Signalling in Electrified Areas

Objectives of Signalling in Electrified Area

• To ensure continuous normal functionality of signalling equipment amidst traction current.
• Prevent interference from traction systems causing false signals or endangering train operations, even under faulty conditions.
• Protect equipment and personnel from electric shock hazards.

Factors Affecting Signalling

• Signal visibility is impacted by Overhead Equipment (OHE) structures.
• Electrical clearances are needed near live OHE.
• Traction return current influences signalling.
• Both Electrostatic and electromagnetic induction affect signaling.

Managing Signal Visibility

• Proper placement of OHE structures during the design phase is crucial for signal visibility.
• If electrical clearances cannot be maintained, protective shields are necessary for signal structures.
• The OHE layout plan should align with an approved Signalling Plan.

Electrostatic and Electromagnetic Induction

• Electrostatic induction is diminished by using underground cables with metal sheaths.
• Electromagnetic induction leads to voltage and current development in conductors near tracks, including rails, cable sheaths, and signalling circuits.
• Voltages create potential gradients and differences along conductors and adjacent grounds.

Factors Influencing Induced Voltage

• Length of parallelism influences the induced voltage.
• Soil conductivity affects induced voltage.
• Also, the Screening efficiency of cable sheaths is a factor.
• The amount of return current through rails and return conductors influence induced voltage.
• Mutual inductance between catenary and cable conductors impacts induced voltage.
• Separation distance between catenary and cable is a factor.
• Furthermore, the current carried by the catenary is also to be considered.

Signal Structures in Electrified Areas

• Color light signals are mandatory.
• Masts, insulators, wires, and supports must not obstruct signal visibility.
• Signals must maintain a minimum clearance from live parts of OHE (Overhead Equipment).
• Actual visibility must be checked by a Signal Sighting Committee.

Broad Gauge Signal Clearance

• Use the signal clearance diagram to determine location and protection.
• Drawing No. 22-D1 is for tangent tracks and tracks with super elevation less than 60 mm.
• Drawing No. 22-D2 is for curved tracks with super elevation from 60 mm to 140 mm.
• Drawing No. 22-D3 is for curved tracks with super elevation from 140 mm to 185 mm.
• Signal posts and fittings cannot infringe into the un-shaded area.
• Signal infringement into the shaded area requires special protective measures as per para 22.2.6.

Diagram Exceptions

• Diagrams 22-D1, 22-D2, 22-D3 dotted outlines are applicable for two sets of catenary/contact wires in insulated and uninsulated overlap locations.
• Diagrams are not for anchor spans, turnouts, within 3 meters of masts, or in loco sheds/inspection pits
• Diagrams are not for feeder lines running with masts or near booster transformers/return conductors.

Contact Heights

• Standard contact wire height is 5.60 meters at supports.
• Catenary's highest point is 7.05 meters.
• In tunnels/under bridges, contact wire can be as low as 4.58 meters with adjustments to catenary height/termination.
• Clearance diagrams accommodate catenary and contact wire positions.

Safety Clearances

• Maintain a minimum of 2 meters from live OHE parts.
• If signal parts are within 2 meters of a 25 kV conductor, then protect it with iron screening connected to the structure.
• If screening is not feasible, install a caution board at 3 meters above the rail level.
• Engineers should always exercise proper working practices
• Maintain awareness of live return conductors.
• A Signal Engineer explains instructions to staff for proper compliance.

Neutral Section Location

• The neutral section should be away from stop signals, level crossings, tangent tracks, and level ground.
• For neutral sections after a stop signal, the distance must allow trains to coast through without stalling.
• For neutral sections before a stop signal, the distance must prevent trains from passing the signal while coasting.
• Preferably the distance should be 1600m away on sections with gradient up to 1 in 300 and 2500m on steeper gradients like 1 in 200.
• Place PTFE short neutral sections at least 400 m after and 200 m before stop signals on level tangent tracks.

Signal Placement

• Signals are typically on the left side.
• Signals can be on the right in special conditions.
• The OHE masts should be placed according to the ACTM for clear visibility.
• If that's not possible, use offset brackets.

Signal Post and Mast Distances

• When a traction mast is in front of a signal post, the distance must be more than 30 meters.
• No traction mast should be less than 10 meters in advance of the signal post.
• Zonal railways' PCSTEs/PCEEs may allow mast placements to be reduced from 30 to 10 meters on straight tracks.
• This occurs after confirming sufficient staggering for signal visibility as per ACTM/SEM.

Height and Structures

• The signal post should be high enough to see clearly.
• On tangent tracks, locate the signal inside the OHE structure, meaning the signal on the track centre must be less than the OHE mast.
• The setting of OHE masts near color signals should comply with para 20.5 of the AC Traction Manual, Vol-II (Part-!I). Annexure:22-A1.
• On curved tracks or obstructed areas, a signal sighting committee must assess the best location.

Restrictions

• Posts or fittings of color signals cannot interfere with track dimensions from the center line.
• OHE masts' distance should follow Drg. No.22-D6.
• Red signal center lines should be at 3.65 meters above rail level.
• Signals lacking route indicators cannot exceed 5.2 meters in height.
• No OHE structures should be within 600 meters behind signals between tracks.
• Portal drop arms need to be at least 600 meters away from signals when between tracks.

Mounting

• If portal drop arms are needed behind a signal, the signal requires mounting on an offset bracket.
• Always perform a study to see whether the drop arm and the signal are offset from track center lines.
• Any study must consider at least three portal drop arms behind the signal.
• Also, shortening of portal drop arms is an acceptable counter measure.
• OHE masts' setting distances should follow Drg.No.22-D7 for junction indicator signals outside tracks.

Other Guidance for Signals with Junction Indicators

• Precautions and parameters of 22.3.4. apply to portal drop arm location.
• Refer to Drg.No.22-D7 for detailed drawings.
• An Official checks signal visibility by day and night post-OHE work (masts, brackets, wiring).
• If visibility is inadequate, the official should impose slower speed restrictions and improve visibility.

Special Cases

• For clearances for High Rise OHE (for Running Double Stack Container & Three Tier Car), refer to Annexure: 22-A3 and Drg.No.22-D7.

Guidelines

• Aerial circuits are prohibited in electrified zones.
• Verify the parallelism length and block wire distance from electrified tracks to ensure the induced voltage has to meet CCITT limits of 60 volt maximum.

Instrument Regulations

• Earth-return circuits are forbidden except for specific block-instrument circuits is A.C. electrified territories.
• All block instruments should be protected by an approved filter, as detailed in Chapter 18 of SEM.

Equipment

• AC-induced voltage can damage electrical signalling equipment.
• The equipment below can only be used inside a cabin, location box, or internal circuits and, should be powered by a separate battery/DC-DC Converter separate from external circuits:
  • Luminous Indicators
  • Telephone type relays
  • Electrical Lever Locks
  • Door Coil of IRS Block Instrument
  • 250 Ohm D.C. neutral Line Relay
  • Rotary Key Transmitter
  • D.C. Neutral Polar Relays

Wiring Standards

• Batteries and wiring must be insulated from ground inside the equipment, location box, or cabin.
• PVC insulated wires that meet specification IRS- S-76 are required for wiring in location boxes and cabins.
• External and internal circuits need their own Batteries/DC-DC Converters.

Cable Management

• When running multiple cables between locations or cabins, wires for individual circuits should be within the same cable.
• Polarized Relays with a permanent magnet can not be used in 25 kV AC electrified areas.
• The magnet loses its magnetic property from induced voltages.
• Any exceptions need competent authority authorization.
• Protective relays used for interlocking must be slow-acting to avoid unintended releases that are caused by minor voltage variations.

Time Delay

• A time delay of 0.6 to 0.8 seconds needs to be designed into circuits.
• External circuits in AC electrified areas must use double cutting.

Limiting Parallelism

• Any signalling line circuit length must be limited to ensure that the traction system’s induced voltage is less than 400 Volts under normal conditions.
• Also, line circuits must be sectionalized, as needed.
• Use sectionlized circuits such as buildings, enclosures, ect, to prevent exceeding induced voltage limits.
• Have specialized power supply units installed for each direction.
• Buried unscreened cable’s induced voltage is rated as 116 Volts/km on a single line and 95 Volts/km on a double line.

Cables Limits

• Immunity needs to be considered when circuits are terminated on relays or equipment.
• Relay immunity must have at least 400V AC.
• The length of the feed cable for relays will need to be reduced to accomodate AC immunity.
• To ensure human safety, safety must be at the forefront with a safety factor of 1.5x, while maintaining a maximum of 400V of permissible induced voltage.

DC Limits

• Direct Current circuits need to use unscreened cable that are using line relays
  • QNA1/QNNA1/QNA1K can have a max length of 2.1 km on a single line and 2.8 km on a double line
  • K50 B1 can have a max length of 1.0 km on a single line and 1.2 km on a double line
  • K50 B1-A2 can have a max length of 2.1 km on a single line and 2.8 km on a double line
  • K50 can have a max length of 750 meters on a single line and 900 meters on a double line.

Immunized Circuits

• AC Immunized circuits can have a max length of 2.1 km on a single line and 2.8 km on a double line.
• These signal feed systems must use 110V 50 Hz type or any approved type.

Signal Control Guidelines

• The separation distance of signal control relays and the signal location in electrified zones must not breech preset limits.
• This ensures minimal voltage gets inducted in the system to illuminate lamps, which also protects under adverse conditions, even under scenarios with major faults.
• When signals are located outside of the limits as stated in section 22.6.3, said signals must be managed through localized relays.
• Transformer circuits must be distinct from transformers to avoid exceeding power feed of primary transformers.

Operating Standards

• Mechanical switches will need special protective measures to be taken with electrical operation having limits on control relays.
• The electric operation of the points must have AC-immunized relays.
• Using approved drawings standards should be the primary basis to which the rods should be insulated.
• Rod connections should always have insulators
• Avoid contact in signal wires where there are rail lines or OHE masts.

Safety

• Where applicable, ensure that parts have ground connected steel that is shielded from solid electrical parts.
• All parts must maintain a standard clearance, or as otherwise directed by the standards for normal movement standards.
• The standards for power arrangements, cables and protection of staff are a high priority to follow and should be adhered to and upkept regularly.
• Proper measures must me in place when there are overhead dangers, which may jeopardize the safety of operations.
• In all scenarios, safety must prevail and any dangers must be avoided above all else.

Maximum Permissible Length for Point Machines:

• As per IRS S-24, a 160V machine gives 910/1100m single/double line, and a 400V machine gives 2200/2800m single/double line.
• The safety factor is 1.5.

Insulated Rod Joints for RE:

• Insulated rod joints follow approved drawings.
• Each rod includes an insulator close to the cabin, preventing contact between insulated and un-insulated parts.
• An insulator is placed between the last adjustable crank and the point or lock bar, preventing rail voltage transfer.
• If the distance between insulators exceeds 300 meters, intermediate insulators are added.
• Each Point, Trap indicator, and lock bar rodded action must be isolated from the track.
• All insulators in a run are positioned between the same two sets of rollers and guides, preventing the insulated portion of one rod from contacting the un-insulated portion of another rod.
• The insulator clearance and the adjoining rod roller must allow normal rod movement.
• The rod top should be at least 40 mm from the rail bottom when crossing the track. Steel or C.I sleepers also need a 40 mm clearance. O.H.E masts and point rods also need 40mm.
• Locally worked points on all electrified lines, as well as points from non-electrified tracks next to the last electrified line, require an insulator to insulate the point lever/box from the rail.
• The engineering department will put in insulators when they're providing a point lever/box for you.

Considerations for Staff on Signal & Telecommunication Equipment in 25 KV A.C Traction Areas

• Suitable precautions are mandatory on electrical equipment and circuits near 25 kV A.C with careful observation of equipment by a signal engineer.
• Workers need to wear rubber gloves and use insulated equipment to protect against shock and induction hazards.
• Any work on or near overhead lines, with the potential of induced voltage, requires full personal protection and grounding, by qualified personnel.
• Precautions are required to avoid direct touch or indirect exposure to the 25 kV conductors.
• When working within proximity to 25kV conductors, the insulated tools must be approved and used.

Management of Return Current in Rail:

• Staff must know the potential impact of return current of the rail.
• Induced voltage is always a consideration in cases of paralleled routes.
• There must be appropriate measure to mitigate a danger that can persist out of damaged equipment.

Precautions

• Reduce circuit length, use rubber gloves or mats, and establish electrical connections before cutting.
• Provide insulated tools, rubber mats, and gloves for those working on circuits or equipment.
• There are approved guidelines for the safe operation.
• The staff needs to know, local and regional procedures for treatment of personal electrical shock injuries, this must be posted centrally.

Breakage procedures

• Communicate with the main train station on cable breaks, or accidents, ensure an understanding of the processes, with steps detailed with what to do.
• The train control in the area, in the event of an emergency must stop the traffic nearby from accident or potential equipment damage.
• In accordance to standard operating policy, the staff must conduct visual inspections of all wiring to ensure safe equipment operation.

2.2 kV Charging as an Anti-Theft Measure

• The principal engineer in Telecom and Signal departments are in charge to sign off that electrical hazards.

Masts near Signals

• All workers must know local/regional guidelines for operation of electrical equipment near electrical hazards.
• Review the appendix, for a high level consideration for personnel near dangerous hazards and in a dangerous operation or environment.