Lars Buhrkall

Freelance Electrical Engineer

Electrical Drives, Traction Systems, and Electromagnetic Compatibility

Photo gallery




This section provides a brief introduction to the general services I can offer. If your specific problem is not on the list, don't run away - send me an email about it, and let's see what can be done!


  1. Calculation of Line Interference Currents
  2. Measurements and Data Analysis
  3. Interaction Between Vehicle and Power Supply
  4. Fault Analysis, Demonstration of Compatibility, and Safety Case
  5. Fault Tracking
  6. General Propulsion System Engineering

Calculation of Line Interference Currents

It is crucial to get a quantitatively correct prediction of the levels of line interference currents that will be generated by a new rail vehicle already at the design stage. Such a calculation must include all parts of the overall system, i.e., the generating vehicle(s), the power supply, the transmission line character of the overhead line or 3rd rail, other vehicles, etc., all at any relevant operation condition.

Typically, such calculations are made in a Monte-Carlo type of analysis, by means of a computer program that runs through thousands of calculation loops with a quasi-random variation of all parameters before each loop. In this way, both the normal statistical distribution of the interference current levels and the theoretical worst-case can be predicted.

These calculation principles are also very suitable for analysing the effects of parameter variation, for example due to component ageing or fault conditions.

Back to top

Measurements and Data Analysis

I have a small portable PC-based set of equipment for data acquisition. This equipment has successfully been used for approval testing of locomotives, and is also ideal for fault-tracking. In the picture below, the equipment is installed in the driver's cab of a BR185.

I am also often doing the analysis of data that have been recorded by others, either on a PC or on a DAT recorder.I have experience from preparing, planning and executing test campains with railway vehicles in several countries, and from doing the data analysis according to the local requirements.

Back to top

Interaction Between Vehicle and Power Supply

This includes the analysis of problems like:
- Power oscillations
- Rating and characteristica of line protection relays
- Transient overvoltages
- Power limitations
- Ice on the supply conductor
- Active and reactive power in driving and braking
- Etc.

Back to top

Fault Analysis, Demonstration of Compatibility, and Safety Case

It is no longer considered satisfactory to show by measurements that a locomotive works according to the specification on the day it is delivered. Today it must be demonstrated that the vehicle will operate safely throughout its entire lifetime. This proof makes use of technical disciplins like Fault Tree Analysis (FTA) and Failure Modes, Effects and Criticality Analysis (FMECA), but in particular a thorough experience and understanding of the mechanisms that may lead to unsafe operation (e.g., by increasing the interference current levels) is required.

The overall proof (which is documented in the Safety Case) must be supported not only by theoretical analysis but also by adequate tests and measurements. The overall activity must be carefully planned and managed.

Back to top

Fault Tracking

Why doesn't this system operate correctly, or why doesn't this specific device work as it should? Well, I'll be happy to have a look at it!

Back to top

General Propulsion System Engineering

If you have a temporary shortage of people in your department for converters or propulsion systems in general, I can fill in on most places!

Back to top

Please feel free to send an e-mail to with comments or questions to this website.
Latest update: 06.09.2014