This paper investigates the possibilities for frequency support by synthetic inertia from variable speed wind turbines. A model for representing synthetic inertia in PSS/E (Power System Simulator for Engineering) has been developed. It allows the user to relatively simple implement different control strategies to find the most suitable strategy for a particular power system. Furthermore, it can be used regardless of the existence of wind turbine models in the power system model and is connected separately to any arbitrary bus in the power system. The results from the simulations show that the frequency nadir is reduced when implementing frequency support by synthetic inertia from wind turbines. As the wind power integration increases the frequency nadir is further improved when wind turbines can provide synthetic inertia. Regarding recovery, the results indicates that in order to minimise the risk of an under-frequency event the energy should be taken during a frequency overshoot and/or distributed in time, i.e. not all wind power plants should recover at the same time. However, these studies of synthetic inertia provided by wind turbines are still in the early stage and further work will be performed.

This work describes the design, implementation and evaluation of a novel fault location system for compensated networks. The work is performed as a part of the ongoing EU FP7 project called DICERN, involving five distribution network operators and several manufacturers and research institutes in Europe. In order to achieve its main goal of finding optimal level of intelligence in distribution grids the demonstration sites play a key role in achieving the central goals of the project. The aim of the Swedish demonstration is to gain knowledge on smart grid network operations and find a cost effective solution for monitoring the medium voltage (MV) network using “simple” sensors. The main objective is to geographically pinpoint faults in the distribution network and furthermore to evaluate the functionality of MV monitoring for fast and reliable fault identification and indicating distance to faults.

The automatic frequency containment reserve (FCR-N) is in place to keep the electric frequency within the interval 50.0 +/- 0.1 Hz during normal operation. This function is mainly provided by a number of hydropower plants where the turbine governor is set to control the discharge in proportion to the measured frequency deviation. In later years it has been shown that the disturbance damping is very low in an interval around 1/60 Hz and it is believed that proper tuning of the turbine governors that provide FCR-N can help mitigating this problem. New regulator settings have been suggested to improve the performance of the FCR-N, yet keeping the system robust and the wear on participating units at a minimum. It is now desired to investigate the possible effects of new governor settings on the overall power system frequency response. In a word, the overall performance for new governor settings are tested in a large scale power system model in this thesis paper. The frequency response with the newly suggested governor settings have been investigated when introducing a disturbance into the system. Secondly, the effects of the new governor settings on electro-mechanical oscillations are also investigated.

This paper describes a novel algorithm for feeder earthfault protection in compensated MV-networks. The algorithm combines optimal transient and steady-state performance into one function. The operation of the algorithm is based on multi-frequency neutral admittance measurement using the cumulative phasor summing technique. The main advantage of the proposed concept is that it provides valid measurement results regardless of the fault resistance value and the fault type, whether the fault has permanent, transient or an intermittent character. It also simplifies the applied protection scheme as coordination between separate protection functions dedicated to different fault types is no longer needed. First the paper introduces the theory of multi-frequency neutral admittance measurement. Secondly, the cumulative phasor summing technique is applied in this protection principle. Finally, the performance of the suggested protection algorithm is evaluated and compared with traditional earth-fault protection functions using data from simulations and comprehensive field tests conducted in a large 10 kV cable network with central and distributed compensation. The results show that the overall security and dependability of the protection can be significantly improved compared with the traditional earth-fault protection functions.