Application of SVG in voltage compensation of railway traction network

Background:
Electrified railway has the advantages of high speed, heavy load, high energy efficiency and good economic benefits, so it is widely used in railway system. There are mainly two types of railway traction load: AC-DC and AC-DC-AC electric locomotives. AC-DC trains are generally used for freight and ordinary passenger trains, while AC-DC-AC trains are mainly used for high-speed railway system. At present, Russian electrified railway locomotives adopt the traditional AC-DC transmission mode. When the train is running, it will produce a lot of reactive power and odd harmonic current. Reactive power causes low voltage of traction network line, which leads to the decline of train operation efficiency. Harmonic current causes abnormal line voltage, which is not conducive to the safe and stable operation of equipment.

RXPE solution

In order to solve the above-mentioned power quality problems on site, RXPE provided five sets of 27.5kV cascade SVGs for the Russian Federation railway company in September 2017, with equipment capacity of 10MVar. The equipment is installed at the midpoint of the traction network line to provide fundamental voltage support for the line and compensate the harmonic voltage.



Schematic diagram of SVG installation position

SVG device photos

Key technology 

1. It does not need to sample the power grid or load current directly, we can sample access point voltage only, which solves the problem of grid harmonic voltage distortion caused by load harmonics;

2. The short-wave communication mode is adopted by the on-site railway locomotive. After operation starts, the du/dt generated by IGBT device switch will interfere with the existing communication system, so it is necessary to install a passive filter to eliminate the interference;



SVG control block diagram

Operation effect

After SVG starts operation, the grid voltage is stable, the minimum value of 27.5kV busbar voltage is increased from 0.85pu to 0.94pu, the train operation efficiency is increased by 10%, and the grid voltage THD is less than 4%.

Grid voltage and SVG current curve (before SVG operation)

Grid voltage and SVG current curve (after SVG operation)



Waveform of grid voltage / SVG current after compensation

Grid voltage and SVG current waveform (after SVG operation)

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