Electric Point Machine| Basics of Railway Signalling
An electric point machine is an electrically driven machine used for operation of points in railway yards, and comprises an electric motor, point mechanism, crank handle mechanism. point detector and, a point locking device also.
Electric Point Machine operation
The point machine shall operate in the following sequence: -
(a) Open the detection contacts.
(b) Unlock the points,
(c) Move the points
(d) Lock the points.
(e) Close the detection contacts.
General Requirements of Electric Point Machine Non-Trailable Type (IRS: S 24-2002)
1. The machine shall be of robust construction, securely fixed and protected from Unauthorized interference.
2. The machine shall be so designed that it can be stopped, reversed or obstructed at any point during operation without any damage.
3. The machine shall be so constructed that no movement of the mechanism shall result from vibration or external force applied to the mechanical connection.
4. The machine shall be suitable for either right-hand or left-hand mounting, and shall be so constructed that it can readily be converted at site from right-hand to left-hand
mounting and vice-versa
5. The motor cut-off contacts shall be housed in the mechanism case and so designed that they follow the movement of the mechanism and do not complete their operation until the locking mechanism has completed its function.
6. The locking of the points shall be achieved by means of a locking segment engaging in the locking slot of the lock slide.
7. The locking segment and the notch in the lock slide shall be of substantial size shall have substantial bearing surface between them in the locked position.
8. The entrance edges of the locking slot in the lock slide and the end face of the locking segments shall have square edges. Notches shall be cut to correct size and locking segments shall be made of hardened steel.
9. The detector unit shall have sufficient number of contacts for proving the full normal and reverse positions of the detector slides and the corresponding locked position of the lock slide. It shall also prove the complete operation of the point machine and the complete movement of locking process.
10. Detection and motor cut-off contacts shall be housed in a transparent cover made of UV stabilized polycarbonate material. The sealing arrangement should be provided on the transparent cover and it should be dust proof and water proof. The position of the detection and motor cut off contacts shall be such as to avoid dropping of grease, oil during maintenance work.
11 Electrical contacts shall be of low resistance, quick acting, self-aligning and wiping type and shall conform to IRS: S 23.
12. Provision shall be made for proper and convenient lubrication of the moving parts of the machine, wherever necessary.
13. Exposed oil holes, cups and grease nipples shall be provided with weather-proof spring loaded covers.
14. The design shall be such as to minimize condensation in the machine.
15. Clearance of not less than 12 mm shall be provided between any exposed current carrying parts and other metallic parts insulated therefrom.
16. With the exception of motor commutator, a surface leakage distance of not less than 6 mm shall be provided between any exposed current carrying parts and other metallic parts insulated there from.
17. The insulating materials used shall conform to IRS: S 23 and shall not be injuriously affected by atmospheric conditions.
18. Dimensions of fixing arrangement of point machine shall be as per drawing No. RDSO / S 10800 for 143 mm stroke and RDSO / S 11000 for 220 mm stroke IRS point machine.
Operating Characteristics of Electric Point Machine Non-Trailable type
1. The machine shall comply with the appropriate operating data given in of this specification.
2. The machine shall be capable of operating between the limits of 75 percent and 125 percent of the rated voltage at 450 kg. test load for 143 mm. throw point machine and at 550 kg. test load for 220 mm throw point machine.
3. The machine in locked position, shall be capable of withstanding a thrust of 9000 Kg. through the connections, so that in the event of trail through, the damage is confined to the connections between the machine and points.
4. The friction clutch of the machine shall be factory adjusted to slip at not exceeding 580 kg. load on throw bar for 143 mm throw point machine and at not exceeding 700 kg. load for 220 mm throw point machine. The clutch adjustment shall be sealed in the factory. The slipping load and slipping current shall be indicated on the name plate.
5. The point machine shall have a min. AC immunity level of 160 V (r.m.s.), 50 Hz
Operating Requirements Motor for Electric Point Machine
(IRS: S 37-2022 Version 2.0 )
1. The Motor when connected to an Electric Point Machine shall be capable of complying with the Operating Requirements given in IRS: S 24. It shall also be apable of operating the Point Machine as per IRS: S 24 between the limits of 75% and 125% of the rated voltage
2. The motor shall be capable of functioning normally even after remaining in submerged condition for 24 hours in case of IP-67 Compliant Point Motor.
3. Considering the conditions of the water logging rail tracks in the season of monsoon, Indian Railway introduced watertight motor .
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