The no-load losses represent one of the most important problems for flywheels energy storage systems (FESS) which produce electrical energy from the kinetic energy stored with long waiting times between charging and discharging. This study presents a novel modular stator for use in synchronous permanent magnet (PM) electrical machine coupled to a FESS. The modular stator includes several sections of retractable yoke stator, displaceable in the radial direction. Each stator segment is composed of several coils, teeth and its corresponding back iron section. A removable back iron yoke stator allows reducing the iron losses in the ferromagnetic core of the PM motor/generator during stand-by operation mode in FESS. In stand-by mode, with the stator in a retracted position, the iron losses are reduced up to 95% when the air gap length is increased 20 mm.

Renewable power is expected to increase drastically in the coming years due to the energy transition. A large part of the newly installed generators will be connected to the power system through inverters and electronic converters, whose behaviour differs from the generators connected synchronously to the network. One of the main differences is the current contribution during symmetrical and asymmetrical faults which can affect protection systems. New grid codes establish requirements for fast current injection, but the converter’s maximum current limitations during faults make it difficult to establish control strategies for such current contribution. This paper studies the performance of faulted phase selector algorithm of a commercial relay under the current contribution from renewables before unbalanced faults. Two positive and negative sequence current injection strategies in compliance with new Spanish grid code requirements are proposed and tested under fault conditions in HiL (Hardware in the Loop). Test results show that the selected injection strategy affects the fault phase identification algorithm. Furthermore, the negative sequence injection requirements established in the new grid code improve the relay performance when line-to-line faults are applied, but they are not enough to identify all fault types.

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The high penetration of renewable energies will affect the performance of present protection algorithms due to fault current injection from generators based on power electronics. This paper explains the process followed for analyzing this effect on distance protection and the development of a new algorithm that improves its performance in such a scenario. First of all, four commercial protection relays were tested before fault current contribution from photovoltaic system and full converter wind turbines using the hardware in the loop technique. The analysis of results obtained, jointly with a theoretical analysis based on commonly used protection strategy of superimposed quantities, lead to a conclusion about the cause of observed wrong behaviors of present protection algorithms under a high penetration of renewables. According to these conclusions, a new algorithm has been developed to improve the detection of faulted phase selection and directionality on distance protection under a short circuit current fed by renewable energy sources.

In this paper, the capabilities of a Wide-Area Protection and Control (WAMPAC) lab-scale demonstration (DEMO) is presented. This lab will be used in Work Package 6 of H2020 FARCROSS Project for testing wide-area applications previously to their commissioning in a real DEMO in the Greek Transmission System. The capabilities of this lab-scaled DEMO are presented using the implementation of two different monitoring and protection applications for a proof of concepts. The first application is related to detection of inter-area power oscillations using PMU measurements and applying a remedial action. The second application deals with the comparison of the behavior of three line differential protection strategies: classical implementation using two fiber optic communicated relays, a solution based on values received from PMU and an algorithm receiving IEC 61850 Sampled Values and using open-source libraries in a common computer. These applications are tested by closing the loop using real protection and control hardware in the laboratory with an RTDS ™ simulator.