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ENEA - Fusion division

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FAST — Power Supply System

Contact: Maurizio Santinelli
e-mail: maurizio.santinelli@enea.it
tel.    : 0039 06 9400 5781
fax.   : 0039 06 9400 5734

The FAST power supply system includes three main subsystems: the 400 kV switchyards, the poloidal field coil (PFC) power supplies and the toroidal field (TFC) power supplies; input data for its design have been:

  1. the MAturns required by the 6.5MA 7.5 T reference scenario;
  2. inductance matrix of the system;
  3. coils resistances.

First step of the work has been the realization of an iterative process that, even if preserving the plasma equilibrium, minimizes the cost of the plants, acting on the currents diagrams and the number of turns (Nturn) of the poloidal coils.
Table 1 shows the number of turns of the poloidal coils , it can be noticed that the CS2U and CS2L, CS1U and CS1L, PF3 and PF4 coils are connected in series, respectively.

Table 1: Turns number of the poloidal coils
CS3U CS3L CS2 CS1 PF1 PF6 PF2 PF5 PF3_4 Plasma
432 432 500 500 38 304 30 178 120 1

Having set the coils currents and the power supplies voltages (see fig.1), the commutation resistors (switching network) have been calculated; whilst the related inductances matrix is displayed in table 2.

Coils Voltagesfig. 1: Coils Voltages (V)
Mutual and self inductances in mHTable: 2 Mutual and self inductances in mH

Each circuit, for the supply of the TFC and the PFC, is generally made by converter transformer, a thyristor converter unit, a protective crow-bar and a high-speed, solid state switches for the additional resistance units.
Figure 2 shows the total power for the 6.5 MA scenario, where are also included: a local reactive power compensation ( by means of Static VAR Compensator, SVC) of 80 MVAr a total heating power of 100 MW (at grid level) and a stationary load of 25 MW.

Active (MW), reactive (MVAr) and total power (MVA)fig. 2 Active (MW), reactive (MVAr) and total power (MVA)

Due to the amount of requested power, connecting to a powerful node of the 400 kV grid is needed. For this reason, an accurate check by the TERNA (owner of the National Transmission Grid, RTN), including both active and reactive power effects on the specific grid, has been performed providing positive results for two possible ENEA’s sites (see following section).
Within the assumed 400 kV reference solution, FAST needs a dedicated switchyard to supply: PFC, TFC, Additional Heating Systems and Auxiliaries. All loads are fed by one main step down transformer (400/36 kV) with three secondary windings: two (225 MVA each) star connected and grounded through a resistor, to supply FAST and one (150 MVA) delta connected to allow free circulation of third harmonic currents.

Site assessment

An assessment of the generic site requirements has been made. The following elements have been considered: building availability and erection capability, water cooling and electrical power availability.
The requests in terms of power from the grid, cooling water and building volume are given in Table 3.

Power, cooling and volume requestsTable 3: Power, cooling and volume requests