# Preliminary Design of the Electrical Power Systems for DTT Nuclear Fusion Plant
## 3 Distribution System of DTT Facility
### Preliminary Layout and Configuration of the Electrical Distribution Network  
The power profile, the classification of the facility loads and the selection of the voltage levels allowed to draw up a preliminary layout of the DTT site and to identify the locations of five electrical load centers (LCs), denoted as LC1, LC2, LC3, LC4 and LC5, respectively, where the distribution equipment will be installed. The allocation of each LC, shown in Figure 3, has been chosen to be as barycentric with possible respect to the supplied loads in order to contain the cross section of power cables within acceptable limits. In this way, the maximum distance of each low-voltage load result is to be within 200-300 m from its LC.  
Each LC can supply all the different categories of loads (SSED, PPED, OL, EDG, UPS) and voltage level. However, a specific category or voltage level could be unnecessary in some cases.  
The MV distribution network of SSED (20 kV and 6 kV) will be arranged in double radial configuration, while the LV distribution network of SSED is arranged in single radial configuration. The MV distribution network of PPED (20 kV) is arranged in single radial configuration. Considering that the SSED LV distribution network is integrated by the  
Figure 2: Scheme of the DTT HV/MV substation (SS0).  
EDG and UPS systems, the redundancy of the electrical system is ensured leading to a good level of reliability.  
The five distribution LCs are supplied by the 20-kV system of the HV/MV substation, directly or indirectly.  
The electrical configuration of each LC is defined according to the following rules:  
1. For the 20-kV SSED section, the main power supply will be derived from the HV/MV substation and brought through two redundant 20-kV cable lines to each LC, where foreseen (like for LC1, LC2 and LC5, while LC3 and LC4 are powered at 400 V by LC5). Each couple of feeders will be connected to a SF\({}_{6}\)-gas insulated type (GIS) switchgear in double radial configuration. From each 20-kV SSED switchgear it will also be possible to directly feed loads classified as steady state.
2. In LCs where pulsed loads are also foreseen, power supply will be derived from the 20-kV PPED section of the HV/MV substation and brought to each concerned LC through non-redundant 20-kV feeders, each one made by a cable line. Each feeder will be connected to the switchgear in single radial configuration. The PPED distribution system will be at 20 kV only; pulsed loads which cannot be directly supplied at 20 kV shall be fed by the SSED distribution system.
3. Downstream from the 20-kV SSED switchgears, the distribution system may be composed of:  
Figure 3: Layout of DTT facility, with a focus on the 5 LCs. All the services are used for the operation of the tokamak located inside the DTT Hall.  
Double radial 6-kV distribution level obtained through redundant 20/6.3 kV power transformers connected to air-insulted type switchgears in double radial configuration.  
Single radial 400-230 V distribution level obtained through 20/0.42-0.24 kV power transformers connected to air-insulted type switchgears in single radial configuration with an additional isomer from the spare 20/0.42-0.24 kV power transformer installed in each LC.  
One or more EDG for each LC will be installed and connected to a dedicated LV distribution switchgear, depending on how the electrical network of the LC is configured. It distributes the emergency power to the switchgears where essential loads are connected or, in the case that all essential loads are connected to only one switchgear, the EDG will be directly connected to this latter.  
LV auxiliary service panels are foreseen to feed the minor static loads (such as lighting, power sockets, auxiliary loads, etc.) not directly related to the main processes and utilities. Each panel will be in single radial configuration, fed by a dedicated 0.4/0.42-0.24 kV isolation transformer with a spare isomer to connect an external service diesel generator, if necessary.