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

detected by normal distance protection relay. Hence, a sepreate relay called
Delta I relay is provided for the purpose.
5.9.2 The normal zone of a sub-station to neutral section varies from 25 to 40Km.
Under emergency feed condition, however, the zone would extend upto the next sub-station by
closing the bridging intrruptors at the neutral section and will be about double the zone of
normal feed.It will be apparent from the impedance value given in para-4 that the fault current
under such condition could be well below the traction load current. Over current or plain
impedance relay which operate below a certain impedance level and which function
independently of the phase angle between voltage and current, will be unable to discriminate
of the argument of the impedance of given argument is required.
5.9.3 The protective system shall, therefore,comprise the following relays
i) An admitance(MHo) relay to cover the zone of protection i.e. from the sub-station to
the adjacent sub-station and operate for any earth fault on the overhead equipment
in the zone .In order to allow for the additional impedance of booster transformers
and return conductor, the relay shall have a reach of atleast 125km of single track
OHE with an impedance of 0.52 ohm/km at 70 degree phase angle.
ii) an admittace (MHo) relay for protection against wrong phase coupling due to phase
to phase fault with 120 degree or 60 degree phase difference between two
phases,with a maximum torque angle of 125 degree to 145 degree.The relay may
preferably be provided with a forward offset to prevent it from operating on phase to
earth faults.
iii) An over current relay of instantaneous type which can clear faults between the substation
and the section, with an adjustable current setting ranging from200%to800%.
The instantaneous relays shall of 10 class with operating time not exceeding 10 ms.
iv) A single shot auto reclosing relays to work in conduction with master trip relay shall
be provided.
v) Pantoflash over relay for protection of OHE from flasover caused by movement of
pantograph from live to dead OHE across be insulated overlap provided in front of
traction sub station If Nutral section is provided in front of TSS, then there is no
need of panto flashover relay.
vi) Delta I relay is provided for detection and clearance of high resistance earth fault of
OHE (not detectable by Distance Protection Relay).
5.9.4 The relays (i), (ii), (iii), (v) & (vi) above shall trip the corresponding feeder
circuit breaker in case of fault , through a high speed self reset type tripping relay to be
designated as Master trip relay.
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