Page 687 - Industrial Power Engineering and Applications Handbook

Table 19.1 Comparison of interrupting devices

VCB"
I 2 7
-
I Specification\
Mcditini of Oil Oil Air Air blast Sulphur hexallutri-idc Vxuum
insulation and
quenching of arc
plasma
Nominal voltage
ratings
HT 3.3-200 kV 3.3-470 kV and above Up to 22 kV I 1-765 kV 6.6-76.5 kV and above 3.3 hV to 30 k\i
(not in practice in light
of bettei- technologies in
VCB's and SF6)
LT 66OV Not economical 660 V Not applicable Not applicable Not applicable
(iii) Nominal current Manufactured in all Only one break per pole, Up to 6000 A Up to 4000 A and higher Up to 4000 A and highcr A\ required
ratings possible current ratings therefore current ratings
in higher ranges are
restricted
(iv) Closing time 5 cycles 4-6 cycles 1-2 cycles 2-3 cycle? 4-5 cycles 2-3 cycles
(between the instant
of application of
voltage to the
closing coil and the
instant when the
contacts touch)c
(v) Opening time
(between the instant 4-5 cycles 2-3 cycles i-l cycle 1-2 cycles 1-2 + cycles 1-2 cycle.;
ofapplication of
voltage to the trip
coil and the instant
of separation of the
arcing contacts)'
(vi) Maximum duration 0.75-1.25 cycles 2 cycle\ +-1 cycle 1-1 + cycle i-I cycle
of arc plasma (arcing
time)'
(vii) Total breaking time 4.75-6.25 cycles 4-5 cycle\ 1-2 cycles 2-4 cycle.; 1;-3 cyclcs
(between the imtant
of application of
voltage to the trip
coil and instant of
final arc extinction)'
7 Theory of arc plasma Emits ions of H2 aroLintl 70% and remining a\ Emits ion\ of N, (80% 1 antl 02 (20'2 1 and ~nctallic Emits IOII\ ol S' (I~)~(III\). Emits metallic vapourfrom
tion~~ation \,ipour\ S" (neutron\). iiccom- the contact material. Since
of gares at acetylene antl rnetallic vapoiir\
high temperature<) panied by clcctrons S' the contacts are essentially
and F- and metallic made of copper alloy,
vapours copper having the lowest
(Conrd)