2. 25 kV AC Traction Safety Requirements
• Major Track Maintenance Works:
An authorised OHE staff should invariably be present, when
relaying work or any major work on track is carried out, in
order to ensure the following points:
(i) Power block is correctly taken and permit to work is issued;
(ii) The structure bonds, track bonds, cross bonds, longitudinal
rail bonds etc. are not disturbed and if disconnected for the
work, they are reconnected properly when the work is
completed.
(iii) The return feeder connections to the rails at the feeding
posts are proper and not disturbed.
(iv) The setting distance of the structure do not affected during
slewing.
3. 25 kV AC Traction Safety Requirements
• Major Track Maintenance Works:
(v) The track level is not raised beyond the permissible limits
during the work;
(vi) Excavation or digging near a mast foundation is done in such a
manner that the foundation is not exposed;
(vii) The clearance particularly at over line structure is maintained
to the required standards; (viii) Precautions for the safety of staff
working under the OHE are taken correctly.
(viii)The Engineering officials in charge of such major work shall
ensure that intimation to their counterparts for OHE maintenance
work is given with adequate notice.
4. 25 kV AC Traction Safety Requirements
• Major Track Maintenance Works:
(ix)Voltages are induced in conductive lines, rails and fence
running parallel to the traction lines. With the use of underground
cables and OFC the induced voltage/interference problem in the
communication circuits is practically resolved.
(x)The value of induced voltage depends on various factors such as
length of parallelism between the cable and electrified track, soil
conductivity, screening efficiency of cable sheath, return current,
through the rails and return conductor where provided, mutual
inductance between catenary and cable conductors, current carried
by the OHE.
5. Major Track Maintenance Works:
(xi) Appropriate precautions to overcome the effects of the
induced voltage, therefore, have to be taken by S&T department.
(xii) Other aspects where S&T equipment is affected are:
i) OHE masts and fittings may come in the way of visibility of
signals to some extent and may come in the way of signal.
ii) Restrictions in the path of traction currents on section provided
with track circuits.
25 kV AC Traction Safety Requirements
6. 25 kV AC Traction Protection
• The protection of 25 kV ac traction equipment is achieved by
using different types of protection relays provided at the
Traction Substations.
• The protection relays protect traction equipment like
transformers, OHE, Capacitor banks etc. in case of faults
(short circuits).
• Maximum no. of faults occur on the OHE because of its wide
spread geometry and maximum exposure to external objects
(birds, monkeys, snakes, clothes, kites, pollution and weather
conditions etc.).
7. 25 kV AC Traction Protection
• In order to avoid disruption of traction supply to OHE in case
of transient faults an auto recloser arrangement is adopted
which automatically closes CB after 500 ms.
• Only in case of permanent faults on OHE relays trip the CB
again and then TPC has to identify the faulty subsector by a
well defined logic and finally segregate it using SCADA
system.
• The relay status are also monitored by SCADA system.
8. 25 kV AC Traction Protection
• Reliable, high speed and accurate protection systems
are required.
• Diverse range of rolling stocks(rectifier based to 3-
phase drives having regenerative braking features)
and poor traction power quality at TSS.
• Safe working depends on properly designed
protection system.
9. GENERAL SAFETY OHE
No work shall be done above or within a distance of 2 meters
from the live OHE without a ‘‘Permit to work’’.
Inductive effects occur on large metallic structural steel of
platforms running parallel to the track. They will gave to be
earthed suitably to afford safety.
Whenever there is a doubt in description , the person asking
for power block shall state clearly the track and OHE structure
numbers between which work is to be done.
10. When anybody deputed to RRI/Stations for taking power
block is not sure about switching alternations, movements of
trains during power block mainly in yards he should clearly
tell their JE/SSE that I have confusion regarding the same so
that the accidents can be avoided. It is important that staff who
ask for power block should know the correct method of
identifying and describing any section of OHE where
shutdown is required.
The permit-to-work shall be obtained prior to commencing
work to make sure that power supply has been switched off.
GENERAL SAFETY OHE
11. All message relating to shutdown and restoration of power
supply, permit to work etc. issued over the telephone shall
invariably be supported by exchange of private numbers and
repeated twice.
Men should be posted on both sides of the site of work to warn
the working party of any approaching train on the same track
and adjacent track(s)
Isolator shall not be opened when current is passing through it.
Isolator switches on the main line may only be opened
provided the corresponding sub-sector is first made dead by
TPC.
GENERAL SAFETY OHE
12. For providing earth on the OHE, fix the earthing clamp
securely to a mast at least one span away after making sure
that the mast to earth rail bond of this mast is intact.
Earthing clamp should always be fixed to the traction rail first
and then the top clamp should be hooked to the OHE to be
earthed after touching to RT.
For removing the earthing , first remove the hook on the OHE
and then clamp fixed to the rail or mast.
Each working party shall be protected by at least two
independent earths, one on each side of a working party.
GENERAL SAFETY OHE
13. If the distance between the working parties exceeds 1000
meters, intermediate earths shall be provided in such a manner
as to ensure that the distance between earths does not exceeds
1000 meters.
All staff should wear helmets to protect their heads againsts
aginst any tool or equipment which may drop down accidently.
Staff should protect themselves against an inadvertent fall by
wearing a safety belt for supporting themselves by a rope
sling.
GENERAL SAFETY OHE
14. Ropes used with ladders should be cotton or jute. A ladder should
be held by one person on the ground to prevent slipping, while
the top end should be tied to the supporting structure or
conductor to keep it in position and prevent it sliding away.
Ladder should never be allowed to fall on or rest against the
contact wire.
More than one person shall not normally be allowed on a ladder
as far as possible.
GENERAL SAFETY OHE
15. Climbing on a ladder with wet or slipery foot wear is forbidden.
A rope should be used to pass tools or any equipment to the men
working on a ladder.
No one should stand directly below a work spot under a ladder.
Do not tie the rope on rail without taking traffic block.
Two sections of conductors or ends of conductors which may
have snapped should be separately earthed at two points after
switching off supply to both parts of OHE. This precaution
should also be observed when working in the vicinity of a
sectioning point and cut-in-insulators.
GENERAL SAFETY OHE
16. In electrified tracks ,steel tape or metallic tape or tape with
woven metal reinforcement should not be used.
Ropes, come along clamps, tirfor, pull lifts should be tested once
in a month.
The continuity of the cable connection between the top clamp
and the earthling clamp should be checked once a fortnight.
Cable should be renewed if more than 20% strands are broken.
During use, cable should be continually examined for fraying and
breakage of strands.
GENERAL SAFETY OHE
17. Neutral section should be treated as live equipment and
earthed separately at two points on either side of the work
party before commencing work.
When work is to be carried out on isolator , both sides of
the isolator should be earthed at two points.
No fallen wires should be touched unless power has been
switced off and the wires suitably earthed.
GENERAL SAFETY OHE
18.
19. The attention of all railway staff is drawn to the fact
that under 25 kV ac 50 Hz single phase traction, there
is heavy induction on all metallic structures and
conductors in the vicinity of the track.
The induction is two-fold:
a) Electro-static, which results from the high
potential of 25 kV on the OHE system.
