Indian Railways electric locomotives run on two historic supply systems — 25kV 50Hz AC (phase via catenary, neutral/earth via track) and 1.5kV DC (positive via catenary, negative/earth via track) — though DC traction has now been almost entirely phased out in favour of AC. Locomotive naming follows a consistent scheme: the first letter is gauge (W = broad gauge), the second is supply type (A = AC, C = DC, CA = dual AC/DC), and the third is service (M = mixed, G = goods, P = passenger).
Historical Progression
- DC classes: WCG2 (Goods), WCM6 (Passenger) — 1.5kV DC.
- Dual AC/DC classes: WCAM1, WCAM2, WCAM3 (Mixed service), WCAG1 (Goods) — for sections with both electrification types.
- Conventional AC classes: WAM4 (Mixed), WAG5 & WAG7 (Goods), WAP1-4 (Passenger) — all DC-series-motor, tap-changer technology.
- 3-Phase AC classes: WAP5 & WAP7 (Passenger), WAG9 (Goods) — IGBT/GTO-based, induction motor technology, the current mainline workhorses.
- Newest classes: WAG-11 (rebuilt from diesel WDG-4 platform with GTO propulsion, using WAG9-derived control since 2018) and WAG D-9 (Siemens-built at Dahod, 12000 HP class, dual pantograph, Kavach ATP and Vigilance Control built in from the factory, since 2023).
Current Fleet — Comparative Technical Data
| Class | Service | Max Speed | Power (Continuous HP) | Traction Motor |
|---|---|---|---|---|
| WAP5 | Passenger | 160 kmph | 5440 HP | 4 × 6FXA7059 |
| WAP7 | Passenger | 140 kmph (rated); IR-restricted 130 | 6120 HP | 6 × 6FRA6068 |
| WAG9 | Goods | 100 kmph | 6120 HP | 6 × 6FRA6068 |
| WAG7 | Goods (older, conventional) | 105 kmph | 5000 HP | Hitachi HS15250A/G |
| WAG-11 | Goods (rebuilt platform) | — | 1000 HP per motor (12 motors) | GT46MAC-derived (ex-diesel) |
| WAG D-9 | Goods (newest, Siemens) | 120 kmph operational (135 tested) | ~12,000 HP class | Siemens MoComp |
Exam Focus — WAP7 & WAG9 Share the Same Traction Motor
Both WAP7 and WAG9 use exactly the same traction motor type (6FRA6068, 6 motors, 850kW continuous each) — the difference between them is gear ratio (72:20 for WAP7's higher speed/lower effort, versus WAG9's freight-optimised ratio) and bogie/body design, not the motor itself.
Conventional vs 3-Phase — Point-by-Point Comparison
| Feature | Conventional Loco | 3-Phase Loco |
|---|---|---|
| Traction motor | DC series motor (field & armature windings, commutator, brushes — more parts, more maintenance) | 3-phase induction motor (stator & rotor only — fewer parts, less maintenance) |
| Control system | Electrical traction control (more wiring, relays; hardware changes needed for modification) | Digital electronics, real-time traction control — software controlled, easy functional changes |
| Weight transfer | Manual — ZQWC (weight transfer control) closed manually, reduces TE via field weakening of leading bogie | Automatic — traction converter senses each motor's RPM and shifts TE from leading to trailing bogie automatically |
| Wheel slip handling | Reduce TE by pickup, regress notches, increase adhesion by sanding — no automatic brake application | Anti-spin protection — when requested/effected TE ratio drops below 0.5, automatically reduces TE and applies light brakes |
| Fault diagnosis | Not existing — requires manual troubleshooting by crew | On-board fault diagnostic system — eliminates/simplifies troubleshooting via screen display |
Real Fleet Technical Data
The comparative tables below give exact technical-spec figures for each class.
| Description | WAM4 | WAP1 | WAP4 | WAP5 | WAP7 | WAG5 A/B | WAG5 HA/HB | WAG6 | WAG7 | WAG9 | WAG9H |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Continuous HP | 3640 | 3800 | 5000 | 5440 | 6120 | 3850 | 3850 | 6000 | 5000 | 6120 | 6120 |
| Max Speed (kmph) | 110 | 130 | 140 | 160 | 140 | 105/100 | 105/100 | 80 | 120 | 100 | 100 |
| Starting TE (Tonnes) | 30.0 | 22.4 | 32.4 | 26.29 | 32.88 | 33.5 | 33.5 | 46.0 | 44.0 | 46.89 | 52.0 |
| Continuous TE (Tonnes) | 17.6 | 13.8 | 18.8 | 22.42 | 23.23 | 20.6 | 20.6 | 32.0 | 27.0 | 33.12 | 46.0 |
| Total Weight (Tonnes) | 112.8 | 108.3 | 112.8 | 78.0 | 123.0 | 118.8 | 123.0 | 123.0 | 123.0 | 123.0 | 132.0 |
| Braking | Air | Air | Air | Air+Regen | Air+Regen | Air | Air | Air | Air | Air+Regen | Air+Regen |
| Bogies | Co-Co | Co-Co | Co-Co | Bo-Bo | Co-Co | Co-Co | Co-Co | Bo-Bo-Bo | Co-Co | Co-Co | Co-Co |
| Traction Motor | TAO-659+TAOchi | TAO-659 | HS-15250A | 6FXA-7059 | 6FRA-6068 | TAO-659+TAOchi | HS-15250A | ASEA L3M450-2 | HS-15250A | 6FRA-6068 | 6FRA-6068HT |
| No. of Traction Motors | 6 | 6 | 6 | 4 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
| Gear Ratio | 58:21 | 58:21 | 23:59 | 67:35:17 | 20:72 | 62:15 | 64:18 | -- | 65:16 | 77:15 (5.133) | (5.4) |
| Wheel Dia New/Worn (mm) | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 | 1092/1016 |
| Max Regen Braking Effort (KN) | — | — | — | 160 | 182 | — | — | — | — | 260 | — |
| Description | WCAM-1,2 & 3 | WCM-6 | WCAG-1 |
|---|---|---|---|
| Supply System (kV) | 25 at 50Hz AC / 1.5 DC | 25 at 50Hz AC / 1.5 DC | 25 at 50Hz AC / 1.5 DC |
| Continuous HP | 3840/2930 | 4600 | 5000/4600 |
| Max Speed (kmph) | 120 | 105 | 100 |
| Starting TE (Tonnes) | 33.4/28.2 | 39.6 | 44/30 |
| Continuous TE (Tonnes) | 16/22.6 | 27 | 31/30 |
| Total Weight (Tonnes) | 112.8 | 120 | 128 |
| Braking | Air | Air | Air |
| Bogies | Co-Co | Co-Co | Co-Co |
| Traction Motor | TAO-659 + TAOchi + HS15250 | HS15250-A | HS15250-A |
| No. of Traction Motors | 6 | 6 | 6 |
| Gear Ratio | — | 18:64 | — |
| Wheel Dia New/Worn (mm) | 1092/1016 | 1092/1016 | 1092/1016 |
Exam Focus — Dual-Voltage Classes Are Now AC-Only
WCAM-1/2/3, WCM-6, and WCAG-1 were built as dual AC/DC (25kV/1.5kV) locos, but there is presently no DC traction anywhere on Indian Railways — these locos now run permanently on AC traction with their DC-side circuits isolated. WAP5 stands out in the fleet table as the only Bo-Bo (not Co-Co) 3-phase class and has the lowest total weight (78 tonnes) despite high continuous HP (5440) — both consequences of its lighter, high-speed passenger-hauling design.