Traction Systems Bonding and Earthing

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Questions and Answers

What is the purpose of bonding in the context of traction systems?

To provide insulation between different electrical parts

To enhance the signal strength for communication systems

To connect two non-current carrying metallic parts electrically (correct)

To store electrical energy for later use

Which type of bond connects two adjacent rails of a track?

Cross bond (correct)

Earth bond

Impedance-bond

Rail-bond

What is the maximum allowable resistance for an earth electrode in the traction system?

15 Ohm

5 Ohm

1 Ohm

10 Ohm (correct)

Which bond is designed to provide a low impedance path for traction return current?

Impedance-bond Signup and view all the answers

What defines a solidly earthed connection?

Direct connection to an earth electrode without resistive elements Signup and view all the answers

Which type of bond is primarily concerned with connecting consecutive lengths of rails?

Rail-bond Signup and view all the answers

What is the role of the earth wire in the traction system?

To provide a path for returning traction currents to ground Signup and view all the answers

What is the purpose of a structure bond in a traction system?

To connect non-current carrying metallic parts to traction rails Signup and view all the answers

How does the return current flow in a 25 kV a.c. 50 Hz single-phase traction system?

Mostly through the earth with limited flow through the traction rail Signup and view all the answers

Which term describes the bond that facilitates electrical continuity with minimal bends?

Short direct connection Signup and view all the answers

In which section are both rails considered traction rails?

Non-track-circuited sections Signup and view all the answers

What is a welded bond primarily composed of?

Copper conductors with M.S. ferrules Signup and view all the answers

What is the ideal outcome of bonding rails in a traction system?

To enhance the flow of return current from earth to traction rails Signup and view all the answers

What type of track is referred to as wired track?

Track providing 25 kV a.c. 50 Hz single-phase overhead equipment Signup and view all the answers

What aspect distinguishes d.c. traction from a.c. traction in terms of rail bonding?

d.c. traction requires bonding for full current flow through rails Signup and view all the answers

Which area is particularly significant for rail bonding in relation to traction return current?

Around traction sub-station-feeding posts Signup and view all the answers

What is the primary reason for bonding rails in a traction system?

To keep the rail voltage low for safety Signup and view all the answers

Why is the traction rail preferred for earthing over an earthing station with an earth electrode?

It provides better earth connectivity due to its material Signup and view all the answers

In sections equipped with single rail-track circuits, what is the purpose of bonding the traction rail?

To minimize the risk of AC voltage at track relays Signup and view all the answers

What is meant by a 'low resistance path' in track circuited sections?

A path that facilitates efficient return for traction and signaling currents Signup and view all the answers

What role do impedance bonds play in a double rail-track circuit?

They provide a continuous path for traction return current Signup and view all the answers

How should non-current carrying metallic parts of support structures be connected?

By a structure-bond to the nearest traction rail Signup and view all the answers

What special consideration is needed when bonding portal structures?

Only one leg of the portal requires the structure bond Signup and view all the answers

What is the purpose of a cross bond at the location of the structure bond?

To connect the rail to the adjacent traction rail Signup and view all the answers

In double rail-track circuits, both rails are bonded for which main reason?

To distribute return current more evenly Signup and view all the answers

What is a potential downside of relying solely on fish plate joints for low resistance?

They may not provide a consistently low resistance path Signup and view all the answers

What is the requirement for bonding when the length of a track circuited rail does not exceed 350 m?

Cross bonds must be provided at both ends of the track circuited length. Signup and view all the answers

In a double rail-track-circuited section, what must be provided at insulated joints?

An impedance bond. Signup and view all the answers

How frequently should connections to earth be made for the non-track-circuited rail?

At distances not exceeding 100 metres. Signup and view all the answers

What bonding is required commencing opposite to a traction sub-station/feeding post?

Rail-bonds for 1000 metres on either side of the sub-station. Signup and view all the answers

What characterizes a wired track on wooden or concrete sleepers?

There are not more than six metallic sleepers in a maximum length of 350 m. Signup and view all the answers

What material should all types of bonds be made from according to the guidelines?

Mild steel Signup and view all the answers

How far beyond the last traction mast should rail bonds be provided?

50 metres Signup and view all the answers

What is the minimum cross-sectional area for an earth wire used in bonding traction masts?

50 mm2 copper equivalent Signup and view all the answers

How should a rail-bond be connected to the traction rail in a track circuited section?

Longitudinally across the fish plate joint Signup and view all the answers

What type of connection is required for a structure-bond according to the guidelines?

Rigidly connected with galvanized steel fasteners Signup and view all the answers

What should be used if it is not possible to provide a rail-bond?

Welded bond Signup and view all the answers

Where should cross bonds be applied in relation to traction rails in single rail-track-circuited sections?

To adjacent tracks at intervals of not less than 100 m Signup and view all the answers

What must the bond connecting the return conductor to the traction rail be made with?

GI nuts and bolts Signup and view all the answers

For bonding in single rail-track-circuited sections, how far on both sides of the track circuited length should rail bonds exist?

50 m Signup and view all the answers

What type of fasteners should be used for rigid connection of a rail-bond?

Galvanized steel fasteners Signup and view all the answers

What does a 'longitudinal bond' specifically refer to in a traction system?

An electrical connection across a rail joint between consecutive lengths of rails Signup and view all the answers

Which characteristic defines an 'earth electrode' in a traction system?

A metal pipe or plate connected to the general mass of the earth Signup and view all the answers

In what scenario would an 'impedance-bond' be used?

To provide a low impedance path for traction return current Signup and view all the answers

What is the maximum resistance allowable for an earth electrode according to the bonding guidelines?

10 Ohm Signup and view all the answers

What is a 'cross bond' primarily designed for in a traction system?

To link two rails of adjacent tracks Signup and view all the answers

Which of the following best describes a 'solidly earthed' connection?

A connection directly tied to the earth without extra resistance Signup and view all the answers

What is the significance of having a 'rail-bond' in a traction system?

To ensure circuit continuity at rail joint connections Signup and view all the answers

What is the purpose of providing equi-potential links/switches in relation to the siding or secondary loop line?

To maintain a ground potential equal for safety during loading/unloading operations. Signup and view all the answers

How frequently should transverse-bonds be installed between the rails of a siding or secondary loop line?

At distances not exceeding 30 metres apart. Signup and view all the answers

What is the minimum cross-sectional area required for the strips or flats used to connect steel structures of a girder bridge to a traction rail?

200 mm² Signup and view all the answers

Which of the following statements about the bonding of girder bridges is accurate?

A single rail track section must have the traction rail bonded and earthed at both ends of the bridge. Signup and view all the answers

Which bond is primarily responsible for ensuring electrical continuity between the rails where vehicles containing petroleum products are berthed?

Equi-potential bond. Signup and view all the answers

What is the maximum length for a cross bond to be provided in a track circuited rail?

350 m Signup and view all the answers

What is the required distance for connections to earth for non-track-circuited rails?

100 metres Signup and view all the answers

What must be connected to the insulated joints in a double rail-track-circuited section?

An impedance bond Signup and view all the answers

What happens if the length of the earth wire exceeds 1000 metres in a traction system?

It must be made electrically discontinuous Signup and view all the answers

How far should bonding extend from a traction sub-station/feeding post for all traction rails?

1000 metres Signup and view all the answers

What characterizes a track deemed as wired track within the guidelines?

It includes more than six metallic sleepers in any length not exceeding 350 m Signup and view all the answers

What is the minimum cross-sectional area for the mild steel strips used in connecting non-track-circuited rails to earth?

200 mm2 Signup and view all the answers

In a double rail-track-circuited section, what should not be provided between the rails?

Cross bonds Signup and view all the answers

What is the maximum distance allowed between traction masts for sections of the earth wire in a double rail-track-circuited section?

500 m Signup and view all the answers

What is the primary function of the cross bonds placed at specific distances from a traction sub-station?

To maintain electrical continuity Signup and view all the answers

What is the minimum cross-sectional area required for a structure-bond used in traction systems?

200 mm2 Signup and view all the answers

What type of fasteners should be used for connecting a structure-bond to its support?

Galvanised steel fasteners Signup and view all the answers

Which bonding method is used if a rail-bond cannot be provided?

Welded bond Signup and view all the answers

In a single rail-track-circuited section, how far beyond the track circuited length should rail bonds be provided?

50 m Signup and view all the answers

What cross-sectional area should an earth wire used in bonding traction masts have?

50 mm2 copper equivalent Signup and view all the answers

How frequently should traction rails in adjacent tracks be cross bonded?

Every 100 m Signup and view all the answers

What is the primary connection method for a rail-bond in a track circuited section?

Connected with galvanized steel fasteners Signup and view all the answers

What is the main advantage of bonding the traction rail compared to a standard earthing station with an earth electrode?

It offers a lower earth resistance than other methods. Signup and view all the answers

What should be used to connect the return conductor to the traction rail?

GI nuts and bolts Signup and view all the answers

What type of bond should be provided for traction rails in a single rail-track-circuited section?

Both rail bonds and cross bonds Signup and view all the answers

In a double rail-track circuit, what is the purpose of longitudinally bonding both rails?

To ensure even distribution of return current. Signup and view all the answers

What is the required connection for a cross-bond between traction rails?

Rigidly connected by galvanized steel fasteners Signup and view all the answers

When should a structure bond be connected to an earth wire instead of a traction rail?

When traction masts are located away from the track. Signup and view all the answers

What is the role of impedance bonds at insulated joints?

To maintain a continuous path for traction return currents. Signup and view all the answers

How is a cross bond utilized in the context of traction masts located on railway platforms?

To connect the structure bond to adjacent traction rails. Signup and view all the answers

Why is it critical to minimize the ac voltage drop along the length of the traction rail?

To protect sensitive track relays from voltage spikes. Signup and view all the answers

What is a common misconception regarding fish plate joints in rail circuits?

They provide a reliable low resistance path. Signup and view all the answers

What specific bonding requirement is mandated when bonding structures to traction masts?

Only one leg of a portal structure is necessary for bonding. Signup and view all the answers

What aspect related to bonding in a track circuited section is considered essential?

Bonds must extend a specific length beyond track circuits. Signup and view all the answers

Study Notes

Scope

This code applies to 25 kV ac, 50 Hz single-phase traction systems.
It covers bonding and earthing of overhead equipment masts, structures, and associated rails.
Booster transformer stations, switching stations, signaling, and telecommunication equipment are excluded.

Definitions

Bond: Electrical connection between conductors of non-current-carrying metallic parts (traction masts/structures/supports and rails).
Cross bond: Connection between two rails of a track or rails of adjacent tracks (also called transverse bond).
Earth wire: Conductor run on traction masts, structures, or supports connected to the metallic parts and earth.
Earth: Connection to the general mass of earth through an earth electrode. – Earth electrode: A metal plate, pipe, or other electrically connected conductor firmly connected to the general mass of earth.
Impedance-bond: Low impedance path for traction return current, high impedance for track circuit current.
Rail-bond: Electrical connection across a rail joint between consecutive lengths of rail.
Rail length: Continuous rail length, with or without welded joints, no fish plate joints.
Structure bond: Connecting non-current-carrying parts of traction masts, structures or supports to the traction rail.
Signal bond: Electrical connection across a rail joint for track circuit current, provided by the Signaling & Telecommunication Department.
Short direct connection: Electrical continuity connection across a rail joint, as short and direct as possible. – Traction Rail: Non-track-circuited rail in a wired track, not needed for signaling and which may be earthed.
Welded bond: Bond made of standard copper conductors joined with MS ferrules.
Wired track: Track with 25 kV ac, 50 Hz single-phase overhead equipment.

Bonding

For 25 kV ac systems, traction current is drawn from overhead equipment via traction rails; return current mostly flows through earth.
Bonding of rails is essential (unlike DC traction) due to return current spreading and reducing rail voltage.
Bonding of rails is crucial where traction return current passes.

Track circuited sections

Bonding ensures low voltage drop for track relays in single-rail circuits.
In double-rail sections, bonding provides low resistance path for return and signal currents.

Structure bond

Metallic parts of traction masts, structures, supports, concrete/wooden masts connect to nearest traction rail or earth wire.

Track Bonding

In non-wired station yards, rail bond and cross bond are provided for 50 m beyond traction mast.

Mode of Connection for Bonds

Rail bonds, cross bonds, and structure bonds must use mild steel, with a minimum cross-sectional area of 200 mm².
Structure bonds use galvanized steel fasteners.
Rail bonds are connected across fishplate joints in track-circuited sections.
Where rail bonding isn't possible, welded bonds are used.
Connections use Gl nuts, bolts, and spring washers.
Earth wire cross-sectional area isn't less than 50 mm² copper equivalent (in tunnels or double rail-track-circuited sections).

Bonding in single rail-track-circuited sections

Rail bonding continues 50 m beyond track-circuited length; cross-bonding to nearby tracks every 100 m.
For track lengths less than 350 m, cross bonds are provided outside the track length at both ends.

Bonding in Double-rail track-circuited sections

Both rails are bonded, impedance bonds are added at insulated joints.
Earth wires run on masts where no traction rail is available for bonding.
For distances exceeding 1000 m, the earth wire is made electrically discontinuous by using insulators.

Bonding to Traction Substation/Feeding Post

Rail-bonds and cross bonds are provided for 1000 m on either side of the station/feedback post. Specific distances are also provided.

Bonding of Rails on Wooden/Concrete Sleepers

Cross bonding at no more than 350 m intervals when the maximum track length is 350m.

Bonding in Loco sheds and Loco/EMU stabling sidings.

Bonding at 100-m spacing in loco yards, and to adjacent sidings and dead ends.
Rails on wooden/concrete supports in inspection pits are bonded along the whole length and 50 m outwards.

Tunnel Bonding

Bonding extends throughout tunnel and 50 m outwards on each side. Cross bonding is provided between the ends of the tunnel. If tracks are track-circuited use clause 4.0

Bonding of Rails on Weighbridge

Both rails are bonded within 50 m of the weigh bridge. Wooden/concrete-supported rails are connected to earth.

Bonding at Level Crossings

Cross bonding is done within 5m of a level crossing’s edge.

Bonding at Oil Depot Sidings

Double insulated blocks joints if available near turnouts to oil depots.

Bonding of Girder Bridge

Steel bridge structures are connected to traction rails or earth using mild-steel strips.
In single-rail track-circuited section, the non-track-circuited rail is bonded and connected to earth at both ends of the structure .

Bonding of Metallic Parts inside Tunnel

An earth wire is run inside the tunnel, connecting all non-current-carrying parts of overhead equipment support, and is connected to earth and traction rails.

Bonding of Over Line Structures

Metallic parts of foot/road over bridges, over-line structures are connected to a traction rail or an earth using two mild steel strips.

Bonding of Exposed Metallic Parts

Metallic parts not connected to overhead equipment but within 20 m of electrified track (and parallel within 350 m) must be connected to earth or traction rail, but with distances of maximum 350m.

Bonding of Earthing Heel of Isolator Switch

The isolator's earthing heel connects to the supporting traction mast/structure/support with mild steel strips (minimum 200 mm²). The support is then further connected to a traction rail or earth, and an earth.

Connection of Return Conductor

Booster transformer return conductors connect to the midpoint between adjacent stations, or, in double-rail track-circuited sections, to the midpoint of an impedance bond.

Drawings

RDSO issued drawings for bonding practices are listed.

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Description

This quiz covers bonding and earthing principles specific to 25 kV AC, 50 Hz single-phase traction systems. It includes definitions and important components like earth wires, bonds, and earth electrodes essential for understanding the electrical connections in these systems.