Some considerations concerning the distribution of electrical energy in a low voltage system

One presents the main disturbances sources from the distribution substations used for urban electric transportation systems: transformers from substations; three-phase supplying line; converters from substations; contact line and path rails. Using a quality analyzer, numerical recordings are obtained representing the waveforms of voltages and currents in a substation for the transformation medium to low voltage. The recorded data are transferred to a PC and processed, based on an original decomposition algorithm that implements the Fast Fourier Transform (FFT). The study case refers to a global consumption of a substation with an approximate active power of 590 kW and reactive power 65 kVAr. Harmonic decompositions of the recorded voltages and currents are made. One computes a series of quantities characteristic to the analyzed distorting regime (RMS values, total harmonic distortion for the phase voltages and phase currents, a.o.). The waveforms are afterward recomposed revealing that the computation error introduced by the decomposition algorithm is very small. The phases (re)active powers and total powers are determined. Interpretations of the determined values are provided. The analysis reveals the necessity to create a dedicated data acquisition system for each transformation substation in order to provide a complete monitoring system. Also should be useful the development of some real time recording and processing systems to realize a compensation efficient both from the distorting regime point of view and respectively from the compensation along the fundamental harmonic.