Traction Transformers – "Tractronic®"

The perfect transformer for every vehicle 

Siemens Energy offers single-phase and multi-phase units in all capacity ranges up to 15 MVA and – upon your request – even above. Designing and manufacturing traction transformers for rail operators and train manufacturers worldwide, Siemens produces TT transformers thatincrease train efficiency and performance - handle highest ratings in a minimum of available space - serve local content demands for worldwide application - afford maximum reliability and flexibility.

Transformer Magazine Interview, April 2021

Interview with Tilo Else, Siemens Energy's Vice President for Distribution Transformers

The energy market is rapidly evolving with the energy transition as one of the most fundamental changes: What challenges does this rapidly changing energy landscape pose for customers?

Please click on the link to read the complete interview
Technology & Benefits

We cover every of your preference

With over a century of experience in transformer technology, Siemens Energy is one of the world’s leading suppliers for customized, state-of-the-art railway transformers. The secret to Siemens stellar track record is a refined system of global logistics, internationally binding quality standards, highly trained skilled workers and specialization. Units can be mounted in machine rooms, as low-floor designs, on the roof, or under the floor. Traction transformers of Siemens Energy are available in all relevant ratings, with frequencies from 16 ⅔ to 60 Hz and rated power up to 15 MVA. Operating voltages include 1.5 kV DC, 3 kV DC, 12 kV, 15 kV, 25 kV as well as special voltage levels. The focus is on maximum reliability, economic efficiency and safety – and ensuring that the transformers are perfectly in line with the customer’s requirements.

Compact, light and efficient


Choose between different design options.


  • power ratings – frequency, capacity and voltage
  • size, weight and place of installation
  • dissipation and short-circuit voltages
  • losses and impedance voltage characteristics
  • driving patterns and medium-frequency performance
  • materials and technologies to meet environmental requirements (e.g. ester coolant)    


Rely on Siemens Energy Transformers – anywhere, anytime

Siemens Energy traction transformers operates a worldwide manufacturing and service network to serve customers all over the world. Our manufacturing sites worldwide adhere to European quality and sustainability standards – regardless of the manufacturing location.

  • trustful and responsible partner with solid installed base worldwide,
  • state-of-the art transformers technology, 
  • tailored solutions for customer’s requirements,
  • comprehensive service offering directly on-site.

Leveraging data for maximum transformer performance

Trasction transformers from Siemens Energy offer the opportunity to track the transformers in operation. Operators can not only monitor but optimize transformer performance. Monitoring and data analysis are the important factors for digitalization of traction transformer for rollingstock applications.

A modular multisensory system continuously monitors the “health” status of the transformer and modifies operation behavior according to the results of an onboard optimization algorithm. The Siemens monitoring system leverages a new generation of sensors. These sensors transmit data to a local, remote or cloud-based control system. After data processing, the actors will – if necessary – receive commands for correcting the operation behavior.

Economical and technical information of each traction transformer is updated online and collected to optimize all similar transformers in operation. Our real-time monitoring system optimizes cost of operation cost and maintenance intervals, increasing energy and economic efficiency.

Developed, tested and certified

Siemens traction transformers are setting standards of quality and versatility around the world. Close cooperations with international standards committees guarantee the compliance with the specific requirements and standards.


Siemens is a founding member of the IRIS Initiative, and consistently implements its requirements. Our railway components comply with all the relevant standards, for example: DIN, EN, IEC, IEEE, ISO, EAC / GOST and ANSI, as well as the current fire protection standard EN 45545. With our certified components, we actively support the worldwide vehicle approval process; hence our traction transformers comply with all relevant standards, for example:


  • DIN EN ISO 9001
  • DIN EN ISO 14001
  • OHSAS 18001
  • EN 15085-2 CL 1
  • GOST
  • IRIS

Tests for maximum reliability and customer satisfaction

Siemens uses the most advanced and comprehensive routine tests, type evaluations and special tests for maximized product reliability and customer satisfaction. Siemens traction transformers are tested essentially in the same way as power transformers to ensure maximum safety and quality.

  • Measurement of winding resistances
  • Measurement of ratios and proof of polarity
  • Measurement of idling dissipation and idling current
  • Measurement of relative short-circuit voltage,
  • short-circuit dissipation and total dissipation
  • Testing with applied power-frequency withstand
  • voltage (testing of winding)
  • Testing with induced power-frequency withstand
  • voltage (testing of winding)
  • Testing of step switch/tap changer (if present)
  • Inductance measurement on a case-by-case basis

Type evaluations examine different transformer properties, normally these are measurements of heating and lightning impulse voltage testing. For measurement of heating, losses are fed in based on the preceding measurement and subsequent types of operation. In the process, differing oil temperatures and the coolant temperatures (i.e. air/water) are recorded. The winding temperature is determined indirectly based on winding resistance. It measured after the feed-in has been terminated. Pressure and throughflow measurements within the cooling circuit can also be subject of an evaluation. In transformers fed straight from the overhead lines, the high-voltage winding undergoes a lightning impulse voltage test.

  • Measurement of magnetic field strength at different
  • distances from the tank wall in three orthogonal directions
  • Noise measurements
  • Partial discharge measurement
  • Mathematical proof of sudden short-circuit resistance.
  • Upon request, tests may be performed at an accredited third-party laboratory.
Areas of application

Turning energy into speed

On-board traction transformers transform energy into speed that moves passengers and freight. As a part of the traction chain, they are crucial to the performance of train and operator services. Siemens Energy designs and builds traction transformers in different specification profiles. Every traction transformer type is assembled for a special type of train.

With ultra light “Thinity” transformers

With Tractronic AC and DC transformers

With Tractronic AUX transformers

With TT transformers

With TT transformers

With TT transformers

Downloads and services

Make use of our services

For your convenience, we have gathered relevant downloads in one spot.
Compliance statement

Siemens Energy complies with the laws and regulations affecting traction transformers

Siemens Energy is closely monitoring the development of transformer regulations worldwide e.g. European Eco Design Directive and US DOE rules. Siemens Energy adheres to the rules and regulations communicated e.g. in US and Europe and complies with all relevant requirements for every transformer product delivered. As a trustful and responsible partner Siemens Energy understands the importance of these regulations and will continue to monitor potential future requirements. We will continue to adapt and comply with all relevant regulatory changes.