Harmonics Analysis Due to Connecting an Electrical Traction to A 3-phase Power Supply System Through V/V Transformer

Ammar mohamad Elagab

Abstract


The wide application and usage of electrical traction system presents utilities with planning and
operation challenges. Electric railways impose several power quality problems to the utility grid. Such as generated
large negative sequence components (NSCs), undesirable harmonics, cause system voltage and current unbalance.
Harmonics and unbalanced voltage also may cause negative effects on the components of the power system such as:
overheating the transformers and the transmission lines, vibration and cause torque reduction of rotating machines,
additional losses of lines and transformers, interference with communication systems, malfunctions of protection
relays, measuring instrument error. All these problems have become more and more significant. This paper is an
attempt to quantify and assess the impact of electrical traction on the grid side through a V/V transformer. Firstly in
this paper, the typical utility power grid and traction power supply system model are designed. Then, the traction
system is integrated with the power supply system through a V/V transformer. Two cases of the connection are
considered. The first case, when the traction system is connected to one side of transformer. The second case, when
there is a balance traction load on the both transformer side. Finally, PSCAD simulation is used to analyze the power
system quality and to estimate the harmonics that are generated in the traction and power supply system sides due to
this integration. The simulation results show that, in the both cases, high levels of voltage and current harmonics are
generated in the traction side. These harmonics are generated only on the phases that the traction is connected to
them, while the other phase will not be affected. Also, it is observed that, the generated harmonics at the traction
load side have also been transferred to the power supply system side though the transformer.

Keywords


Electric traction, Negative sequence components, Harmonics, Power quality, V/V transformer, PSCAD Simulation

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