from faulty phase.if the tripping time is more t,then the fault will be present for more timing and this will damage the whole system.so the breaker should operate at high speed in order to protect the system.so,the tripping timing should be less.but in case of closing of breaker,there is no need as such as tripping at fault condition.and there is another phenomenon called bouncing that makes the timing increased than tripping time.if the timing is less for closing,then the breaker moving contact moves very fast towards the fixed contact and so the bouncing will be more due to the high speed.this is also a reason for more closing time

My question is whether bellow formula is correct to find bus size for 46kA for 0.5 second & what is RT in bellow formula. formula to calculate the size of busbar to withstand the thermal stresses due to currents with duration of 0.2 sec to 5 sec. Sp = RT( I x I x t) / K Where Sp – is the cross sectional area of bus bar in millimeters. I -    is the value of AC fault current. t -    is the operating time of disconnecting device in seconds. K –  is the factor depending on the material of the conductor, insulation and initial and final temperature. Value of ‘k’ for copper is 143.

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