Probability of Voltage Sags Depending on the Characteristics of Medium Voltage Networks

This paper presents how the characteristics of medium voltage (MV) networks affect the probability of the voltage sags experienced by a low voltage customer. Faults occurring in the MV level are typically an important origin of voltage sags. Thus, when aiming to lower the sag probability the characteristics of the local MV network have an important role. This paper concentrates to various conventional solutions of network components and connections. An own primary transformer and an MV network with underground cables of minimum feeder lengths is a superior solution for a sag-sensitive customer. In a case of overhead line MV networks, surge arresters should be used for overvoltage protection of pole-mounted power distribution transformers. Surprisingly, not necessarily all stages of the overall development of power distribution networks result to a lower probability of voltage sags. Mixed- overhead/underground cable-MV networks and some stages of distribution automation included characteristics that need a careful sag analysis