Abstract
Voltage unbalance in power systems feeding AC traction power systems is a worldwide known problem. One of the main aspects of this problem is the negative effect of voltage unbalance on motor loads causing operating problems and economic damage. It is necessary to perform unbalanced power flow studies and calculate voltage unbalance indexes to assess this negative effect of voltage unbalance and the develop of compensating measures during the design stage. Usually, calculations of the AC traction power supply system and the distribution network feeding it are carried out separately during the design of new lines of railways electrified by alternating current (AC) and reconstructing of existing ones. This approach is a source of deviations in the power flow studies because the lack of consideration of mutual influences between the traction power system and the distribution power system. In this paper, we compare a digital model in which the traction power supply system and the distribution network are modeled separately with a model that considers mutual influences between the traction and external power supply systems, including power flows through the traction network caused by the distribution network (transit currents). For digital modeling of these processes, authors used ETAPTM software with eTraXTM package. It allows to run unbalanced power flow studies when the generation and load are being changed over time, including train movement. During a separate simulation of the traction power system and distribution network, traction network was modelled using the equivalent sources connected to traction substation buses and the distribution network was modeled taking into account the fact that traction load was given from the simulation of the traction power system. The traction load was considered as lumped loads connected to the traction substation buses.At the same time, in both cases, the unbalanced power flow study was carried out by the phase domain method. Based on the results of two models comparison, it was concluded that the combined model containing a traction power supply system and distribution network, is more effective in terms of improving the accuracy of assessment voltage unbalance in accordance with current regulatory and technical documents on power quality.
Highlights
Voltage unbalance is the well-known worldwide important in power grids feeding alternating current (AC) traction power systems
In this paper authors compares the traditional way of AC traction power system modeling with equivalent sources with the way using the detailed model of the upstream power system
The main purpose of this paper is to show the benefits of the co-simulation of AC traction power and the upstream power system and the difference between these two approaches of AC traction power system modeling for design and operation
Summary
Voltage unbalance is the well-known worldwide important in power grids feeding AC traction power systems. AC traction power system trains are 1-phase loads with huge power consumption causing unbalanced power flows through traction substations. It causes voltage unbalance at all buses of the power system. In this paper authors compares the traditional way of AC traction power system modeling with equivalent sources with the way using the detailed model of the upstream power system. The traditional models with equivalent sources at each AC traction substation cannot provide these results. The main purpose of this paper is to show the benefits of the co-simulation of AC traction power and the upstream power system and the difference between these two approaches of AC traction power system modeling for design and operation
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