Technology Railway Signaling Systems
Railway Signaling Systems – RRB Technology GK Capsule
1. Signaling in Indian Railways – At a Glance
| Parameter | Statistic (2024) |
|---|---|
| Route Km under signaling | 65,000 km |
| Stations with Panel/Route-Relay Interlocking | 6,800+ (≈ 95 %) |
| Stations with Electronic Interlocking (EI) | 1,450+ |
| Automatic Block sections (Track-circuit based) | 3,800 km |
| TPWS / Kavach fitment (Locos) | 2,700 locos |
| Data-loggers installed | 5,300 stations |
| LED signals commissioned | 92 % of total colour-light signals |
| 60 kg / 52 kg rail used in block sections | 98 % |
2. Evolution & Hierarchy of Indian Railway Signaling
| Era | Dominant System | Salient Features |
|---|---|---|
| I (1853-1920) | Mechanical lower-quadrant semaphore | Wire-pulled levers, 2-aspect |
| II (1920-1960) | Upper-quadrant semaphore & 3-aspect | Electric lamp, 3-position |
| III (1960-1990) | Colour-light Multiple-Aspect (MACLS) | 4-aspect, relay logic |
| IV (1990-2010) | Panel / Route-Relay Interlocking | Centralised cabin, 4-aspect |
| V (2010-onwards) | Electronic Interlocking + TPWS/Kavach | Computer-based, cab-signalling |
3. Signal Aspects, Indications & Speeds (4-Aspect MACLS)
| Aspect | Colour | Indication | Speed to be followed |
|---|---|---|---|
| Green (G) | Green | Clear – next two blocks free | Maximum sectional speed |
| Double Yellow (DY) | Two Yellow | Caution – next signal at Yellow | 60 km/h or 50 % of max |
| Yellow (Y) | Single Yellow | Attention – next signal at Danger | 30 km/h / 15 km/h while approaching |
| Red (R) | Red | Stop – dead end | 0 km/h |
4. Types of Block Systems
| Block Working | Method | Max. Speed Permitted | Line Capacity Gain |
|---|---|---|---|
| Absolute Block (AB) | Token / Paper line-clear | 160 km/h | Base |
| Automatic Block (Auto) | Track-circuit / Axle-counter | 160 km/h | 15-20 % |
| Centralised Traffic Control (CTC) | Real-time remote | 160 km/h | 25 % |
| Moving Block (Kavach) | Radio-based | 160 km/h | 30 % |
5. Interlocking Technologies – Comparison
| Feature | Mechanical | Route-Relay | Electronic Interlocking (EI) |
|---|---|---|---|
| Logic medium | Lever & locking tray | Plug-in relays | Microprocessor / FPGA |
| Time to set route | 8-12 s | 3-5 s | 1-2 s |
| Failure recovery | Manual | Manual | Automatic hot-standby |
| Max. routes per station | ≈ 50 | ≈ 200 | 1,000+ |
| Safety integrity level | SIL-0 | SIL-2 | SIL-4 (CENELEC) |
6. Train Protection & Cab-Signalling
- TPWS (Train Protection & Warning System) – on-board magnets & balises; enforces 160 km/h.
- Kavach – indigenised ATP; works on LTE-R; SIL-4; target: 3,000 km Golden-Quadrilateral by 2025.
- ETCS Level-2 (planned) – Euro-radio; continuous cab-signalling; 200 km/h on Dedicated Freight Corridors.
7. Data-Logger, OFC & Integrated Power Supply
- Data-logger: micro-based fault-cum-event recorder; 96 h memory; RS-485 port.
- OFC backbone: 64-core optic-fibre along 60,000 Rkm; SDH & MPLS-TP.
- IPS (Integrated Power Supply): 110 V DC ±10 %; battery back-up 2 h full load; SMPS technology.
8. Exam-Friendly Lists
a. Signal Gear – Standard Quantities
- Point machine: 220 V DC / 110 V AC dual-voltage
- Track circuit: 50 V DC / 10.5 V DC (audio-frequency)
- Axle counter: 30 V DC; reset time 2 s
- LED signal: 25 W cluster; life 1,00,000 h
b. RDSO & International Standards
- IRS: S-23 (relay), S-35 (EI), S-99 (Kavach)
- CENELEC: EN-50126/8/9 (RAMS)
- UIC: 541-3 (colour-light), 544-1 (ATP)
9. Frequently Asked Facts
- First electric signal in India: 1928 – Bombay VT–Bandra
- Longest automatic block section: 17 km – Jhansi–Babina (UP)
- First Electronic Interlocking commissioned: 1997 – Virar (WR)
- Kavach development agency: IRSE/ RDSO / HBL-IR
- Target for 100 % EI: 2030 (Indian Railway Vision-2030)
15 MCQs for RRB CBT-2 / ALP / Tech
| Q. | Question | Options | Correct |
|---|---|---|---|
| 1 | What is the normal voltage of DC track circuit on Indian Railways? | a) 110 V b) 50 V c) 24 V d) 12 V | b |
| 2 | Which aspect in MACLS allows train to run at maximum sectional speed? | a) Yellow b) Double Yellow c) Green d | c |
| 3 | The minimum SIL level prescribed for Electronic Interlocking is | a) SIL-1 b) SIL-2 c) SIL-3 d) SIL-4 | d |
| 4 | Kavach ATP system works on which radio band? | a) GSM-R b) LTE-R c) Wi-Fi d) TETRA | b |
| 5 | The first station in India to have Electronic Interlocking was | a) Delhi b) Virar c) Howrah d) Chennai | b |
| 6 | Which of the following is NOT a standard colour in 4-aspect signalling? | a) Green b) Yellow c) Double Yellow d) Blue | d |
| 7 | In Absolute Block system, authority to proceed is issued as | a) Token b) Paper line-clear c) Both d) None | c |
| 8 | The maximum route setting time in Route-Relay Interlocking is about | a) 1 s b) 3-5 s c) 8 s d) 12 s | b |
| 9 | LED signal cluster consumes approximately | a) 8 W b) 15 W c) 25 W d) 50 W | c |
| 10 | Which block system gives the highest line capacity? | a) Absolute b) Automatic c) CTC d) Moving Block (Kavach) | d |
| 11 | Integrated Power Supply provides stabilized DC of | a) 12 V b) 24 V c) 60 V d) 110 V | d |
| 12 | Axle counter reset time is normally | a) 0.5 s b) 2 s c) 5 s d) 10 s | b |
| 13 | Which RDSO specification deals with Kavach? | a) IRS:S-23 b) IRS:S-35 c) IRS:S-99 d) IRS:S-45 | c |
| 14 | The optic-fibre backbone along tracks is laid with minimum cores of | a) 24 b) 48 c) 64 d) 96 | c |
| 15 | As on 2024, approx. what % of stations are covered by Electronic Interlocking? | a) 10 % b) 20 % c) 30 % d) 40 % | b |
Quick-Review Q&A – Signal Failure Codes
Q: What does "DSP" mean in data-logger print? A: "Drop in Signal Power" – LED fuse blown or 110 V feed failure.Q: Which relay contact proves “points locked”?
A: NWKR (Normal Wicket Key Relay) or RWKR for reverse.
Q: Minimum overlap length in automatic signalling?
A: 120 m (or 180 m for speeds > 130 km/h).
Revise → Rehearse → Crack the RRB!
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