Abstract :
Given that the conclusion of field tests was that islanding events have to do somehow with the transient behaviour of the inverters and their interaction with the loads connected to the network, two different analyses have been carried out, considering both passive methods and Sandia Frequency Shift Islanding Detection Method (SFS). The aim of these analyses is to understand the reasons for the failures of protection systems embedded in inverters, in order to be able to develop improved detection methods. The analyses follow two different approaches. The first one is focused on the inverter behaviour, taking into account several aspects, such as association with different kind and number of inverters, constants used in SFS, quality factor or islanding detection with presence of motors among the loads. The second approach takes into account their integration into a large network, studying SFS performance in presence of active and reactive power balance between generation and active loads in the network and including the simulation of the interaction among inverters with different anti-islanding configurations, different sites and power control parameterization. The results show that setting of inverter parameters (power control loops, SFS parameters and PLL system) in addition to load characteristics out of the DSO control (resistive or constant power loads, presence of asynchronous motors) could make the islanding detection system inoperative.
