Page 688 - Industrial Power Engineering and Applications Handbook

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boiling point, the vapour
is largely composed of
copper ions
3 Theory of arc Cooling of arc plasma is based on the bubble theory, Deionization of N, (0, Deionization of N, and Deionization of free Deionization of copper
quenching and H, cooling it by the turbulence caused by H2 bubble having a small content, has 0, by a strong blast of sulphur electrons S", ions is natural and extre-
extinction, through no significant influence) air. The deionization takes place through their mely fast
deionization of arc by lengthening of the arc force remains the same absorption by the
plasma plasma through the arc for one size of breaker, fluorine ions F
chutes, as a result of mag- irrespective of the (electronegative theory)
netic field induced in the current
metallic splitters of the arc
chute by the inductive arc
plasma
4 Number of no-load Min. 1000 Min. 1000 Min. 1000 Min. 1000 Min. 5000 Min. 10 000-20 000
operations (depends
uponthearcenergy: the
lower the arc energy,
the higher will be the
number of operations
and vice versa).
5 Maintenance High, to check the con- Checking the condition of Very low maintenance except for checking the Requires very little Requires very little
dition of oil, contacts and oil is more frequent, in condition maintenance, except maintenance, except
arc quenching tins and view of smaller quantity of the arcing contacts for any wear, tear or pitting periodic checks of periodic checks of
devices of oil pressure and condition vacuum and condition of
of the contacts the contacts. Maximum
contact erosion 2-3 mm
6 Dielectric strength > 2 >2 1 Compressed air has better 2-3 Nearly 10 times (5 times
compared to air than 1 of oil)
I
I
7 Arc energy compared 1 1 - - Roughly - (Figure 19.6) Roughly - (Figure 19.6)
10
3
to oil
(Contact erosion low and suitable for frequent
operations)
8 Whether suitable to Yes (but for a limited No, because of generally On an LT system, such a No, bccausc of force of Yes, in all types of arc- Generally not, because
interrupt small number of switching one break per pole, for phenomenon has no air blast even at small quenching techniques: of extremely fast
inductive operations), because of breakers 12 kV and relevance, because of currents which may (i) Puffer type: because deionization. It has the
(magnetizing) or double break per above, unless the breaker high dielectric strength develop the tendency to the flow of gas tendency to current
capacitive currents, phase that enables quick is specially designed between the parting current chopping. On the through the arc is a chopping. However, in
without causing restoration of the with extra quenching contacts compared to the other hand, it is possible function of magni- view of continuous
current chopping dielectric strength system through a jet of system voltage that the breaker may fail tude of current development in this
oil to interrupt the steep (ii) Rotating arc type: field, it has now been
fronted TRVs because the possible to achieve a
magnetic field that chopping current as low
(Confd)