# Preliminary Design of the Electrical Power Systems for DTT Nuclear Fusion Plant
## 1 Introduction  
The Divertor Tokamak Test (DTT) facility is one of the main projects within the framework of the European Roadmap to the realization of fusion energy [1] whose final goal is the development of DEMO [2, 3], the first demonstrative power plant able to deliver to an external grid a net electrical energy produced by nuclear-fusion processes. DEMO is presently under design and is expected to be connected to the European grid by 2050 [1].  
Among the eight missions towards fusion electricity defined in the European Roadmap, DTT is a key facility in the framework of Mission 2 (\"Heat-exhaust system\"), aiming to identify the optimal solution for the problem of disposing the heat load through the \"divertor\" [4, 5], which is one of the main components of the future commercial reactors. Even though some conventional approaches for the divertor systems will be tested in the international experiment ITER, under construction in France [6], it could be difficult to extrapolate them to the operating conditions expected in DEMO or in a commercial power plant. For this reason, the DTT facility is a high-performance superconducting tokamak [4] addressed to explore alternative solutions for the power exhaust problem by testing different divertor geometries and materials suitable for DEMO [7].  
The construction of the DTT facility started in the ENEA Research Center in Frascati, Italy, with several scientific collaborations and financial supports including the European Agency EUROfusion. The number of DTT partners (universities, research bodies and companies) is continuously growing [8].  
The design of the electrical power systems of a nuclear-fusion plant is a crucial issue, especially to investigate the possibility to adopt it as an energy source. Unlike DEMO, which is designed to deliver the net electrical energy to the grid [3,9], DTT is an experimental plant, which means that its electrical power systems will be \"simpler\" than those expected for DEMO [10] and the nuclear requirements are less stringent [11]. Nevertheless, the power systems are not trivial in terms of size and complexity, especially in terms of power density [12, 13, 14]. In fact, all the main types of loads present in ITER (and maybe in DEMO) will be implemented in DTT [12, 15, 16]: Converter for superconducting and copper coils [14], electron cyclotron resonance heating (ECRH) [17], ion cyclotron resonance heating (ICRH) [18], negative neutral beam injector (NBI) [19], cryogenic and water cooling systems and so on [10, 16]. Therefore, DTT may also be a good reduced-scale experiment for the study and the optimization of the power systems for possible ITER upgrades and for DEMO.  
As a part of the process to define the electrical supply system of DTT, the identification of the electrical loads is the first necessary step [16]. Since the loads have been characterized from a quantitative and a qualitative point of view, it is possible to proceed to the preliminary design and sizing of the internal distribution network.  
The present paper describes the preliminary studies to verify the design of the electrical distribution and protection systems of the DTT plant. The scheme obtained for the electrical system was implemented in the DIgSILENT PowerFactory software environment [20] in order to analyze the trends of power flows and to verify the design of the main electrical components.  
The paper is divided in five sections. Section 2 presents the main DTT features and shows how the electrical loads were characterized and classified. Section 3 describes the organization of the distribution system and provides a first estimation of the required power. Section 4 presents the results of the model implemented for the preliminary design of the power systems (power flow and fault analyses). Section 5 reports the conclusions.