Experimental characterisation of active and non‐active harmonic power flow of AC rolling stock and interaction with the supply network

Abstract

In AC electrified railways, there is a significant exchange of power at fundamental and harmonics in quite dynamic conditions. Harmonic patterns of AC rolling stock and railway networks are analysed in terms of active and non‐active power flow, relating it to the characteristic of the network and to operating conditions, synthesised in the fundamental current intensity and speed. Herein, it is shown that correlation and clustering can separate distortion terms of internal and external origin also without a priori information. The use of harmonic power terms (product of voltage and current components) shows improved robustness with respect to the analysis of the voltage and current components alone.

Detection of Harmonic Overvoltage and Resonance in AC Railways using Measured Pantograph Electrical Quantities

“…Then it is not meant that the active power term Ph is maximum overall, but its fraction taken with respect to the total harmonic apparent power Ah = (Ph 2 +Qh 2 ) (namely the harmonic displacement factor dh = Ph/Ah) is. This is clear as all low-order harmonics are characterized by large values of apparent power and consequently, in proportion, active power as well, as demonstrated in [39]. The use of dh allows a normalized weighting of the active power flow at all frequencies without problems of scale, with which resonance conditions may be characterized and identified.…”

“…However, cancellation of reactive power at a given harmonic is a necessary, but not sufficient, condition for identification of network resonances, series or parallel. In fact, there are transient situations, as identified in the polar plots of the harmonic active and reactive power components in [39], for which the reactive power term may be temporarily very small with active power prevailing. This behavior was investigated in [40] to identify suitable PQ source indicators, focusing in particular onto the sign and intensity of the active power indicator.…”

“…This approach is in line with [18], but it is ineffective in practice, if the real behavior of the AC railway and rolling stock is considered: • Low-order harmonics are ubiquitous in AC railways [1,4,39], and may or may not be produced by the rolling stock used for tests, depending on the type of the on-board converters; modern 4QCs (four-quadrant converters) are not in general a source of low-order harmonics. Low-order harmonics have the largest amplitude of all voltage spectrum components and they would mask the effect in the overall THD of higher-order components at resonance .…”

Detection of Harmonic Overvoltage and Resonance in AC Railways Using Measured Pantograph Electrical Quantities

“…It is not meant by this that the active power term P h is maximum overall, but its fraction taken with respect to the total harmonic apparent power A h = √ (P h 2 +Q h 2 ) (namely the harmonic displacement factor d h = P h /A h ) is. This is clear as all low-order harmonics are characterized by large values of apparent power and consequently, in proportion, active power as well, as demonstrated in [42]. The use of d h allows a normalized weighting of the active power flow at all frequencies without problems of scale, with which resonance conditions may be characterized and identified.…”

Power quality metrics for DC grids with pulsed power loads

“…The use and processing of power trajectory is particularly suited for PPLs and opens new possibilities of revisiting "traditional" PQ metrics with interesting performances and results. The better informative content of power with respect to voltage and current taken separately was pointed out in [46], when investigating internal and external sources of harmonic emissions in AC railways.…”