Chapter 22: Requirements of Signalling in 25 KV AC Electrified Area PDF

Chapter 22: Requirements of Signalling in 25 KV AC Electrified Area Section 1: General 22.1.1 Objectives (a) To ensure that signalling equipment continues to function normally in the presence of traction current....

Chapter 22: Requirements of Signalling in 25 KV AC Electrified Area Section 1: General 22.1.1 Objectives (a) To ensure that signalling equipment continues to function normally in the presence of traction current. (b) To ensure that interference from the traction system cannot, under any circumstances, cause the Signalling system to exhibit false indications, or in any other way imperil the safe operation of trains. This objective must be achieved even if the traction or Signalling system is in a faulty or anomalous condition. (c) To safeguard equipment and staff from electric shock. 22.1.2 Factors Affecting Signalling in AC Electrified Area (a) Visibility of signals due to OHE structure. (b) Electrical clearances of signals due to live OHE close by. (c) Traction return current. (d) Electrostatic induction and Electro-magnetic Induction. 22.1.3 Visibility of Signals shall be taken care of by the proper implantation of OHE structures during the design stage of OHE. Where electrical clearances are not possible to maintain, suitable protective shields for signal structures shall be provided. Lay Out Plan for OHE shall be based on approved Signalling Plan. Note: (i) Protective wire-mesh screen of approved design and size shall be provided wherever clearance of more than 2 meter for any part of the signal from live OHE conductor is not possible to get. (ii) OHE bonds (Structural, longitudinal and cross bonds) to be provided by electrical department in the yard and in the block section wherever required for proper functioning of field S&T equipment. These bonds should be properly fastened with the structure/mast/rails and must be insulated for portion passing under positive rail of track circuit. 22.1.4 The electrostatic induction is practically eliminated by transferring a circuit into underground cables protected by a metal sheath. The Electro-magnetic Induction causes various currents and voltages to develop in conductors parallel to the track. These include the rails, traction return conductors where provided, cable sheath, any other conductors in the vicinity, and signalling and telecommunication circuits. The voltages that occur in the conductors appear as potential gradients. In addition, there are potential differences between various points along the conductors and the adjacent Earths. The value of this induced voltage depends on various factors, such as- Chapter 22: Requirements Of Signalling In 25 KV AC Electrified Area Page 474 of 530  (a) Length of parallelism between the cable conductors and the electrified track. (b) Soil conductivity. (c) Screening efficiency of the cable sheath where existing. (d) Return current through the rails and return conductor where provided. (e) Mutual inductance between catenary and the cable conductors. (f) Separation between catenary and cable. (g) Current carried by the catenary etc. Section 2: Signal Structures in RE area 22.2.1 Colour light signals only shall be used in electrified areas. 22.2.2 On electrified sections, the masts, insulators, wires and supports obstruct the visibility of Signals. In addition, the Signals have to be so erected that they maintain a minimum clearance from the live parts of the O.H.E. The instructions in this section shall be strictly followed in so far as the electrical clearance is concerned. These instructions may be taken as a rough guide in determining the location of signals, which would afford the best visibility to the Loco Pilots of approaching trains. However, the actual visibility shall in all cases, be checked by a Signal Sighting Committee and action to improve the visibility taken on the recommendations of the Committee. 22.2.3 The location of signals and the protection required shall be worked out from the following signal clearance diagram for Broad gauge. Drg. No 22-D1 For Tangent tracks & tracks with super elevation less than 60 mm. Drg. No 22-D2 For Curved tracks with super elevation 60 mm to 140 mm. Drg. No 22-D3 For Curved tracks with super elevation 140 mm to 185 mm. 22.2.4 In these diagrams the un-shaded portion shown above the standard moving dimensions is the area into which a signal posts or any of its fittings shall, under no circumstances, be allowed to infringe. The shaded envelope around this is the area into which a signal or its fittings shall not normally be allowed to infringe. If due to unavoidable reasons, a portion of the signal post or its fittings has to infringe into this shaded area, special protective measures as detailed in para 22.2.6 shall be taken. The dotted outline in Drg. Nos. 22-D1, 22-D2, 22-D3 for Broad Gauge is applicable when there are two sets of Catenary and Contact wires parallel to each other in the same span, viz. insulated and un- insulated overlap locations. It is to be noted that these diagrams are not applicable to (i) anchor spans, (ii) turnouts, (iii) 3 meters on either side of masts, and (iv) in loco sheds and inspection pits. The diagrams are also not applicable when there is a feeder line running along with masts or where booster transformers and return conductors are provided. Chapter 22: Requirements Of Signalling In 25 KV AC Electrified Area Page 475 of 530 22.2.5 The normal height of the contact wire is 5.60 meters at supports. The normal height of the catenary at its highest point is 7.05 meters. In tunnels as well as underneath bridges, where clearances are limited, the contact wire may be as low as 4.58 meters for Broad Gauge and the catenary is also lowered suitably or terminated at the face of Bridges or Tunnels. The clearance diagrams have, however, been drawn to suit the extreme positions of the catenary and the contact wire. In addition, the diagrams make allowances for the stagger as well as displacement of wires by wind. 22.2.6 Clearances for Safety In the matter of electrical clearances, the fundamental rule to be observed is that no one is allowed, under normal conditions, to approach closer than 2 meters from the extreme positions of the live parts of the O.H.E. The following protective measures shall, therefore, be adopted. (a) If any portion of a signal post or its fittings where signalling staff have to work, falls within 2 meters of a 25 KV live conductor, or any metal part electrically connected to this conductor such portion shall as far as practicable be protected by an iron screening of approved design solidly connected to the structural work. (b) If for any reason it is not practicable to provide the protective iron screening as mentioned above, a Caution Board of approved design shall be provided on the signal post at a height of 3 meters above the rail level, to caution the signal staff. Note: Technical personnel shall exercise particular care to protect themselves while working on signal posts not provided with protective screens. If there is any likelihood of any part of their tools or equipment coming within 2 meter of live equipment, they shall take a power block as detailed in Chapter VI of the Manual of AC Traction-Volume II (Part-I). The same precautions are also required in the vicinity of return conductors, which should be treated as live. (c) The SSE/JE (Signal) shall explain these instructions to the staff working under them and ensure that they are correctly complied with. 22.2.7 Drg. Nos. 22-D4 and 22-D5 illustrate the location of signals on the left-hand side and right hand side of Broad Gauge track and the figures indicate the minimum heights and distances of Signal from the track to avoid electrical infringements. Chapter 22: Requirements Of Signalling In 25 KV AC Electrified Area Page 476 of 530 22.2.8 Location of Neutral Section (Reference: Para No. 16.4 to 16.5 of ACTM, Appendix I) Para Neutral section shall be located away from stop signals, level crossing and No. 16.4 shall be on tangent track and on level to the possible extent. Para If neutral section is provided after a stop signal, the distance* between signal and No. neutral section shall be such that after stopping, the train shall be able to pick up 16.4.1 enough speed to coast the neutral section without any risk of stalling. Para If neutral section is provided before a stop signal, the distance* between No. neutral section and signal shall be such that the train shall not cross the 16.4.2 signal in an effort to coast the neutral section. *Note: The distance should be preferably 1600 meter away on section with gradient up to 1 in 300 and 2500 meter with higher steeper gradient up to 1 in 200, if unavoidable. The PTFE type short neutral section shall be located on level tangent track at least 400 m after the stop signal and 200 m before the stop signal. Where, however, modifications require to comply with these guide lines are difficult or entail heavy investment, the Chief Electrical Engineer of the Railway may direct any other arrangement to be followed consistent with safety and reliability, and for location on graded section according to para 16.4.1 and 16.4.2. (Para No. 16.4.5 of ACTM). Section 3: Erection of Signals in RE Area 22.3.1 Location of Signals in RE Area Normally, all signals should be located on the left side of the track for which it refers. In exceptional cases the signals may be located on the right side. To ensure adequate visibility of signals the OHE masts should be implanted as per the ACTM. In case it is not possible, offset brackets may be used for signal units without affecting the schedule of dimensions. Further the following steps should be taken to achieve adequate visibility. (a) In case the traction mast is located in front of the signal post, the distance between the traction mast and signal post should not be less than 30 meters. In addition, it should be ensured that no traction mast is located in advance of the signal post at a distance less than 10 meters. (b) PCSTEs and PCEEs of the zonal railways shall give dispensation for reduction in the distance of placing mast in front of the signal from 30 meters to 10 meters on straight track after ensuring staggering for proper visibility of signal as per provisions of ACTM and SEM. (c) The signal post should be sufficiently high so as to be seen clearly. (d) On tangent tracks it is desirable that the signal should be located within the OHE structure, i.e. the implantation of the signal from the track centre shall be less than the implantation of the OHE mast from the track centre. The setting of OHE masts in the vicinity of the colour light signals shall be as per para 20.5 of Appendix-I of the AC Traction Manual, Vol-II (Part-!I). Relevant extracts as in Annexure:22-A1. Chapter 22: Requirements Of Signalling In 25 KV AC Electrified Area Page 477 of 530  (e) On curved track or in areas, where other obstructions such as buildings, trees etc. exist, the site should be individually examined by the 'signal sighting committee' for deciding the most appropriate location of the signal. 22.3.2 No portion of a post or fittings of a colour light signal shall infringe with the schedule of dimensions from the centre line of the nearest track. 22.3.3 Signals without Junction Indicators Outside Tracks (a) Distance of OHE masts shall be in accordance with Drg. No.22-D6. (b) The signal units shall be so fixed that the height of the centre line of the red signal shall be approximately 3.65 meters above rail level. No part of Signal without a route indicator shall normally be higher than 5.2 meters above rail level. 22.3.4 Signals without Junction Indicators between Tracks (a) If signals are located between tracks no OHE structures shall be provided in the same track space for at least 600 meters in rear of the signals. (b) Portal drop arms shall not normally be located at least for a distance of 600 meters before the signal in track space where signals are located. (c) If a portal drop arm has to be unavoidably located in rear of signal itself, the signal shall be mounted on an offset bracket. In addition special study shall be made in each case to see whether the portal drop arm should also be offset from the centre line of the track space in the direction opposite to the offset of the signal. This special study shall be made for at least three portal drop arms in rear of the signal and shall also cover the possibility of shortening the portal drop arm. 22.3.5 Signals with Junction Indicators Outside Tracks Signals with Junction Indicators outside tracks Setting distances of OHE masts shall be in accordance with Drg.No.22-D7. 22.3.6 Signals with Junction Indicators between Tracks (a) Precautions and parameters for location of portal drop arms shall be as specified under Para 22.3.4. (b) For details of drawings, illustrating the above principles for Colour Light Signals, refer to Drg.No.22-D7. 22.3.7 The visibility of the signal shall be checked by day as well as by night by the Official in charge (Signal) of the section after each phase of the O.H.E work, i.e. erection of masts, provision of brackets, wiring, etc. If at any stage the official feels that the visibility is not adequate, he shall impose suitable speed restrictions and take such steps as are required to improve the visibility. Note: For Details on Cable laying in RE Area, please Refer to Chapter 15 of SEM. 22.3.8 For Clearances for Signals for High Rise OHE (for Running Double Stack Container & Three Tier Car) , Please see Annexure: 22-A3 and Drg.No.22-D7 Chapter 22: Requirements Of Signalling In 25 KV AC Electrified Area Page 478 of 530