Railway Signalling Electrical Point Machine

Railway Signalling Electrical Point Machine

What is a Railway Electrical Point Machine?

– An electrical point machine is an electrically driven motor used for the operation of points in railway yards. The rotary motion of the motor is transmitted through the reduction gears and transmission assembly and converted through the linear movement of a toothed rack through a pinion. The gear rack drives switch rails to unlock, changes the position from N to R or R to N, and locks the switch at the end of the stroke.

What is the sequence of point machine operation?

1. Opening of the detection contacts.
2. Unlock the points.

3. Move the points to the desired position
4. Lock the points.
5. Close the detection contacts.

 

Depending upon the operating voltages

1. Low voltage.DC supplies – 24 volts DC.
2. High voltage DC supplies -110V DC.
3. High voltage AC – 380 AC.

The point machines have split series field windings.

 

Electrical parameters of point machine

1. Rated voltage – 110V DC.
2. Working current – 4-6 Amps.
3. Obstruction (slipping current) – 6-7 Amps.

4. Operating Time – 3 sec.
5. Type of machine – Combined type. (Operation, locking, and detection)
6. Field winding – Split field

7. Field connection – Series
8. Movement of locking – Rotary type
9. Friction clutch – Self-adjustable

 

Main parts of point machine

1. DC series split field motor within built-in reduction gear unit
2. Transmission assembly
3. Throw rod, lock slides, and detection slides

4. Detection and control contact switch assembly
5. Hand crank.
6. Spring-loaded friction clutch.

 

Need for remote control of point machine:

1. To avoid voltage drop in cable cross-section.
2. Contact of lever /knob/push button does not have the heavy-duty current carrying capacity.

3. Track locking is to be provided to prevent point operation under wheels.
4. Point machine should be protected from overload.
5. Facility for sequential operation should be provided.

 

 

Two types of relay control units are standardized.

1. Siemens point contactor unit.
2. Point contactor unit with QBCA relays.

Visit here for more information:–  https://en.wikipedia.org/wiki/Point_machine

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