Single-phase 25 kV AC traction power supply systems (TPSSs) are widely used in high-speed railways, leading to an increasingly prominent problem of voltage unbalance (VU) in the power grid. To fairly regulate the system VU level, implementing VU limit pre-assessment is an urgent need. A grid connection scheme including traction transformer selection and exchange phase connection design is a vital part of TPSS design that obviously affects the VU factor of power systems. A uniform mathematical model is established using Thevenin's theorem, which reveals the impact of multiple grid connection schemes on the VU propagation behaviour of a three-phase grid. Afterwards, under the requirements of IEC/TR 61000-3-13, an improved VU limit pre-assessment process is proposed, which correlates mapping between the grid connection scheme and VU limit. The unbalance compensation calculation is given, adopting the allocation limit; furthermore, the optimal design of the grid connection scheme with minimised compensation capacity as an object is presented. The correctness of the model and the rationality of the pre-assessment process are verified by a case study.
ASJC Scopus subject areas
- Control and Systems Engineering
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering