First pole to clear factor

There had been a number of discussions and threads in this subject.

Since you are new entrant, you might not be aware, try to use the Right side box (Search this forum) and type in the keywords.

Also use search engines to search nets. Only when there is dearth of data, ask in forums.

In simple terms it is the voltage(rms) between the faulted phase and unfaulted phase / phase-neutral Voltage during no fault condition.

As you are aware the three arcs in breakers do not extinguish together. So the first one that extinguishes has to tajke the full stress (the other poles being still connected by the arc)

In AC circuit breaker, the zero point of current is used to extinguish the arc for clearing the fault. As because the zero point of three phase system doesn't occur simultaneously, the arc of all the three poles is not cleared at same moment. The pole which clears the arc first experiences the higher TRV (Transient Recovery Voltage, see http://en.wikipedia.org/wiki/Transient_Recovery_Voltage). The first-pole-to-clear-factor (kpp or K3) is used for calculating the transient recovery voltage for the faults in three-phase system.

Kpp = Rms voltage between healthy phase to faulty phase / Phase to neutral voltage with fault removed.

Its value depends on the earthling system of the network. In general the following cases apply:

- kpp = 1.0, if both neutral and fault are earthed

- kpp = 1.5, if either neutral or fault is not earthed

See the following Google Book link for calculating TRV from Kpp:

http://books.google.com/books?id=0nyD0Av7pakC&pg=RA1-PA22&lpg=RA1-PA22&dq=first-pole-to-clear-factor&source=bl&ots=QQ2OmCbUNL&sig=7D1SHROFx2JGT1tRHm81JNc2RtY&hl=en&ei=z6oGS_n2IoPUnAeu5tnICw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CB0Q6AEwBzgK#v=onepage&q=first-pole-to-clear-factor&f=false

-MS