Power from the overhead catenary reaches the underframe-mounted main transformer via the pantograph. After the transformer, the traction circuit splits into two separate circuits, each feeding its own traction converter — the converter can conduct current from catenary to traction motor (traction mode) or, in reverse, from motor to catenary (braking mode, motors acting as generators). Three 3-phase asynchronous traction motors connect in parallel to each converter.
WAG9 Power Circuit — Real Specifications
- Traction winding: 2.1 mH inductance, 59.4% of transformer capacity.
- Line-side parameters: 1269 Vrms, 1142 Amps.
- Pre-charging resistance: 50 Ω. DC Link capacitance: 11.4 ± 0.6 mF. MUB resistance: 2.5Ω ± 5%.
- Resistor harmonic filter: 0.2 Ω / 60 kW, 2800V. Capacitor harmonic filter: 0.8 mF / 2500V. Inductance harmonic filter: 0.29mH.
- Harmonic winding: 400 kVA, 1154V, 347A. Auxiliary winding: 1000V, 334 kVA.
- Series resonant circuit choke: 0.551 mH. Its capacitor bank: 4.6 mF.
The 22-Component Power Circuit Path
The complete power circuit, in order, from pantograph to traction motor: (1) Pantograph, (2) Primary voltage transformer, (3) Earthing switch VCB, (4) Main circuit breaker/VCB, (5) Primary current transformer, (6) Transformer, (7) Contactor filter ON/OFF, (8) Resistor harmonic filter, (9) Surge arrestor, (10) Earth return brush, (11) Earthing choke, (12) Valve set 2×ZV, (13) Contactor converter precharging, (14) Contactor converter, (15) Valve set ZV+MV, (16) Precharging resistor converter, (17) Resistor over voltage protection, (18) Series resonant circuit choke, (19) Capacitor bank series resonant circuit, (20) Capacitor bank DC-link, (21) Earthing switch DC-link, (22) Traction motor, with the capacitor bank harmonic filter (23) tapped off separately.
Potential Transformer (Primary Voltage Transformer)
Located on the converter roof hatch, attached to the pantograph via the roofline. It steps down catenary voltage (~25kV) to 200V AC, then a resistor divides this into three separate output signals: 4V AC to the main converter electronics, 10V DC to the catenary voltmeter on the driver's console, and a third feed to the Minimum Voltage Relay.
Real Power-Flow Narrative — Windings, DC Link & Regeneration
WAP5 and WAG9 both use 3-phase drive with GTO thyristors and microprocessor-based control. The main transformer's primary winding is fed from the OHE (25kV single-phase AC, 50Hz) through the pantograph and VCB; two surge arresters protect the roof — one at the pantograph end, one after the VCB. A primary voltage transformer continuously monitors catenary voltage for the control electronics, which trips the VCB if catenary voltage goes out of limits.
The main transformer is a specially-built high-impedance transformer (vs conventional-loco transformers): besides the primary winding, it has 4 real traction windings and 1 auxiliary winding, plus a harmonic-filter winding with its own filter to reduce harmonics; WAP5 additionally has a hotel-load winding. Each group of 2 traction windings feeds two 4-quadrant line converters connected in parallel; these feed an intermediate DC-link circuit (series resonant circuit + DC-link capacitors), which supplies the drive converter. The drive converter feeds 2 traction motors per bogie on WAP5, and 3 traction motors per bogie on WAG9. Traction motors discharge instantaneously through the MUB resistor; GTO firing is controlled by the control electronics.
During regenerative braking, traction motors act as induction generators by controlling output frequency to obtain a negative slip value. In the line converter, the resulting 3-phase electrical energy converts to single-phase energy through the DC link and feeds back to the catenary via the main transformer. Thanks to the 4-quadrant pulse-controlled converter, fundamental reactive power flow can be adapted to line-voltage conditions independent of active power flow — so the converter also stabilises line voltage.
WAP5 & WAG9 — Real Subsystem Component Data
| Subsystem | WAP5 (Real) | WAG9 (Real) |
|---|---|---|
| Traction motor make/type | ABB Switzerland, 6FXA7059 (4/loco) | ABB Switzerland, 6FRA6068, axle-hung nose-suspended (6/loco) |
| Motor continuous/max torque | 6930 / 9920 Nm | 6330 / 9200 Nm |
| Motor continuous/max output | 1150 kW | 850 kW |
| Motor cos φ | 0.86 | 0.88 |
| Motor design speed / overspeed test | 3571 rpm | 2842 rpm design / 3250 rpm overspeed test (2 min) |
| Stator winding insulation | Class 200, Veridur (R) system | Class 200, Veridur (R) system |
| Transformer make/type | ABB Switzerland, LOT 7500 | ABB Switzerland, LOT 6500 |
| Transformer primary rating | 25kV, 7475 kVA, 299A | 25kV, 6531 kVA, 261.25A |
| Traction winding rating (×4) | 1269V, 1449 kVA, 1142A each | 1269V, 1449 kVA, 1142A each |
| Aux. converter winding | 1000V, 334 kVA, 334A | 1000V, 334 kVA, 334A |
| Hotel load winding | 750V, 945 kVA, 1260A | — (not applicable, freight loco) |
| Filter winding | 1154V, 400 kVA, 347A | 1154V, 400 kVA, 347A |
| Transformer cooling | Forced oil cooling, Diala DX mineral oil | Forced oil cooling, Diala DX mineral oil |
| Power converter make/type | ABB Switzerland, UW 2423-2810 (2/loco) | Similar to WAP5 |
| 4Q converter DC-link voltage | 2800V nominal | 2800V nominal |
| 4Q converter GTOs/diodes | 8 GTO thyristors (4.5kV/3kA, Toshiba SG3000GXH24 or equiv.) + 8 power diodes (D921S45T Eupec or equiv.) | Similar to WAP5 |
| Motor inverter GTOs/diodes | 6 GTO thyristors (4.5kV/3kA, same type) + 6 power diodes (same type) | Similar to WAP5 |
| DC-link capacitor make/type | Condis CDM15230A0815, 815μF/2940V, bank 11.41mF | Similar to WAP5 |
| MUB (instant voltage limitation) | Microelettrica Scientifica (Italy), 2800V/500A, contains 1 GTO + power diode + power resistor | Similar to WAP5 |
| Series resonant circuit capacitor | ERO-GFP 3.8, 560μF/2940V, bank 4.6mF (8 caps, one adjustable unit of 3: 280+140+140μF) | Similar to WAP5 |
Main Transformer
25kV single-phase AC from OHE, via pantograph/roof equipment/VCB, charges the main transformer where it's stepped down to various operating voltages. The tank is filled with transformer oil (APAR or Shell Diala DX) to boost insulation strength and provide cooling.