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Power quality (and monitoring) in railway systems

26 September 2013  •  Author(s): Marco Filipe Santos, Head of the Catenary and Electric Traction Department, REFER Engineering S.A

Electrical compatibility between fixed installations and rolling stock, at power supply level, is paramount when dealing with power quality, system availability and reliability. This article addresses power quality and power quality monitoring on alternate current 25 kV electrification systems, focused on overvoltages generated by near resonance frequency harmonics.

Theoretical background

According to Ohm’s Law, when a voltage is applied to an electrical circuit the resulting current flow is inversely proportional to the circuit impedance. By the same law, if an electric current is injected in a circuit the resulting voltage is directly proportional to the circuit impedance.

By definition the electrical impedance is the measure of opposition that an electric circuit presents to the flow of current. In alternating current (AC) the impedance has two components: resistance and reactance. The resistance component is intrinsic to the materials and shape of electrical elements. The reactance relates to the electromagnetic induction phenomena between electrical elements. While resistance is invariable with frequency, reactance is frequency dependent.

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