Lars Buhrkall

Freelance Electrical Engineer

Electrical Drives, Traction Systems, and Electromagnetic Compatibility

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This page contains some PDF documents that you may downloaded for free. Please let me have your comments if you find any errors.

Traction System Case Study
Ice on the Overhead Line
Problems and Countermeasures in Traction Systems

Traction System Case Study
I have made a presentation called 'Traction System Case Study' at the most recent IEE courses on electric traction systems. The general theme of the presentation is the most costly mistakes I have seen during my 20 years as an electrical traction engineer.

From the abstract:

The development of a cost-optimal traction system towards a specific set of customer requirements is a complex, iterative process with many pitfalls.  The new European market situation, with business-oriented operators specifying only their basic performance requirements and no technical details, and with a multinational industry where components such as motors, inverters, etc. are supplied not only from different departments but from different countries, increases the complexity of the process even further, and with that the risk of sub optimisation.  Even in the simplest case, with the only requirement being a maximum run time between two stations with a certain train weight, several very different solutions are all technically possible.

 Among the most important (costly!) trade-offs that must be balanced are:

 * The number of traction motors vs. the installed traction power;

 * Traction motor size, rated power of the 3-phase inverter, and traction motor cooling system;

 * Interference requirements and AC and DC line filters;

 * DC link voltage, main transformer layout, and line converter design;

 * Step-up choppers or direct supply from the DC line

The paper and the overhead slides can be downloaded here:
Traction System Case Study Paper
Traction System Case Study OHs.


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Ice on the Overhead Line
Some of the documents from the ESC UserGroup project 'Ice on the OHL' are available for free download. This project was formed in order to analyse, describe, and if possible suggest solutions the problems that are seen at conditions with ice on the overhead line of AC electrified railways. Amongst these problems are
the generation of DC components and even harmonics in the line current that may potentially interfere with track circuits operated by DC or by an even harmonic such as 100 Hz at 16.7 Hz supply frequency.

If you want the full documentation, please send me an email with name and postal address, and I will send you a CD-ROM.
Summary Report
Summary OH series
CRREL report on 'Icing on Structures
Meteorological Conditions Causing OHL Ice
Analysis of AC OHL ice recordings


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Problems and Countermeasures in Traction Systems
First a note that lists EMC-issues and known problems:
Compatibility Between Infrastructure and Vehicles

Then a short note that describes in general terms the four most important problems related to AC-AC traction:
1. Amplification of PWM harmonics
2. "Active" vehicle impedance and control system instability
3. Interharmonic modulation and "Harmonic Avalanche"
4. Power control and line voltage collapse
General Problems of AC-AC Traction

This is an OH series that goes through the problems and countermeasures related to electrical resonances between the vehicle and the supply system, and the amplification of PWM harmonics.
OH Series AC Line Harmonics

This is a rather basic note on power control of AC-AC vehicles, explaining how it is possible to use regenerative braking even on long supply lines without exceeding the maximum line voltage limits.
Power Control of AC-Supplied Rail Vehicles

This note explains why the low-frequency power oscillations that are sometimes seen in the rather weak 16.7 Hz railway power supply network in Scandinavia do not cause interference with DC track circuits.
Power Oscillation In Time And Frequency Domain

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Latest update: 06.09.2014