Answer / pratik

Since breaker operates in transiant state & it is design to
pass the sub transient current through it.But it is
supposed that if breaker is just about to close & fault
occurs at the same time then breaker will have to close in
that sub transient period & thus amount of arc produce will
be very high.Thus making cap. is very high.

Answer / zeeshanm

*When breaker is closed and a fault occurs then it closes
in transient state(in transient state DC offset become zero)
so the current capacity at this intant is only the rms
value of current(symmetical component)in transient state
which is also called breaking capacity of breaker.i.e
Breaking capacity=rms value of breaking current in
transient state.

* Now when breaker is going to be closed and mean time
fault occurs then it will close in sub transient state and
the current carrying capacity at this instant contains rms
value of current (~symmetical componentin transient state)
and the DC offset current in subtransient state which is
also called Making capacity of breaker.i.e
Making Capacity=DC offset current+rms value of breaking
current in transient state

Therefore: Making capacity > Breaking Capacity

Answer / solanki

guys ryt answer is that making capacity used the peak value
of current while breaking capacit work on the rms value of
current thatswhy making capacity is more than breaking
capacity......

Answer / avdhesh

I think Pratik has given the exect answer. I wish to add
one more thing during closing of a circuit breaker. When we
close the breaker, there is rebounses of the contacts( 5-6
rebounces are normal in VCB). During transient state (Plus
fault) there is a chance of melting and welding of contacts
hence breaker making capacity is always required high.

Answer / vivek malhotra

Suppose the breaker is closing and at the same time a fault
occurs, then at that stage the arc will be very high due to
inrush and short circuit. But in case of breaking a circuit
when current is already flowing, the arc produced is less
as compared to during making of a circuit.
Hence the making capacity is always greater than breaking
capacity

Answer / dipak

Here I want to add to Pratik answer. During fault, say on EHV line, line protection sense the fault and gives trip command to CB. The time involved from detection of fault to opening of CB(including response time of trip relay and CB opening mechanism) is about 30 to 40 msec. By this time, Sub transient and DC component of fault current get damped and CB actually get open in transient component of fault current.
However, during closing of CB, if fault is there on line(say dead fault), CB has to sustain Sub transient fault current during closing on dead fault. Hence, making capacity is always more than breaking capacity.
Also, CB is designed for considering its application as Generator CB because fault level is highest at generator terminal and therefore higher making and Breaking capacity is required for Generator CB.

Answer / tapeshwar pandey

The making capacity is more than the breaking capacity to
maintain the RRV.

Answer / pallav jain

Tapeshwar what is rrv.?

Answer / ashish

pratik ur absolutely right but i m not able to know why this
site has given u the zero mark but ur ans was correct so
everyone can go through dis.

well done........be ready for ur next que

Answer / borys nijinski

The breaking capacity is less than make because make does
not require the arc to be extinguished. When the contacts
open, with current flowing, there is an arc created and
that arc needs to be extinguished. Extinguishing the arc
can be achieved by lengthening the arc (arc chute and air
puffer) or through an environment that does maskes the
creation of arcs difficult (eg SF6). AC arcs are much
easier to extinguish because the voltage passes through 0;
DC arcs are much harder to extinguish which is evidenced by
the lower rating of break capacity with DC as opposed to AC
for the same contactor/breaker.

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