Voltage Sag Propagation Caused by Faults in Medium Voltage Distribution Network

Underground cables are being increasingly constructed in modern power distribution networks, however overhead lines are still present, making the system more exposed to faults. Faults from medium voltage networks propagate throughout the network and then experienced by low-voltage customers as voltage sags. Voltage sags have become increasingly important when considering the various power quality issues that cause inconvenience to customers. For some customers voltage sags cause, especially high costs. In this paper, different fault types at the medium voltage level and the sag propagated throughout the network are analyzed. Asymmetrical faults can cause problems for protection devices since they propagate differently throughout the distribution network, and distort the phase to ground voltages on the different voltage levels. Experimental results obtained from the Bosnia and Herzegovina distribution system show the significance of appropriate voltage sag propagation understanding. The power distribution companies should understand the voltage sags experienced in their networks and develop strategies for decreasing the influence of voltage sags. Thus, voltage sags analysis should be an important part of power distribution planning and an important element in a comprehensive power system analysis.