Assessment of voltage dips in HV-networks: deduction of complex voltages from the measured RMS voltages

Many network operators are doing important efforts to collect relevant and precise information about voltage dips in HV networks. This information is however not relevant for the end user, who is connected at a lower voltage level, often behind a Dy transformer and who will not experience the same voltage dips as recorded by the power quality monitors. In most cases the power quality monitors only records rms voltages during dips and the deduction of the characteristics at lower voltage levels is not possible. The voltage phasors are required to derive this kind of information. In this paper a new method is proposed which enables to obtain valuable statistical information for the network users from existing monitors and databases, which only contain information about rms voltages. Algorithms are proposed to estimate the dip type from the relation between the three rms voltages during the dip. Knowing the dip type the phasors can be calculated. Good results are obtained for faults in transmission networks, especially on overhead lines. The more severe the voltage dip, the better the performance of the algorithm.