Technical Details – Traction Transformer
1. Overview
A Traction Transformer is a specialized type of transformer designed to supply power to electric locomotives or train sets. It steps down high-voltage AC from overhead lines or substations to lower voltages suitable for traction motors or power electronics like inverters and converters.
2. Applications
- Electric locomotives (AC, DC, or multi-system)
- EMUs (Electric Multiple Units)
- Metro and suburban rail systems
- High-speed rail systems
- Railway substations
3. Key Electrical Specifications
|
Parameter
|
Typical Value
|
|---|---|
|
Primary Voltage
|
15 kV, 25 kV, 50 kV (depending on rail system)
|
|
Secondary Voltage
|
1.2 – 3.3 kV (for motor converters), sometimes multiple taps
|
|
Frequency
|
16.7 Hz (in Europe), 50 Hz or 60 Hz
|
|
Power Rating
|
1 MVA – 10 MVA (mobile); up to 100 MVA (fixed substations)
|
|
Phases
|
Single-phase (most common), or three-phase for specific systems
|
|
Cooling Methods
|
ONAN, ONAF, OFAF, or forced air/water for onboard units
|
4. Design Features
a. Onboard (Locomotive) Traction Transformers
- Compact and lightweight design to fit within locomotive body
- Forced cooling systems (oil or water cooled) due to limited airflow
- Multi-secondary windings for various subsystems:
- Power to traction converters
- Auxiliary power supply (lighting, HVAC)
- Battery chargers, control electronics
b. Substation Traction Transformers
- Step down high-voltage grid supply to catenary voltage
- Designed for high short-circuit withstand, and frequent overloads
- Often paired with phase converters or Scott-T transformers for single-phase traction load
5. Mechanical Features
- Vibration and shock resistance for onboard types
- Compact size to fit between bogies or inside chassis
- High dielectric insulation for steep voltage transients from switching
- Fire-resistant design for passenger safety (e.g., dry-type insulation in metros)
Winding Configurations
- Single-phase primary (connected to catenary via circuit breaker)
- Multiple secondaries for motor drives and auxiliaries
- Sometimes tapped primaries for voltage regulation
Protection and Monitoring
- Buchholz relay (for oil-filled units)
- Oil temperature and winding temperature sensors
- Differential and overcurrent protection
- Surge arresters and insulation monitoring
Standards and Certifications
- IEC 60310 – Railway applications – Traction transformers and inductors
- IEC 60076 – Power transformers (general)
- EN 45545 – Fire protection on railway vehicles
- IS 2026 (Indian standard)
- IEEE Std C57 series (for power and traction transformers)
Advantages
- High efficiency under cyclic load
- Robust insulation for high-speed switching
- Designed for overloads and regenerative braking energy
- Multiple outputs with galvanic isolation
Traction Transformer vs. Power Transformer
|
Feature
|
Traction Transformer
|
Power Transformer
|
|---|---|---|
|
Load Type
|
Highly dynamic, cyclic
|
Steady or slowly varying
|
|
Cooling
|
Often forced air/water
|
Typically oil/air cooled
|
|
Voltage Regulation
|
Via tap changers or inverters
|
OLTC or fixed taps
|
|
Vibration Resistance
|
High (onboard use)
|
Moderate
|
|
Application
|
Locomotives, EMUs, metros
|
Substations, grids
|
CONNECT WITH VOLTAMP®