Power quality improvement case study of the connection of four 1.6 MVA flywheel dynamic UPS systems to a medium voltage distribution network

This paper investigates the feasibility of connecting flywheel dynamic UPS (uninterruptible power supply) systems to a 20 kV distribution network. The studied UPS systems implied diesel generators for long duration power cuts on the RV side. Different aspects are considered: quality of supply including harmonics, voltage and frequency control, impact on the protection system, the neutral grounding and the customers´ protection devices, dynamic behavior and stability of the whole system (UPS and network) etc. Results of a case study carried out on an existing medium voltage network are presented, both for normal and islanded operation of the network