Railway Engineering: Thick Web Switches

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Questions and Answers

What steps should be taken after discovering a blown fuse in a circuit?

Replace the fuse immediately without checking the circuit.

Measure the circuit current and compare it with the original recorded value. (correct)

Ignore the issue if the fuse type is correct.

Only check the wiring for faults.

What is the prescribed fuse rating for LED signal aspects if not specified otherwise?

0.6 Ampere (correct)

0.4 Ampere

0.2 Ampere

1 Ampere

What should happen when the main fuse blows in an auto changeover system?

The system should stop functioning until maintenance is performed.

A visual indication should not be provided.

The system should automatically switch to a spare fuse. (correct)

Overload protection should be disabled temporarily.

Which of the following is NOT part of the groups for checking and testing signalling installations?

Electrical load balancing. Signup and view all the answers

Which measures can be implemented to prevent failures due to blown fuses?

Implementing an auto changeover system with alarms. Signup and view all the answers

What is the main responsibility of the Engineering Department regarding the Spring Setting Device (SSD)?

Installation and maintenance Signup and view all the answers

Where is the Spring Setting Device (SSD) specifically placed?

Between sleeper number 13 and 14 Signup and view all the answers

What is the purpose of checking the detection contacts after they are closed?

To confirm they flex slightly Signup and view all the answers

Which of the following is NOT an observation required during the Obstruction Test?

The point is locked by the clamp lock Signup and view all the answers

Which factor is indicated for checking the electrical detector's adjustment?

An obstruction of 3.25 mm thickness at a distance of 150 mm Signup and view all the answers

What is required for the nuts used in the installation process?

They must be equipped with a spring washer Signup and view all the answers

Which component must be insulated from the ground connection according to the Insulation Test?

All of the above Signup and view all the answers

What is the minimum capacity for fuses provided in signalling installations?

No less than 2.5 times the rated current Signup and view all the answers

What should be adjusted to ensure that shunt contacts do not make before the detector contacts break?

Shunt contacts adjustment Signup and view all the answers

What information should be recorded during the commissioning of signalling installations?

The normal load current of every circuit Signup and view all the answers

When installing Electrical Point Detectors (EPD), what area is specified for mounting them?

Beside the close switch leading to high-speed movement Signup and view all the answers

Which of the following must be observed for the Lock Segment during testing?

It must not enter into the notches of locking slides Signup and view all the answers

How should the location of switch and lock slides be maintained?

By using locating marks on the slides Signup and view all the answers

In case of circuit controllers, what is the normal practice regarding new installations?

They are not newly installed except in specific cases Signup and view all the answers

In what condition should the detectors be mounted according to the guidelines?

Clear of all infringements as per approved plan Signup and view all the answers

What additional measure may be taken if a fuse does not have a blown-off indication?

Install an additional indication circuit Signup and view all the answers

What is a primary deficiency of conventional over-riding type switches?

Weakness of the tongue rail due to machining Signup and view all the answers

How wide is the switch opening of Thick Web Switches compared to conventional switches?

160 mm Signup and view all the answers

What type of point machine is used for the operation of Thick Web Switches?

Electric point machine of approved type Signup and view all the answers

What happens during the first 60 mm throw of the point machine for Thick Web Switches?

Closed switch rail gets unlocked Signup and view all the answers

What is the result of having no stretcher bar in Thick Web Switches?

Both tongue rails move independently Signup and view all the answers

What adverse effect is experienced by vehicles due to conventional over-riding switches?

Jerk from obstruction at the switch toe Signup and view all the answers

What ensures direct locking between the tongue rail and stock rail in Thick Web Switches?

Proper ground connection and clamp lock Signup and view all the answers

What is one major advantage of using Thick Web Switches over conventional types?

Improved lateral force resistance at higher speeds Signup and view all the answers

Study Notes

Section 4: Thick Web Switches (TWS)

Conventional switches suffer from geometrical deficiencies like weak tongue rails susceptible to heavy wear, obstructions to wheel flanges, and twist in the track.
Thick Web Switches (TWS) are non-overriding and overcome these problems with wider switch openings (160mm vs 115mm).
Ground connection and clamp lock are used for operation.
Approved electric point machines with specific throws (e.g., 220mm) are used for operation and clamp locking.
Open and closed switch rails move independently, offering direct locking for both positions. A stretcher bar isn't used.

Section 19.4.4 Spring Setting Device (SSD)

SSDs are provided at rail junctions to assist proper switch setting.
Placed between sleepers 13 and 14.
Insulated from both rails.
Installation and maintenance are the responsibility of the Engineering Department.
Ground connection and clamp locks for thick web switches are installed according to RDSO drawings.

Section 19.4.6 Obstruction Test

Detector slides, lock slides, and drive rods must be adjusted, with a 5mm thick test piece placed between the switch and gauge face of a stock rail 150mm from the toe of the point.
Observations must include friction clutch disengagement, the point not locking, the lock segment not entering notches, switch detection contacts not making, and no exceeding twice normal working current, during the test.

Section 19.4.7 Insulation Test

Check that point machines are insulated from ground connections.
Spring setting devices and clamp lock assemblies must be insulated from both rails.

Section 5: Installation of Electrical Point Detector (EPD)

Approved EPDs are installed beside switches leading to high-speed movements, clear of obstructions.
Mounted on the left or right-hand side of the point layout.
Contacts adjusted to make/break simultaneously. Shunt contacts need to be adjusted so they don't make before the main contacts break (on AC traction).
Tightened nuts and screws are required, particularly spring washers.
Slides are checked for free movement before connections are made.
Locating marks on switches and lock slides are used for correct positioning.
Circuit Controllers (e.g. LC Gates) may be phased in for some locations.

Section 6: Signalling Relays

Information on signalling relays can be found in Annexure 21-A1.
Covers general requirements, installation procedures, sealing, maintenance, periodical inspections, and replacement. (refer to section numbers for specifics).

Section 7: Fuses

Approved fuses with appropriate ratings are required.
Normal load current is recorded during commissioning, these recorded values check against theoretically calculated values.
Fuses should be at least 2.5 times the rated current.
When a fuse blows, measure and compare the current with the original recorded value, fix the defect before replacing the fuse.
LED signals require 0.6 Ampere fuses (unless otherwise specified).
Auto Changeover System is an option that monitors and alerts on blown fuses. System changes circuits automatically to a backup fuse using audio/visual signals. The system can be designed for 24V DC, 60V DC, or 110VAC.

Section 8: Testing of Signalling Circuits

Signalling installations are divided into physical inspection, wiring & cable checks, individual circuit testing, individual apparatus testing, and overall system testing.

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Description

Explore the intricacies of Thick Web Switches (TWS) and Spring Setting Devices (SSD) in railway engineering. This quiz covers their operational mechanisms, advantages, and installation protocols. Test your knowledge on non-overriding switches and the role of SSDs in ensuring optimal switch settings.