Page 690 - Industrial Power Engineering and Applications Handbook

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dri\e\ thc arc i\ ;I\ 2A and even la\.
produced by the lherelore, except
interi-upting cui-rent interrupting current,
itself, and will vary lower than this. these
with the current. interrupters are suitablc
and so will vary to interrupt huch currents
the cooling gas in without current chopping
direct proportion.
The smaller the
current to be
interrupted, the
smaller will be the
magnetic field and
the cooling force,
enabling the arc to
inrerrupt at a
natural current zero
only. But this
technique is now
seldom practised
(iiij Thermal blast and arc
assistance type:
As (i) ahove
9 Application switching (a) Suitable for all
of applications. not (a) Suitable for all Extensively used for all Generally witable for Suitable for all Suitable for all types of
Induction motors requiring frequent applications not LT applications and HT distribution only, applications. Switching of industrial needs and
Generators switching operations. requiring frequent suitable for frequent and at installations capacitor banks, however, lrequent opcration. Their
Transformers (b) Until now they were switching operations operations employing a number of may pose problem ability for quick
Reactors being extensively used for such devices to make because of high TKVs. interruption and fast
Inductive circuits a11 LT applications dry compressed air These may cause a restrike building up of dielectric
Capacitor banks system handy and of the arc plasma and give strength made them
Distribution lines economical rise to switching surges suitable for onerous
Higher-speed auto- duties and high TRVs
reclosing
IO Whether a rurge No No RV Better to provide Ciencrally not Ye\. particularly for dry
arrester is essential (depending upon the insulated equipment (such
type of equipment it is as an induction motor, a
\witching. the minimum dry type reactor or a dry
current it has to interrupt type transformer), which
and the likely amplitude have low insulation le~~els .
of TRV) An oil-immersed equip-
ment (such as a power
tranrformerj. having a
relativcly much bettci-
dielectric strength, may be
\witched without an
ai-rester
(C,Jll/d)