Electromagnetic compatibility and power quality problems at low frequency for loads from an urban transportation system and in a power substation

This paper deals with energy/power quality issues, correlated with Electromagnetic Compatibility (EMC) and electromagnetic interferences (EMI) which appear at urban transportation systems. One presents, briefly, some aspects regarding powers definitions for harmonic and/or unsymmetrical regimes from three-phase circuits, applicable to loads supplied from the a.c. line through low voltage power transformers and uncontrolled three-phase rectifiers. It is analysed the case of a driving system with d.c. motor and chopper, supplied from the d.c. line, which induces a significant non-sinusoidal regime in the a.c. network. The cases in which the load is not compensated, respectively compensated through an active filter are also analyzed through tests on stand. Aspects regarding powers and power flows for both cases are also discussed. Furthermore, the obtained data are compared using the quality standards IEEE 519/1992 and 1459/2000. One discusses the obeying of quality standards and some aspects, which are not approached in the specialty literature, concerning the corresponding EMC and EMI issues. Problems related to the tested driving system connection to the supplying system from the power substation for an urban transportation system are briefly presented. The waveforms of currents through the active filter are depicted. Some conclusions on approaching EMC and EMI at low frequencies, with an extension over 2 kHz and the relation with the IEC 61000-4-30 standard are also presented. It is underlined the necessity of treating energy/power quality issues in correlation with issues regarding EMC and EMI at low frequency for this type of loads.