remote control equipment - Indian Railways Institute of Electrical ...

vii) Rated short circuit 31.5 kA 20 kA
breaking current
viii) Rated breaking capacity
(Symmetrical)
a) Two Pole 7717.5 MVA 450 MVA
b) Three pole 13366.7 MVA
ix) Rated making current 78.8 kA 50 kA
x) Rated operating sequence 0-0.3 sec 0-0.3 sec
83
CO-3 sec. - CO 30 sec -CO
xi) Total breaking time Not more than 80 ms. Not more than 65 ms
xii) Rated short time 31.5 kA for 20 kA for
withstand current one second 3 seconds
4.5 25 KV INTERRUPTORS
4.5.1 The interruptors ar non-automatic circuit breakers which are provided at feeding
posts and switching stations. Inter rupters ar not required to clear the fault, except for the
one which is provided at the sectioning post as bridging interruptor. This interruptor is called
upon to clear the fault under extended feed conditions. The breaking capacity of the
interruptor has been specified as 4000 Amps at a recovery voltage of 27.5 kV and a short
time current with stand capacity of 4000 Amps. for 3 seconds. But now with the use of
higher rating traction transformers, the breaking capacity and normal rated current has been
incrased to 8 kA and 800 Amps respectively in the RDSO’s new specification.
4.6 ISOLATING SWITCHES
4.6.1 When carrying, out inspection or repair on sub-station equipments, it is
essential to disconnect reliably the unit or the section, on which the work is to be done,
from all other live parts on the installation in order to ensure complete safety of the working staff
to guard against mistakes, it is desirable that this should be done by an apparatus which
makes a visible break in the circuit. Such an apparatus is called the isolating switch or isolator.
Isolators are used to open or close the circuit either when negligible current is flowing or when
no current is flowing through the circuit. These are also called as off load switches. The location
of the isolating switch is decided in the sub-station on the basis of scheme of bus bar
connections. Generally on either side of the circuit breakers, isolators are provided for
attending to maintenance work etc.
4.6.2 Two types of isolating switches have been used in traction substation. On the
primary side i.e. HV side. Isolators used are either of two pole or three pole according to
number of poles. From constructional point of view these may be divided as.