SVC Light® for railway load balancing
The growth of train traffic and the increased speed of trains in France is resulting in deterioration of power quality in the electric power systems feeding the railways. This is the case in particular for voltage unbalance, produced by single-phase connection of railway substations to the national three-phase power transmission and sub-transmission grid.
Evron is a substation in the French rail system between Paris and Rennes in Western France, fed from the RTE national power grid. An SVC Light®, supplied by Hitachi Energy, is operated by SNCF (the French railway company) for dynamic balancing of asymmetry between phases caused by the mode of traction feeding,
take-off of power between two phases in the three-phase grid. The project was executed in collaboration between Hitachi Energy, RFF (the owner of the railway infrastructure) and SNCF.
An analysis of the situation revealed that there was a need for a technical solution which could balance in an efficient and cost-effective way the heavy and strongly time-varying singlephase loads, as well as provide active filtering of harmonics from the trains. SVC Light fulfils these demands. A system such as SVC Light, having the ability to generate voltages with any amplitude and phase angle, can meet the conditions necessary for a load balancing system. The voltage can be controlled in amplitude, phase and frequency, with full independence between the three entities. In addition, with high-frequency pulse width modulation (PWM), SVC Light is also capable of synthesizing negative sequence voltages, a requirement for load balancing.
The SVC Light also performs the task of active filtering of harmonics generated by thyristor and diode locomotives up to and including the 9th harmonic without the need for passivefilters. Active filtering is made possible by the high dynamic response inherent in SVC Light.
By installing the SVC Light, the conditions set out in the National Grid Code concerning power quality at the point of connection to the grid of the traction feeder were fulfilled, i.e. requirements on limits for voltage fluctuations, phase unbalance and harmonic distortion were met. An alternative to the SVC Light would have been to build a new overhead line, to increase the fault level of the feeding grid. In feasibility studies
performed before the project, it was demonstrated that the SVC Light approach was considerably less costly as well as less time-consuming than building new lines1). Not having to build new lines was also very attractive from the environmental and concessional points of view.
|System voltage:||90 kV|
||16 Mvar inductive to 16 Mvar capacitive|
|VSC||16 MVA three-level, neutral-point clamped converter, IGBT based, pulse width modulated (PWM)|
||Dynamic negative sequence control of the fundamental current, dynamic positive and negative sequence control of harmonic currents, by means of a closed-loop, high-speed digital controller|
|Active filtering||Up to and including the 9th harmonic|