Simulations on harmonic current distributions and voltages in AC-DC voltage interface areas

In the last several years, Holland Railconsult has used the simulation tool SimspoG to simulate the current and voltage distribution in 25 kV traction power supply systems. It is used for energy-demand, short-circuit, step and touch voltage and thermal calculations. Occasionally it has also been used to simulate track circuits, including the effects of asymmetric faults like a broken rail. In the last two years, significant enhancements have been made to extend the maximum number of conductors, to increase the maximum length of the models and to decrease the simulation time.
The model is primarily developed for simulations on 25 kV 50 Hz systems, therefore some simplifications were made in the past. For example, capacitive currents have been neglected, due to the fact that (at 50 Hz) these are very small compared to normal traction currents. For studies on higher frequencies, these currents can no longer be neglected and all capacitances must be included in the model.
Another aspect is the simulation of system separation zones between the existing Dutch 1500 V DC infrastructure and the new 25 kV 50 Hz lines. In order to perform detailed calculations on these interfaces, some specific components are required, like resonant filters and booster transformers, which were not included in the model until now.
Simulations on separation zones are necessary to assess the influence on victim systems like track circuits or the effects of stray current corrosion of the AC earthing system. Due to the frequency dependent characteristics of resonant filters and booster transformers, it is important to include harmonics in the calculations.
Holland Railconsult has extended the existing SimspoG model with those components and added capacitive coupling between all conductors.
This paper describes the steps we followed to add these extensions to the model. For a start, some background information about SimspoG itself is presented.