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.